-,-v 

Profosswnal Paper No. 3 . f B, Doscriplive Geology, 22 

enos\ D. Petrography and Mineralogy, 21 

DEPA HT:'II K.\'T OF ill ~ J);TEHJUR I 

U:t\ ITED TATE~ GEOLOG L ' \L .' H. EY 

(; H AKLJo:l-' ll. \L\1.,('0'1''1', llJHf: :TOH 

1 

~/llll~il ~~ W~II I! 3 1818 00019015 5 

ri Jr 

GEOLOGY \Nl) PETROGR \PHY 

• OF 

H\' 

JOSEPH SILAS DILLER and HORAOE BUSHNELL PATTON 

51109 

'' ,' III T TO T 

G V •~ Jt N M 1•: N T l> Jt I " T l :-< G 0 I•' :F 1 0 'E 

1HU 2 

CON TENTS. 

Pngc. 

lxTHuut:C'I'I O:<, by J o:eph Silas Dillel' ___ ________ ___ ____ ________ ___ - ----- __ ---- ------ ____ ____ 5 

PAn'r J. The "eolo 'Y of Crater .Lake ational Park, by Jo eph Sil a.'S Diller (Pis. I-XIII) _ _ _ _ _ _ ll 

l'.IHT 11. The petrography of 1·a.ter Lake National Park, by Horace Bu bnell Patton (PI.. 

XIV-XIX) ______________ . ___ _____ ___ ______ ________ __ ____ ___ __ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 6:3 

l NDEX. _ •• ___ •••••• •• ••••••••••••••••••••••• •••••••• ••••••••••• • •••••••••••••••••••• • ••••• 165 

3 

' 

IN T RODr CT I ON. 

B · .1 I'n tln.A. DtLLEH. 

TwC'nty ·y<'ar: no·o ra ter Lake wa:-; u nkn o wn to tb grncrnl puhlie, bnt 1-i in e , 

then a knowledge 0f it:-; r ' markah! <' f<'nturel-i ha: bee n sr r n.d <throa I t hroug h tho 

pre ·, ftnd Congr ss r ecou·nized its wort h as :ut ed ucationa l fNtturr and mnd C' it ;t 

na tional park hy th act •ti proved ::\'lay 22, 1902. 

As d tined in the hill, the park i: " b undC'd north by tlw pamllrl forty -th ree 

degr <'><fo ur minutr:-; north "latitude, s utb by f rty -two cl g n•es forty · •ight utinutc:; 

north lati t uc!C'. nl-i t hy the mcridinn ne hundrrd and t\I"C' nt ·-two degr c s Wf'l't lOJwit ud ., and WCI-it hy the meridian on hundred a nd twC'nty-two deoTee:; 8ixteen ntinutes 

wrst long itud , h:1Ying ftll nr a of t wo hundr rl nncl fort.v-ni nr 1-iQWU' mil . . ' 

Th C' ~b nd ,.:h C't of ni tcd tnte ' Grologi ·a l 'ur v<'y . o n the scalE' of+ mile to 

1 in h, indudc thC' arra lying brtwe n meridians 1:22° and 123° and pamlle l: ±2° and 

43° . This map inC'ind s tb r g ion b tw e n A.·hlancl a nd 'rater Lak . On n.c ount of 

t he g r eat ci ntific int re,.:L of 'ratN Lak ft l-ip ccial nutp, 1 nown as th e Crate r Lake 

spe ial he t. was pr parrd on the sc·;l le of l mi le to :w inch in ludi:1g the countr5· 

immediately n.dja cnt to 'rat r Lake. b tw C' n me ridia n 122° and L2° 15' a nd prtralle b -:1:2°. 50' nnd 4:3' -t'. From tht>s two mar : tlw ac ·ompan.ving- map ol' thr ratC' r 

Ln.k National Par k (Pl. I) ha.-. l>r l n prt' p:trrd. 

Th r t wo pape rs puhlis brd hr rr rdrr pntcti a ll y to thr whol e r egion in ·luded 

in tlw National Parle The one. P!trt J, tr at..,; p rima ril.v of t hr ~·eo oo·y . the development ol' thE' gr<'at ,·ole:tno, Mount :Mnzamn and its olhtp,;r, whit"h o·ftvo birtb o 

Crater Lak ; the othC'r. Part 11, d ttl · with thr [ trC'g-raph.1·, a nd g iv s a sprci:tl 

de cription of tho v;u ou~ rock::; oecu rr in o- in tho park. 

Q,·/y/11 f((tnt' 11all1f' .Llfouuf JfCtZ((11Ul a.- \. OT at impetU to the•:pread Of infOl'-

tllati n corH.:e rning 'mtrr L•tke wa g i1·cn by th ::\Jazamas of Por tland, Or g. , wh 

b lcl a mecti rw nt th lake in Aug-u'-'t, l896 whieh attracted many 1·i:it r:. Th prinu An Hcconnt of the di ('()\ ry of Crut.cr Lnkc nncl r('l'cr •n('l' to it ~ litPI'u.turc wilt bo ffluud in Mazu nw., V ol. I , 0 o. '2. 

Cm tcr· I.o,k number, 1 ~)7 : ~utio ullll ogTftphit )laguziu •, \ ol. V II I, Jl. :33, ~t nd the Annual l<cpol'l nf til{' ith ~Oiti n 

11 ti tHio n 9i, p. 31iU. 

5 
6 GEOLOGY OF RATER LAKE NA'J'IO AL PARK. 

cipal f ature:; in the hi tory of the lake had previou. ly be n made out, and th 

Mazama ·, recognizing th fact that the oTent p ak whi h Wfli' nearly cl e:tJ·oyed in 

preparing the pit for the lak hftd no mw1 , o·avc it th name of th ir own societ_y. 

pon the rim of the llLke are <L nulllbe r of smfdl peak:-;, PfLc h having it~ own de 'igmttion . Th te rlll ;)lount Mazama r ef rs to the whol · rim ncir ·ling th • lake. It i:-; 

but a mer remnant of the one' lofty p ak th real Mount Mazama, whi h ro far 

into the r gion of temal now. To g t tt ba ·i. · for reconstructing th original 

Mount Mazama it i. nece sary to :tudy in d tail th Rtmcture and c mpo. iti n 

of it.c, foundation, now ·o attracti' ely eli. pla d in th n irc·ling I iff.· of 'rat r 

Lake. 

RO TES r.ro CRArl'ER J_, KE. 

Crater Lake is deeply tin th ummit of th a ade Rang about 65 mil e 

north of the California line. It can b r a h d only by privat on yanc ov r 

about 0 mile of mountain road from • bland or M ilford, on th outh ro Pacific 

Railroad, in th Roo-ue River Valley of outhern Or g n ( ·ee !:ig. 1 p. 1 ), or from 

Ager, on the sam railroad , in northern C~tlifornia by way of Klnmath Hot 'pring:-; 

nnd Klamath Fa,ll . 

Rogue River Vnlley mark b line b tween th e i kiyou Mountain of tlw 

Kl,tmath g roup on th we t and the Ca cade Rang on th e ra t. Th journey fr m 

th railroad to Crater Lake afford one a o·ood opportunity to ob · t·v ome of th e 

most importc<tnt featur of thi great pil of lava:. The Ca cade Rano·e in south rn 

Oregon i · a broad irregular platform, terminating rath r abruptly in pia e., p cially 

at the w :;tem hord r, where the underly ing Cretac ou and T rtiary · dimcnk 

om to th : urfa e. It i urmount d by volcanic con . and tream · of la\'a, whi h 

arc gen rally ·mooth, but ometim rough and rugg d. Th cone: ,·ary g r atl\• 

, in :ize and are di,'tributed without regularity, a f ,atur wbi.ch i · well illu trat d in 

Pl. ll. The photograph wa taken acro:s the w tern dge of 'rat r Lake. Th 

sharp peak on the right i Un ion P eak a,nd in the di ·tance i. Mount Pitt. Ea.ch 

coni caJ hil l ba" been an actiYe volcan . Th fragm nt.~ blown out ly violent 

eruption haY fall en a,bout th e orifi e from whi ch th y i. sued a,ncl built up cincl r 

·one.:. :From th ir base: have . pr ad treams of lava ( oulee ), rai irw the gc'n l'al 

level of th country between tbP. con . At ·ome vente;; man. · erupti ns, l>oth 

cxplo:i vr and effu ·iv , have built up large cone ·, lik Pitt, ba t:A. and Hood. 

Their internal :truc·ture i. revealed by th e wall of the canyon" carved in th ir 

~lope , and tlwy are found to be composed of overlapping la ers of lava and volca,ni 

conglomerate. Thi. type of ..: tructur i · w II illu:;trated 1n the l:M ·e of Mou nt 

Ma7.ama,. 

Tlw Dead !ndian ?'oute .from l ltland. Oreg.- The JOurney from A ·hlnnd 

hy the D nd Indian I'Oacl tl'os. cs the rang·c whPI' , th e average altitude i I . · 
ROt 'J'E~ 'l'O C'R A'I'"RH J,A KF.. 7 

thnn o.OOO fert. and afl'ords a f~li r vi w of th low part of til<' rnng·c tnw rsNI 

h_,. the Klamath Rive r. 

the range, and espce i<tll.r f the 

Mount Pitt (e lcnttion ll. HiO feet) 

rO<Ld at Litke of the \\'oo(l$. Th 

'n~tc r Lake region. 111:1~· hr obtainrd rrotll 

whid1 li es within a t wo da.n-;' trip front t;his 

rmtd skirts Prliean B<L,\" of 1 lamath L tkr. 

famous for its ti.·hing. and afte r running northward for <LbouL ~() milrs along tlw 

cast rn foot of the range it as ·end;:, th slop along· th<' ('!1.11,\' n of Anna 11'P<'k 

to th e rim of 'mte r Lah. 

Tlu> l\.lriiJirtflt Frt/1.~ 1'0idr' frrntl Ar;d·. U ti.- Tbe apJroach from th<' rast tna.'· 

hr ma.de also by a. long r 1·oute, leaving- tlw ra i !road at .\ g-p r. 'al., and tnl\· I i ng· 

b_,. stag<' road along th Klalllath Ri,·cr. through tlt(' 'ascad RRngr o Klamath 

.Falls and Fort Klamath , from whic·h point 'rate r Lak<' is only 20 ntiles distHnt 

hy way of th Anna CrrPk roa 1, :tlr ~td: · nott•d. Th r o ldrr tilt d lav:v of tlw 

Cascade Rang dippitw to thP cast arc wPil t•xpos •d on thi · route a.t tn!Lny 

points n.long the Klamath Hin•r 1·oad between Ao·er a.nd Kl a11tath !Tot ' pring.l' 

A cr . th rdg s f these lams. nea rly LOOO fe t aho,·c the lH'P:>Pnt rin r hPd , 

j,· a n anci nt wide Yalle:· of thE' K lamn.th River, a:>.·ocinted with o·cntk topogmpltic 

r li f at high er l ,-cl.·. Lnt r htva hax c·ross d the rang in hi;; wid oil milt' \' 

~Lnd the Klamath Ri,·er ha.· cut a deep ('anyon in t h m. 'Yithjn this young nLtlyon north of Bogus po:-t- Ake. her e ha · been a ,-ok anic; rupti on. forming a dattt 

across th ' K lamath and a ·onsequent ponding of the ri,·e r, in \\'hi c· h a mnss of 

whitE' diatom ~rt h 'ras formed. Th produet.· of this ruption an' mu<"h _voung~>r 

than an)· other.· kn own to tb writ r in the neio·hborino· portion of th ' ascndt• 

Range. 

Tit R ogu R hY!'!' ·rout . .f?'OIII jJiedford. 01·err - From Medford the roa.d IH· 

way f Roon(' Hivc r, although 7.~ mil :; in length, is som0what the ·hortcst r outr. 

It afford some fin e Yi w.· of th ca.nyons nnl rn.pid · of that turbul nt :;trea.nt 

and of the hio-h fal ls, whc r it r -cei,- s it:> a.ftlue nt ·. C:>p<'cially fill ' r ec k, b lo\\' 

Prosp ct. \. few mil , h low th mou h of l ' nion r E' k i · a r emarkahl nat.ural 

bridge of Ia ,-a, but :;ome distance from the main road. ~tri ki tw features <dong 

th e roads on both side. · f the mountain , within ~0 mil es of th la k i ll' th e 

plains devrlop d upon a g r ea.t ma ·s of Yol canie detritus filling the nd l Y"-· 

!\('rO ·::; thc:e plains Anna Cr<'E' k and Roo·uc Hir r ha,·e carv cl deep, narrow 

l'n nyons with finely sculptnr d wa ll -, which th e road: foil w for .·on1r di ·tanec. 

Th mfLin road, who.·c gra.de i:s in o·en em l YCJ',Y ge ntle, <· ros" · he :> untmit 3 

mil s .·outh of Crater Lakr, and from the \"\1 .· tern ·lope t1'Hr this I oint th ' en' ·t 

o f Lhc ri m is reat·hed by a r oad with :>e,·eral h avy grade ·. Tben' arc good 

c-n.mping· groun d: with II nty of pa tnrE' n 'astlc Cr el< b yond the fork s of thr 

' r nThJs cel cbmted heo\lth re,ort hu< 11 KOnd hotel, fine ceucry, hunting, und fishing. 
GJWLOGY OL< RA'TF.Tt AK ~ ATTONAL P.Al K . 

road a nd within 2t mil e. of t h lakr. At thr end of th road , 0 11 th nm of 

'rater Lake, the carn ping phte :-; ar c tine, hut pasturr and wate r ar not :-;o 

ab unda nt nor so a ·ily obta in ed. Thor a r a · yet no hott•ls no r permanent 

tweommochLtion:-> for tra1· .:~ at th e lfLke hu t during Augu:,;t :tnd ~ ptcm h r, tb 

most fa1·orab l m nt h · for vi:;iting th lake, temporar ·ace mmod<ttiom; :;honld be 

pr·o,·ided and travel encouraged. 

EXCC'R 'ION ' \BO ·r RATlW L E'E. 

By fa r the mo:->t imprcs.·i1·e and to the geo l g ist, mo:-;t import. nt trip n-bout 

Crat r Lak is by boat from Ea.6·1e Cove alorw th e west rn and northern ·bore 

of the lak to Cl two d · and Rugged r :-t r turn i rw l _,. wn,y of the crater 

·apping th11 ·indc r cone in \'\ izar d Island. I ean b made in <t day but may 

req uire hard rowing. The r ar pportunity of trav :ing n.h ut in tlw interio r of 

a volcano ·ould hardly b a ny thi rw e l. ·e than int n.-ely inte r :->tirw . Tb de · cnt 

by th trail and Tuis g tb .- hor e di:->c lo ·c the alt rnn,tely O \ ' rlapp ing sh ct 

of and itiC" J:.n·a and co ng·lom ra of which the r im is omr osed. These tr c cut 

hy d ike - a prominent on is at Dev ils Backho ne and small r one,.: oc· ur 1 neath 

Lln Ro ·k. om of th :e a re ande!-!itr, hut otb rs dacite. 1h g reat tl w of 

Llao Rock , ove r 1,200 f t tb ic-1 in p lace.· and taperin, .. ; to thin do·e,; on th 

ide ·, is dac it . Tt i · younger than the and . it s f the rim a nd fi lls an old 

valley. t Purni ·o Poin t lay r.· f p umie ttnd .- trE'ams f daeit overli I laty 

and . itc which wa · g la.ciatrd befor e tho dacites wor erupted and a CI two d 

Cov i .·e n tb infl owing dacite from Ru o-g d Crest a nd th ca1·e l-in laya tunn l 

to the northsvard. Th late:t flow of th rim is tl tuffaccou: dae ito along th 

north a ·t ere t from Pumi e Poin t to tb Win g la . .-, but lat r e1·e n than thi:- is 

the excell nt example of a little ,·olcano which form · Wi zard I.·land, with its 

cinder cone capped by a ped e t crater summi t, mar ki rw t he ,. nt from ·wbi eb the 

(' in der. were blown. F rom tb island }tnd the hoat the c.-ln.cial notch s in th 

south r,rn rim of th htke and tho claeite ow~ of Cloud 'np a nd th astern r im 

may h , cen to gToatest advantag-e. 

Th nro:·t in. tructi1·c lay's walk from th nm en.m1 ( 'amp l on map) hut a 

r ather ba rd on , i .. along th w ;.;t rn ·rc t to Llao Rock. G!acial , tri ce a r be."t 

eli ·play d a long- this portion of th0 rim. A ndesite .. ar e xpo ed all the wa to the 

Llao Ro(·k fl ow, which n ar the edge may be xaruin ed both ahovc aml holow. 

The intlow of Cleetwood Cove i. cl early v i. ible f rom a di:;ta nce, and a n ox ·cli ent 

view of th e ·r ·t of the Ca. cad Rang may b' obtained. 

'Iho · who may wish to make a camping trip around the lak a rc advi.' ed to take 

a ~1 k tmin and devote a number of day ." to the trip a. th di. taoce }\1' und the cr st 

of the rim iH ov r :W mil e.'4 and over much of t hr route tntl'<' ling -is difticult. Th re 
i,.; no definite horsP trn.il ftrouncl th rim, hut a [ mdi<'al pa('k rout<> . wi th <'Hmping 

pia e:> indicated b) number:>, ~ marked upo n th ~ mnp (Pl. 1). 

The canyon of 'un ' reck is clifl:icnlt to l'ro.·s :v its weste rn wall i" pn•t·tpttou:L 

Ncar th e notch the re i:; pastur ' and good ca.ntpino·, but low r down. wlwrc the trail 

et·os.·e. ·, f . d a ncl water ar s ·a rce. At Cnmp 2, on tho w0st fork of Sflnl Cn'<>k then' 

i.· plenty of both. Carnp 3 ha ma ny attra ct ion :-~ h sicl s th line firs n.nd l'l owt•r,.;. 

The great eliff · n.r in piring, ancl thf' ru.·tlitw of tntm<'rous little c·a..:cadC's g i' t,.; :t lif\' 

to this inclo. eel camp that is not to h found lsC'wlwr a.bont the lakC'. 

Th n:-;e cnt of thC' ea,.;t :-; ide of and Cr0 k 'any on is : tc p and :-;omewhn.t c1 i fli cnlt, 

but the fin e \'iPw.· of th lake from th cR .~ t rn rim in th0 morning· abundantly pft.)' 

forth' spec in.l exe rti on neces ·ar) to attain th 111. 

<.:amp -1: has ,;om pa:>tur and s now wate r. BPn n.th tit <' htrgr ·lifl's just north of 

the camp wate r wa:; ob~'l. in cd f r th a.nimal,;. T o th no rtht' a:;;tward a.bout· :l ntil s, 

in the lin of the canyon h ead ing at Cloud C:t[ , ar tine _:-; pring: a nd IL nl:-> adC' 50 

feet in bei()'ht. Thcr i: on:iderabl pn:tur bore, hut on the who! the place i:-; less 

invitinE; fo r camping than location:> close to th e re,.;t. Fr m thi,.; (':tn1 [ th d<>,.;<·c nt 

to the htke may ea ily h madt• nt th ' ",,·in e-gla,.;s"-:-;hap<>d : lid >f (T-rotto Cow. 

At the lw n.d of Cl 0twood Co,·e th0 c r ""t i,; \'e 1·y rugg cl n.nd ,., 111\' whn difll ·ul t 

to c ro:;;.; with animal,;, 1 ut cl. 0wh r c tnw I Rlong th northcm rim of t hC' lake i::; 

a;.;y. N ar th e foot of Reel 'o ne th ere i: o-ood camping 1>,- n :pring . \t many 

p int.'i :dong· the lower slop of th \\·c ·tc rn rim of t h lak thrr are fin e camp., 

ple nty o f gra ·,wood and wat r , but in th past the h cp ba,·e oTcatly injured th 

pa ·tur . n.r th cr . t c liff · and rough talu · "lop • make traveling- diffiru lt and 

lanrrcrou for animal. The e. y a nd safe but longer route li e· w -::; t f the clifl' · 

to 'amp 6, which i,.; th main pa.stur<' cn.mp of the r e)'ion, with 1ine wate r. 

• 

A T I 

THE GEOLOG\ OF R.ATEH LAKE NATfONAL PARK 

.T _ • EPI-I I L . D I L L ER 

ll 
• 

l 
CO\ T ENT. OF P\H.T J. 

Pn){t.'. 

Introduction .. . ... . . . . ... ..... .. .... .. ....... .. .. .. . . .... .. . .. ... . . . . ............. .... . . .. I I 

Ca cade Ran ' t' . .............•. ·- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . 17 

Limits_ . _____ . __ __ __ . . __ . .. . ..... __ . ......... . .. ----- . ___ .......... . ----- .- -- . ... ... . 17 

Fou nrlation ......... _ ... _. _ . .. . .. _ . . . ... . ......... . .. ... -.-.......... . ........... . . ... 17 

Eoc ne hi: to ry.......... .. .... . .. .. .. . . .. ............... .. .. . . .. . . .. . . ............ .. . . HJ 

:'.Ji C'ene hi: tory ... .... . . __ . __ .. .. __ .. __ .. . ............. . . . ... . . . ____ ......... ----... . :?0 

ni on P ak ____ ... ___ . ___ .. --- ------- ____ ____ . __ _ . . . . ... ----- .. . ... - --- -·---·---··------- :W 

Mount Thi ~u n .. . . . . . .... . . .. . ... ... ___ _ . ... .. . . .... . ...... . .. .. . . . . . . . . . . . . ... . . . . . .. .. . :W 

:Mount :'.fazama . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . :?I 

(j ne ral featur> ..... . ... . .......... ____ . .. ... .. . .. . . . . . . . . . . .. . . . . . .. . . . . . . . . . . . .. . . . . :ll 

Laya . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . :2:~ 

And e~ it e;-: ___ .. ___________ _ .. __ ... . .. ____ . . . . . ............................ . . ___ ___ 2:~ 

\Vatchn1an area . .. _ .... ..... ... _ ..... .. . . . . ... .. .. . .. .. . . .. . .. . .... . . -........ :1P, 

r t> k a rt>a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

:'.lun.·on Point. ar a. ___ __ __ . ___ .... . .... . .................... . ...... .. ... . ... . . :25 

Cni on Peak area..... . .. . ......... . ... . ....... ........ .. ..... ..... .. .. ....... . :l() 

Eagl , Craw a r a _..... . .... .. .... ..... ......... . . .... .. .. .. . .... . ....... . ..... '26 

Dut.ton liff area... ....... ...... . ..... . .. ... . . .. . ..... ...... .......... ...... .. 27 

Rentinel Rotk area . ___ __ ... ....... .. . . . . ....... . ... _____ .... ____ __ ...... __ . __ _ 27 

Round Top ar a.. ........ . .. .... .. . . ........ . ....... . ............... . .... . ... . :l 

. 't·cel Bay a rea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Z!J 

\Vi1.ar I I. land . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . :l!l 

Ande. iticd ik e. .. . .. . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . ... . :·nl 

Ba,.alts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . :-;1 

Timber rater fl ow __ .. ____ .. ___ .. _. _ .. __ .. __ .. . .... _............. . ........... :;2 

De .. ert Cone an 1 R d Con flow.J ....................... __ ... _ .... _ . .. . . . _ . . _.. . DZ 

Bald 'rater fi ow ....... .. ..... . .. .. ........... . . . ...... .. ... . ....... . _.. . ..... ~ 

rater Peak flow _ . .... ... _ ... . _ ~ ______ . __ . ______ .... _ ..... _ .. _____ . __________ . ~ 

Oth r fl ows ..... . ... ....... . ... .... ........... __ . _____ ________ __ ___ . ___ ___ ... _ ;H 

Dacite;-:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . :H 

Run re k fl ow ...... .. ..... ... ... . ... . ...... : . ....... _____ ________ ___ . _ . .. _. _ :)i) 

( 'l•>ud ap fl ow . . ... . ... ... .... . ... ......... . ... . . _. _. _ .. _ . . ___ __ __ _ ... _ .. _. _ _ Wi 

U rou.·e U iII f:l w __ __ ___ .. ___ . __ .. . .. _. __ . . __ . _____ _ . . _____ .. ____ __ . . ... . _ _ _ _ _ _ :)(j 

Llao hock fl ow . . . . . .. .... . .. . ....... __ ...... . .... ____ __ ____ .. _. __ . __ __ __ __ .. J6 

\\'i n ria fl ow . . .... ---- -·.--- · .·- --. -- ---- -.. .. -.. - -.- -- -- -- ----- ------------ ;-){ 

Uleetwood OY fl ow .. ... . ... . ... .... . .. .. .. _ . .. ...... _ . _ ...... __ ... _ . _ .. _ . _ _ _ :-l~; 

Daeit ic dikes ... . ... .. .. . .. ____ .. . ...... . ....... _ ... . .... _ .. _ .... _. __ .. .... ... 3\) 

Dacitic pumice ...... ..... ... ... . __ . .. .. . .... . ... . ... . ...... _. ____ ._. 

13 
14 CONTENT OF PART I. 

:'IL unt Mazama-Continued. Pnge. 

Tlaciat.ion ................ . .. . ...... .. . ....................•.. . .. -. . . . . . . . . . . . . . . . . . . . -!1 

Original condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 

Development ................ .... . .... ............. . .... ...... . ... .. .. -. . . . . . . . . . . . . . . 45 

Destruction of Mount Mazatua and formation o£ the caldera... ... . . . . . . . . . . . . . . . . . . . . . . . . 46 

Crater Lake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 

Temperature ..... .... . .. . .......... .. . .. ...... ... . ... . . . ... . . . ... --.. . ....... . ... ..... 50 

Changes of water level ....... .... ......... . .... . .. . ..... . ...... .. . . .. ... ... ...... _ . . . . 53 

Evaporation .. _ .. _ ....................... . .. . ... ... . . . .. ........ . .. ... ..... _ .... . __ . _ . 57 

Inflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 

Outlet . . . ..... . ...... . ............... .... . ...... . ..... . .... ................ .. ...... _. _ 60 
T L 0 r JN p RT I. 

Pngc. 

PL,\TE 1. 'l:ap of rater Lake i\ati nal Park .. . ... . ....... . ..... .. ___ . . .. ___ ____ . . ........ .. 11 

I J. one · on summit platform of a cad H.an , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l 

Ill. . 1, "nion Pea k; 8, Rim of rater Lak ae o~ can~' n of \ riua Creek . .. .. . .. . . . ... . 2 

I V. Panoram.ic view of rater Lake .. . .. .. . .. . .. . . . . .. .... ....... . . . .. . . .. .. . . .'. .. ... 22 

V W tern bor ler of rater Lake, VictorRock to Llao Roek .. .... ...... . . . .. . . . . .... ~ 

VT. Geological map of Mount Mazama aud Crater Lake Kati na l l'a1·k . . . . . . . . . . . . . . . . . 2G 

\'IT .. 1, I nn r lope of +lacier Peak; 13, Ea tPa lisade . . ... . .. . .. . . ......... . . . .. . .. . . . . . 2, 

\"[Jl . . I, De,·ils Backbone; 13, Wizarl I laud . .. . . . . ..... . . .. ....... . . . . .. . . . __ . . . .. . __ . . :30 

l X . . I , Llao Rock· H, Flow of tuffac ous dacite e· t of P umi e Poin t . .. . ... . .. ... ... . .. 36 

X . . l, Valley ofca ved-in tun nel; lJ, leetwo d ove fl ow. .. . ... . . .. .. ... .. . .. . ... . ... . 38 

XJ. J ointed tuff of .\.nna r k --- -- -- ·-· ·· · · ······ · -- --------- --- ----- - ----- --- ----- · -!2 

XII. A, Moun t Iazama re tored ; B, Rim of Crater Lake. . . . . . ..... . ... . ... . .. . . . ... . . . . 44 

XIII. A, Water gage, rater Lake· B, Raft and mporating pan . .. ... .. . . . . .. . .. . . . ... ... 54 

F IG. 1. Map bowing route to rater Lake. . . . . .. . .. . .. . ... .. . . . . . .. . ... . . . . . . . . . . . . . . . . . . 18 

2. Thermometer and attachments used at Crater Lake .. . .... . .. .... .. . . . .. ..... .. . . __ . _ 51 

15 


S . GEOLOGICAL SURVEY 

"" nn '"' "'"' ... .... ,.., 1616 

, ... 19~, 

+70 "" f.11k, .~ rliu-. 

' 

, .. , 

-I 

\\'iznt·d ld . 1131 t::!.'J.<Ji ~c rtJ,n··· ... •tJl..-,yi19U 

.,. ~~~ I 

PROFESSIONAL PAPER No 3 PL I 

Sho ~ng lh ·· lot:nl.iti es. by 11111n bf'rs. wh r 1·e ~J)\'<'iiiiCll · werP tollt' ·Lc·d by J. S. Di lle I' ami d<·s ·riLed in th1 p•tpcr· 

S<;a l" 

- ---- Possible pack - t.ra1n route. but no tr·ail 

Camp locations numbered 

G ~} <~ i·,i:.'L~· 'ttil fiA and 

o· Tufl'll( (j ()U ~ rludtl) 

0 Dor ito 

8 Jlfi HII ll 

A l lyp ···~th<• ll <· ttndt·si l' 
Tl-!b UEOLOGY OF CRATER LAKE ~ TIONAL PARK. 

B.'· .) o:-;Jc i'JI tllLAI' D.t LL~H . 

Tbc geo logica l revord of thi. · cou ntry frou 1 t he ca rl ic 't pocb::; to the pTe' nt time 

i.· r eplete wi th ,·olcanic phe nomena . but tb ' d imax appea r.· to hav h e n rcncb ed in 

the ea rli er 1 ortion of th 1\eoeene . when o nr of the largu;t known ,·o l anit· fi eld:; of 

th e world ''' ft,.; vi(J·or ou.·J.v a ti,•e in o ur Northwestern 'tate::;. This area of vol<·ani 

a,cti,-ity :;trctc he · f ron1 the Hock:· Mountain::; to fh Pa ific, mbrucing n, larg 1 a.rt 

of \\ yoming, )[ ntana. Idaho, \ Va ·bington Orego n. tttld Califor nia. and pre ·c nting 

a g reat ntril'ty of \'Oie:wic ph non1rna onccr ni ng wh ich notwithstand ing a eopiou · 

li tera ur ' , t he re ha:< he 'n as yet but a ~mall an1ount of detail ed i n\'c. ·tio·ation . 

The ·rntral fratu re in the g olog·y of t hr "'rate r Lake ntiona l Pa rk i" the 

wrcvk of lount. J\lazallla . ~tnd in ord<'r to de.·nihe t hi:; more clearly, it i:o nect'::;::;a ry 

to on:;idt'r hridly tb o gr n ntl rrlation.· of the Ua~ntd Rang . 

' ~CAD I!} B.AKG 1<::. 

LI MITS O F THE CASCADE RANGE. 

Thr we,.;trrn limit of t hr g r 'at ,·ol ·anic fi.e ld is li kewis th e we ter n bo rd r of tbe 

!a:-'ntd ' Range . whi ·h ~ nl:tde up :Lt lrast la r u·c ly. if not wholl.\'. of ,·olea ni c material 

e rupted fn)lll :t he lt of n' nt,, e xtending fro n1 northe rn Uali fo rni <t to · ntral 'I'Va hinuto n. La" "<' n P eak marks th ' sout h r n e nd of the Cascatlr Han o·e, and Mount 

Raini ' l' !,.; ncar th' nortlwrn l' ncl . Beyond t bes peak" the old r r ock r i::.; from 

lw ne:tth tilt' m ng-e and forn 1 promine nt mountain ~>, the range it elf occupy ing a 

d ' pre::; ·ion in th ::;e old r terra ne::.; . 

F OUNDATION O F CASCADE RANGE. 

\. cl arl' r ('O ncepti n of th e drvrlopme nt of the Ca' cade .Rang-e mayb .ga ined br 

l'O nsid ring· the g-rog·ra phy of thl' rco·ion d nrino· the la.t r portio n of thr ' r ta•;eou::.; . 

At that time th<} roa:;t of nor t hl'rn California , Oreg·on, and Washington wa , ubsiding with r fere nee to sea lc ,·r l. ca u;:; ing t lw. ra. to advance upon the Janel. ln Cali · 

9.<.155- o. 0~--2 17 

• 
• 

1 GlWLUOY U.l!' CHAT:EH LAKE N TlUNAL l'A HK. 

fornia th e :;ea reached the we. ·tcm I a,.;e of the 'ic rra Ncntda and cu\'l'·l' •d :t hrgpart, it' not the whole, of th e Kla111ath Mutrnhtins. ln \Va:- hing ton it ht•at upon tht' 

wcstem ha;.;' of the range ncar th' eoast no rth of Mount Hainie r and in Oreo·orr it 

TIO 

~ferlf0rd 

DEA D 

SISHIYOU MOUNTAINS 

FIG. 1.-~ np win g route' lo Crnt r l.nkc. 
U. S. GEOLOGICAL SURVEY PROHSSIONAL PA~ER 1\0. 3 PL. II 

CONES ON SU MM IT PLAT FO RM O F CASCAD E RANGE. 

T he sharp P"Hk Of'\ the nght is Un1on Ptak; •n th ~ d•stance is Mount P 1tt ; in the foreground are W•zard Island and Crat<:"r Lake 

EO :E :E HI TORY Olf 'A' ADE HAN GF. . 19 

exte nckd f<tr into tlH' interior. )J a r in depo ·its of tbi · period O('l' lll' a long the ha ·e 

of th • Blue ,\lountain:; in r a.·tern Orego n, <1 :; th e '1'1. ' ·ftdc Range <lid not then rxist in 

Oregon to s hut out tlw 01 e n .·ca from that regio n. Ea::l tof th e KlaJnath Mountain ·, 

a:; :;how n IJy t hv po.·iti o n and d i ·trihution of t h ' C r taeeo u:; rock,; and fossil,., of 

Jllarin t' origin. th' ope n ·c;L <.;o nncctcd di r ·tl~· with th e ;;ea in the C'5anam •nto alle '. 

Th ' Casn ule Ran.u· th roughout a. larg part of it:; exte nt r •:ts upo n C r tac:cou:; r od.-,.:, 

:u1d is as;;o<: i<ttccl in OroQ'Oll and Califo rni a. with a d •prc ·io n .in tlH' o ldC' r rod~s 

hdwt•e n th e Klan1ath :Mo untain:-; o n the o ne han d and th' l~lu e J\lo untllin.-< and 'ic rm 

Xt•ntcl<L o n tiH' other. Thi.· deprc:sC'd :trNL be neath the lav;l.r:; of th e C<ki ·adt• Rnng 

n1u,.: t not J,e regarded prinmril.\· a · a. r egio n of sttbside nc c, a: it.o; chit•f lllO\ lll c nt I 

:; incc th e Cn•ta('t'O u;o; ha: b 'C' Il upward. ahOH' tb c :;ca. Th K la nmth and Blue mo un -

tains, as we ll a;; the 'ie rra N · vad<L, b owe \·c r , h:tn' hcP n •lC'Yat •cl ,.:o lllliCh m or than 

tile base of tb e Cascad Range th<tt it would app·ar o n th • .·urf<Lce <LS a d 1r ·'lOll 

\\'CI'C j t not fi llC'd with Ia n t. The depressio n i;c; so de p wlwr tb' Cas ·ado Hang-t' i;; 

cut ano,.;s hy tbc Kln111ath and Columbia ri\·c rs that tb c hottom of tb ' hwas for111 ing 

the hulk Jf tb c nuwe i: not rea ·bed. Jlo \\' \'Cr. at th e end · of th range th olde r 

r ocks ris to form a n1 or or less c lcn1tcd ba:e fo r th ost' part.' of tb range, a nd ~Lt 

1\lount Shast:1. as well <l'> o n til ' di\·icl e hctwcnn the Rogn e and [Tmpqua river wb •r c 

<Lil :u·ch of tlw olck r roc ks 'Xknds no rt heaste rly from th K laJnath 1\Iountain>< toward 

tbC' Blu l' 7\l o un tains of ('ast I'll Oreg·o n th e 'as ·ado Hang gets :;o do e to tl1e western sidC' of thl' d ·pressio n that the la nts iap up O\'Cl' th e arch of o lder r oc.ks rising to 

the wc>< tW<LI'cl . ,\.t \'ari o us points of th e ntno·t• gmno litic l'Ol'ks. ,.:u ·h <Ls ga hln·o and 

clioritC', oec ur; hut. th(' deep e rosion at the." . po in t.-; may havt• e~whed th' gra no li t <.': 

t·oncsponding to th C' htl' a,.: of t bt• uppe r p rtion f tb • rang·<'. 

EOCE N E HISTORY O F CASCADE RA N GE. 

Th c rC' can I> ' no n•a ·onah le <lo ubt tbat fos: ili.fcr o u:; 'rota· ou>< ro ·ks of 

marim• o rig in an' wide l.1· cli,.trihutcd .be neath th C' Cnscad c Hangc fron1 Las><c n Peak 

Lo th C' Co lnmhia, and that d uring tbC' C hi co epoch th whol a.rea was be n ath 

till' st'a. .·\.t I lw (' lo,.: o f t he 'rdne o us. illlporhtnt \.· hanges O<.;(' LI JTCd in thE' d istrihtt t io n of land and .seu. :\o rthC' rn Califomia . as we ll a::; so uth e rn OtC'go n. wa 

misecl nhon' tl1 e ,.;ca t'Xet•pting tlw Coast Hang reg io n no rth of H.ogu<' H.i\·er , 

w!Jit"h rC' Ill<tinpd beneath t hC' Sl'H during th 0 early part of th e T rtiury. The 

nwrin l' d <• posit;; o f t hC' J<:occ rw pl•riod in tb ' \·ici nity of H.ose burg run under the 

Casca IP Hangt', hut lnt\'t' no t yet b •n fou nd o n the ca:::tcrn side. Th co ng-lonl •ratt•s of th e Eo<:CIH'. lilu• tho:c of tb c CrC'bt ·eou , co ntain ma.n.r p ehhl c: of 

igm•on>< roeks, hut they ar of typ<'s commo n to th Klamath Mounta ins nnd are 

mn' or unkno\rn among tilt' ht\·a:-; 0 );p ;;; cl in the Ca-cadc RallO'<'. DuTing· the 

EoC'enC' t hl'l'l' \\'as vigoro us \·olc:u ni <' it('tivity " in thC' 'oa:t 1-L'l.no·c of OrC'gon. hut the 

~~~ nt cnth .\ nn. R<.'pt. r. G ol. Survey. Parl I , l 89ti. p. (15(i. 
OEOLUU Y OJ<' CJ{A'l'.J<:H LAK ~ N ATIONAL J'AHK. 

n.:Gord o f ,; uch :tdi, it~' ha.· no t Y t be n fou nd in the 'n:;mcl ' Hang •. That ,·olca noc:-; \\' ere activ alono· th e range durino· t he 11

:oee n i,; r •nd r •d lll ore prohahl e , 

al thOll).dl not .Y ·t beyond que><t ion, by Dr . .r. '. ;\[ rri~Litl' .· di TO\'l l' .\' o r Eo ·one 

,·oka ni l' ckpo.·it:; in t he .John Day r gio n. a 

MIOCEN E HISTORY OF CASCADE RANGE. 

The re can he no doubt ho wc v ' r, that lu1·ing th ":\lioc' nc 11 th ,·okano ':-; of 

th ' Ca ad c Hang' w ' re Jn o:;t ~tcti,· and the g- r atc r p rtion of th ' mng·l' wa,; l ui lt 

up. ~dthough it i:-; ' tlually ce rtitin that voleanil' al'ti,·it.'· ·o ntinuctl in th ::l ~Lill · 

n·~·ion lt a nuu1her of 1 oint.,; a lmo:;t to th e 1 r :->cnt tin JC. \\rhil e it lila\· b ::; urlll i:scd that the ''olcanoe: of th Cn ·cad Rang an' xtind. t he re arc IIHlll.\' .·o lf::ttaras hot ti pring ·, fLnd fu nnt i'Oics, ·bowing that ,-ol "til it ne rg y i:s not yet wholly 

d i:;;:ipatcd. All th p eaks of th "'as ·nde Range w r o nn' fll' i\·e \'ol anoes and 

from them came mo.-t of th e Ja,·a of th rat1o· . Ea h g-rC' n.t ,·o lca no Wit:-; >< IIITOund cd 

within its proYin('O, at I a. t during th e lut r : tagc:s h.'' nume ro us ,;nndlt'r ve nts 

fro 111 which issu •d th e !ant that fi ll ed up tit inte n r ning ·pace: and buil t up th 

p latfo rm of tb range. 

A ll of the g r eat \·obwoe. of th range p ro ba.h ly bad th e ir h g inning· in the 

1\lioee n . l\lany of th em, like Las:;cn P eak and \I unt 'ha: ta , r o nlinut' l thl'ir 

acti,·ity into th e Glacial cpo ·h, and hav suff red mucl1 rosi n sin ct' th e ir la,; t 

eruptions. In thi · manne r important ·tructurnl Jill n' n ·es ha\· be n broug-ht to 

1i g ht ::tmong t h [ oaks abo ut the h adwat r:s o f thC' mpqu:t. H.ogu . and 

Klamath rive r ·. and th l•sc ma\· I' no ted as t hro win g s0111' lig Lt upo n th histo ry 

of M o unt Mamnm. 

1:NlON P .I-:A K. 

nwn P ak (C' IP,·ation i.l-l ' L fc t) is on th ' ,;un1n1it o f th e 'asC}Ld e lhngc . in 

Oregon, about -u llliles north of th Ca lifornia line and H UJilcs ·outltw st of 'mt r 

Lake. It is a .·harp, ·oni cal pmLk (Pl. Ill, " I) ri. inu- about 1,·1:00 feet abov e th e 

g ene ra l level of the n e:;t ot to e rn.nge. About th e base upon the ea:t a nd we. t 

" ides, as we ll a · upon its ._ummit, a rc rclllnants of tb original tutf' ro nc but t he 

ma · · of th e peak expo:ed on all :-;id · is of so li d lan1. The molt n JJHLterial -dicl 

not ·ink away after th e tina ! ruption. Th ,·olca ni c ne ·k r c ·tilt d fron1 the 

lin~· o f la.va within th e cind r co ne in tb 

Union P ak to-day :-;how:-; u:-; tb no ·k -trip} d 

top of the ,·ol ·ani : rl 1ill1ney . 

f it: · cinde r ·one. 

MOC":N 'l' TlUKL 'EN. 

Mount Thi li:;en (ele vatio n 9, 250 f eet), the iVlatt rhorn of t he Ca cadc Rang , 

is 12 mil es no rth of Crate r Lake and ri · ~ about 2,000 f eet ~Lb~vP the g·cnPrul 

"Boll. lh·pt. (Jt·ol. l'niv. ('nlifornht, Vol. II. >:o. 9, p. :!S5. 

I>T I\'t' ll li ,•! h .\ 111 1. Repl. U. S. C: col. .'llr\'C)' , Pun Ill, 1900, p. :l2. 
U. S. GEOLOGICAL SURVEY PROFESSION AL PAPER NO. 3 PL. Ill 

A . UN IO N PEAK. 

11 RIM OF CRAl ER LA KE ACROSS CAN YON OF ANNA CREEK 

In the foreground is the canyon of Anna Creek, in the background Castle Crest is seen on tnc left and Vidae Peak on the right. 

MOUNT ~f . 21 

lc\·el of the er e. t of th ntng It is b uilt UJ! of hrio·bt-r ed , _y ello,v, a nd brown 

layer:; of t uft· int rbeclded ' vith thin sh e ts of hl.nt, an d i:; cnt hy a mo"t int \' c:-~ tin g· 

n twork of d ike:-; mdia t ing from th e c nter of the old Yo k ::tno. ?\o tra ee of a 

volcani c neck i · pre ·ent- t be peak is bu t a r 'mn:tnt ·fuTed o ut of tlw lctnt a.nd tnfl' 

co ne stnTonnd ing· the ,·ent . Afte r th fin al rupti on the m olt n ma.te ri a l with d rew 

from th co ne befor e consolidation, so as to 1Nw e no vo lcani c nec k correspond ing 

to th <tt o f U ni o n P e::tk. The su b. ide nce wi t hin th e chimn ey of Io un t Th ie l,.;e n 

afte r eru p ti o n n1u:-;t hn,,·e been o,·e r 1,000 f e t , for t he Hheet · of ln,·a e ffnsed 

from t hat ,·p nt r e:tch mo re t h1tn 1.000 f ert nho vr t hP exposed t hroat of t h o kl 

volcrw o. 

~10 UNT ~1AZ ~IA. 

On t he 1'1 111 of 'ra te r Lake t he re oncr ;;tood a promine nt p nak to \Yhi h t he 

name ::Vlo un t Ma;mn al has heen g i,·e n. Mou nt Ma:>.am::t i:; p r nctit<tll y nnkno wn t 

t he p eo pk of O rego n but th ey a r<' familia r wit h Cr ater L a ke, whi ch oce upi " th e 

depre.-. io n t hat r e:u lted from t h wre k of the great peale Th r rr mna nt o f 

Mo nn t Ma:>.ftma is mo t read ily identifi 0d w h · n refr n ecl to a . ..: t h .. rim of 'ntte r 

L [tke . ' The wrecking of ::VI oun t. Ma:>.ama wa::; t he cr ownin o· C\'E' nt in t h Yolean·ie 

hi::;to ry of t he 'a:-;cach' Rang-e, and r e ni t d f rom a mo \·e rn ent :-; imila r to thn,t just 

notre! in ·Mo unt Thi L··e n uut nu:~t y g r eater in it.-; . izr a.nd eo n-;eqnE' nc ~. This 

,·olrn ni \· adivit.\· enlmina tE'd in thr d0,. Jopment of a gn'at pit or n1 lde ra, wbi c· h fo r 

g ranckur an d bran ty rind :-; anyt hin g: of its k in d in t he worl d. 

GENERAL FEATURES. 

Tlw 1'1111 r nC'irc ling C r:ttcr La ke . whe n :-; e n from a di ,.;tancr f rom any f;:ide, 

appear::; a,.; a lnw ll dust r of ge ntly ,.;l opino· p a k.;; ri ,.; in g tbo t 1. 000 fre t above 

th gene ral ne t of t he range on whi c h t hey sta nd . A g od viE' w i. o bta ined 

from t he road a lo ng· .-\.nna C r <'k, wher e t b south ern po rt io n of thl' rim HPJ car,.; 

as .--; hown on Pl. 1 II, 8 . He re 'n,.;t le Cr est an d Vidae P a k ftre t he most promine nt 

fea.tun's. wi t h tbe c~wy n of A nna C reek in t he fo r g ro und . The topographi c 

p ro n1inr 1wc of nn t lvln:>.amn enn IH' rn o r fully reali zed w he n it i:-; co nside red t hat 

it is d os<' to tb c head o f Rogu , Klama th. a nd Umpq ua riY rs. Th e:-~c arc tb e o nl y 

l:trge str0arns breaking thro ug h th e m untain · to t he .·ea between th r 'o lumbi a a nd 

t.. h{' 'ac·mme nto, a nd t he ir wa te r ·h d mig ht be exp ec ted t b<' tlw p rin c ipal peak of 

thP C'a>;cade Rang -. 

T o o ne a rriving h.r the road at the ·r st of t he rim, th e lake in all its majestic 

he~tuty (P l. IV) appear · ·udd nly upo n the :cene a nd i::; profound ly irnp res. iY e. 

Thr eye behold:; 20 mi l s of unbrok u ·]iff ·, t h mn tn t o£ )1 un t aza a, 

rano-ing- from ove r 500 to n a rly 2 000 f t in heig h t, e ncircling a cl ep. blu e s hee t 

of p lac· id wate r in whi ch th r mirror 0cl wa ll:; ,·ie with th o . ig ina l slop e,; in ln·illi:l nc\· 
22 GEOLOGY OF ('RA'l'F.H LAKJ<: A'l'lONAL l'AH K. 

and g reat!.,- nha ncc thr d p th of t he pro. ·r cct-. Tlw la in' i>4 aho ut +! m ii Ps \\'ide 

and 6t mil e:; long . with a n ar a of nearl y 20t sq uarr milr>4. 

F rom th r \\'Oodcd ;;Jop r :t ,.;ho rt d i:.;tancr \\'ithin thr ri1n at \ i ·to r Rock :tn I'Xn'lle nt general ,·i \\' of thl' htkl' ma.y hr o!Lain d. The first po in t to nttl-h th P eye i · 

\Viza rd l ·la nd. lyi rw near ly 2 mi le'.' away. tH'<lr the western nmrg in o f t he lnk . Its 

irreg-u lar wPste m edge and thr :;tccp but synm1 ctri l'a.l trnneatrd o rw in the ·a>4tr rn 

1 o rtio n a rc Yc ry ;; nggestivc of \'Oica ni o rig in. W t' ·nn not. howc \'01'. in d ulg-e ou r 

fir:;t irupnls to o·o at o ne<' to t he i:lan(l, fo r t h n rri o us fra.trrrr,; of t h<' rim a r<' of 

gTP<tter impo rtanr·r in unra \· lirw t he C<trli r stHg"<'H of its g·cologi<"ul hi:-;to ry . 

On the ]('ft i,.: tht> w ste rn bo rdP r of tlw la kt> : hown in Pl. 1\r, with th e' W atc·hma n. (+la('i ' I' Pra k. and Dr ,•il,.: Bal'kh n opp ositr \\'izarcl h-:land. and Llao l{oek 

beyo nd. The:-;<' fraturc ·, with icto r H.oc k in th fo r g ro und in:-;tend of the \Yatrhman , a re nruch mo re clen.rl . .- hown in P l. V, f ront a n ex · ll ent phot graph by :Mr. 

Cunning ham. On t he rig ht. i:-; th e :;o uth rn bo rder of th' lak . ('a:;tlr 'rp:-;t. Ken 

t('h , 'cott PPak t:lcntin 1 Boc k. and 'loud 'al a r pear in tb(' clistanl' a long t b 

nnt. The ho ld :-; t pa rt of th :outbern rim i:-; cut off fr 111 thi ·· ,·icw h.v 'a,;tlt' 'r :-;t. 

A mo re compl te g nc ral icl a of 'rate r L ftk c <111d it:-; srrrround ing,; may he obtain d 

from t be map, Pl. V I. Th e broad . g nt le nt r ,;lopl\ with an inl' linatio n mngi ng 

from H) 0 to 1.- 0 , i>4 in .-tro ng ('O ntmst with thP ahnrpt inn<'r sl p<', with il,.: many 

difts. Thi,; difi'r re ne 1s ,,·e ll exprc ';; d h.v the relfl.t i,·e po.-ition of tlw ('Ontnurs 

in tht> map. The ,·o rtica l intr tTal of the <·ontou r,; i. 100 fr t. n thr innrr ,.: lop<' 

t he co ntonrs a re c rowded ·lo:-;e togcthrr to s how an i n ·line so st cp that one nerds 

to tmv 1 but a ,;ho rt way to de;o;ccnd 100 fcc t, ll'hil e on tbc oute r ;.; lo r e the ('O n tours 

a rc so fa r ;tpa.rt that o ne need,; to tra\·d a c n:-;iJ<'rab lp p o rtion of a n1ik to de :(·Pntl 

tbc same d i:;tanee. Tbe ou t r >dope at all poink; i:; a way from t lw htkc : and a,.: t h 

rim ri. e · at 1 ast a thou ·and fret above the g n ra l lev 1 of t l)(' e r st of the nlllg<' it 

is \tide nt l.v the basal po rtio n of a g r at ho ll o' con in wh ic·h the la ke j,, ·ontain r•d. 

In addition to th e stro no· ontrast h tw e n the o u t rand inne r !'! lop s o f li P 

rim the map shows tlr <' otc urT ncr of a nnmber of small cone: o n the 'out r ,; lo pl' 

of the g r eat co ne. Th se adnate cone: hav0 peculiar sig nifi eancc wh e n \rC' <'O nr r 

to o n:.; ide r the ,·ol ·ani ' rock.- o f w h i<· h t he regio n ~; comp sed. · The ri 111 is 

ribbed hy ridge a nd spur: radiating from tbe la k , ftncl the hPad of a ·h s pur 

is marked by a prominc n o n th e e re. t of the rim. The \'a riatio n in the a lti tud(' 

of the rim TCl't i.- 1,460 feet, with .-ev n point .. · rising nho\'1 , .0 0 fc t. Tlw 

c'l' : t gene rally is pa. sa.hle, so that a p d . tri;tn rn a.y fo llow it cont inu u .. l.\· M'O und 

tb la ke, with t he exception of sho rt in tcn ·a l.- 0 11 t he south rn siJ wh e re th e 

,.;hfLrpest p o rti o n of th rim occur. in astle 're;' t. H ma ny point ar ou nd thC' 

rim of the lake t~ b est r out i. o n the inne r : icl , wh e re th op en slo p<', genera lly 

1ve ll ma rked with dee r tra.i ls o \· r I cd.- of pumiee . aJI'orcl .. a n unolmtructcd vi w 

o f thr maj e;.;ti · ,.; hE>et o f wate r. 

U.S. OLOC AL SU --------------------------------------------------------------------------------------------------------l PAOFES fOI'IoAL P£~ NO. 3 PL. IV 

C RATER LAKE. 

PAN ORA M 

LAVA S OF i\fOl T )f AZA}fA. 

Th bPst way to g t a compr h nsi,·e d e w of the ha,..:c of ~f ount Maz:tnlll i;; 

to tnl\·elltronnd tb er e;;t of tl1C' rim, hnt th<' ,..:trn ('tnr<' i,.; :e('n to g r ate,.;t ad ,·a ntag·' 

f rom a. boat on t he la ke. 

L AVAS O F MOUNT MAZAMA .a 

Th r <' a r<' th ree ty pE';; of l~t,·a,.; in :vlonttt Mazama- ftnd .··ites, dac ites. nnd 

has:dt:-;- and t.h ir ftreal d i:-;tri hution ii-i repr ·ented on the :tc·1·ompanying map 

(Pl. V1). Tlw immed iate rim of t h lak is made up whol ly of :tnd ,.; itNJ ftll d 

claC' ite:-::. chid ly tlw fo rmer; t hE' ba,..:alt · ar lim ited to th e ont<' r ,.; lop<'. 'L h .r en nl <' 

from the ,..:mall <'r vent · ar ou nd tb ba::;e of th e larg r co n . 

Th theory of magmati c. d ifl' r ntiation ::;o ably advoca.ted hy Prof<'s:or Ieidi ng-;; 

and othe r,.: in th i: country to expl a in diti'<:> renc(';; in lavas <:> ru pted f ront th <' same 

vo lcani c· cente r. acco rd;;; we ll wit h thE' cour of C\·ent · in 1 unt ~lazama. It. 

e rupt io n:; beo-an with a nd lotw continued to h C'omposcd of lltva ha ving int rm('-

diat(' t'Otn po.-; it ion. Thi;; la \'a wa fo llow d tir.-t hy i<'s" sili eo n,; l;wa. t h<' lm ·nit 

f ront a numbe r of small nmt· on th<' tl a nks of th g reat \'Okan , and tinally h.\' t he 

chl'it s, whi ch elo ·ed the petrooT:tphic cyel . [tis possibl<' that th ba.' alts a nd dal'ite;; 

may have hc<' n in part co nt 1111 oraneou . but lw last <'rn ption from tbP. g rNtt moun -

tain wa.'l f chwite . Th n eamc the OT('at <' ng-ulfme nt. a nd <L new pctrogmph ic yc l<' 

h C'g<ul wi t h th e n.ndesit<' of Wit:anl Isla n l. 

\nd<'. itrs nsti nt<' hy far t he g rNtte r p ortio n of th<' lava of Monnt Mn.7.ama. 

A roug h estimat ma kes t he ir vo lum€' at 1 a t te n times t hr combitwd ,-olttmc of tb 

dacit<'s a nd ba ·al . The) form a lrno t t he whol of th<' inn r slope of the rim, 

where the O\' rlappin o· s h e ts of : u ce ·s i, ·e tl ows appeH.r i n ·e<;tion in the ir orde r 

of e ruption, fr om th cadie:;t to t he ate t. Fl ow.- lying at a depth of nearly 

"",000 f e<'t hen<'ath t he moun tain e ar " en, but a much la rger amoun t of tl ows 

:;till dcqwr i:; unexpo ed. W er it r o.sihle t r emove th e wate r of t lw la.k . t he 

thi ·k n(';;.- of th e expo:; d lava would he ne.-'trly doubled, and ther <' i ' no vid ne<' 

to show that it: character is ve ry cliff rl" nt from that whi ch now outcropR by tlu• 

wate r':; edg a round the lak<'. llowe,·e r at still g reater clC'[ tb:; thl" r e probably occur 

T rtiary a nd Cretaceous :-;ed im nts r ting on olde r rock · ·imilar 'to tho e of the Kl amath Mou ntain . Ho rn blend<'- a nd mi ca.-an<.le. ite.- wh ich are l'Ommonly as-·oe int·ed 

with the hyp rsth n -a ndcsit('s f the g r at ,·olcani c center · of the a cad€' Ran o·--

ft>' . fo r exampl , L as.- n P eak Moun t h, ta, and Mount H ood- have not been fou nd 

Th ~ rod.- •re~i m n coll c~ cct in tho vi ein it)' oi C'I'H tCr L>tkc httvc be ' 11 stu<licd by Prof. H. B. Pntton . nnd '"''' 

descrilPtl in d~tuil in the second ptlrt of t.hiM pnpt•r. Tht.: 11tt1Jibl.'l~ u~cd in bot h pupers refer to the :-Hmc c·ollet.:rinn . 
24 GEOJ.,QOY 0.1<' C"RATER LAKE A'J'lONAJ, l'AHK. 

in :Mount Mazama. Tra e. · of hornbl ende we rC' ob en 'rd in only two of the h~

.·thenc-andc ite oll c ·t d; on of these iRa ma:-;. iY :< bert nrarl y 100 f ct t.h i k nl ng 

the trail near the l oint wh e re it hegins the lese nl to t IH' htk (+±)." and tlw oth ' r 

i a. gray lavrt (±5) on th ·lop of Cast! Cr :-<t. 

The old t fl ows expo ·eel on th southwest :-; icl <' of th e lak<' are rcpr<'sented h.'· 

specimen. No . Z.J., 61,11 and 16:3. They arr o\·crlain hy many str ams which suc·c·rs-

·ively is ·nc land :pr ad from the sum111it r upp r 1< lopes of ;\f ount ~[aznrna. Tlw 

flows vary g reatly in . iz and numbrr in cliff n•nt porti on" of tlw rim . Tn plaers as 

many a. 30 sup rimposed htyer:<, mixed with many h<'ds of fragmrntftlmatrrial. makr 

np the wa.ll of the rilll. The largest numb r of flow:< <'xpose<.l in on<' sretion Ol·c·urs 

rtbont Sun 'r ek ot h. Mnn,v fiom; arc 00 to .J.O 1'<' t in thi('kn rss. lncl<'r 'HAl<• 

Crest nearly n sco r rtpp ar in thi:< steep slop , and they mng·p h o111 HO to '0 f eet. in 

thickn e··:. Between nHtny of t hem arc layer:-; of ,·okani · <'O ngl onwmte which <tre 

u:uaJiy thin, rtncl, h ing s fte r le:s prominent. Tn th w stern rim tlow:< arc not so 

numerous, and co nglomerate WfL e ·timat d to form }1 bout one-fo urth as large rt 

mn,o.; · as the :olid lava. ;viorc fnwm ntnl 111~1t .rial app ars t ha'' a. ·compani ed th<' 

earlier than th e later flows, rtnd n the wh I th r <' is a largN· proportion in the rim 

flt the hertd of Annfl 'r eck than el::; wh r . ln th Ea.-t Pali:aclr (Pl. \'II. H) tiH 

thicke1<t flow of and ,'tt i: w II exposed . lt is ('Ut hy mnn,v j inls. rPaC'hcs mor<' 

thfln halfwny from th water to the <· rc:t of th1 nm. ;lnd has :t thi<"knr s~ o f nParly 

500 fe et. 

The thickne:s of any flow npon th mountain slope depended ('hi<'lly tq on th r 

amount of Ia a, tts liqu idity, and the in ·lination of the urfae e o\'e r whi<·h it fiowcd. 

Many of th sheets are uniformly thin. They fol low the out<'r slop1• for <"On~idet·able di. tanc . and indicate l'L moderate su pply of lavn that tl ow<'d Pasily. Oth<'r 

flow:, as that of th Pali::;acl s, fill ed nti i<'Y" in th out r : lop f ~I unt 1azama 

and varied oTeatly and abruptly in tbi knes: b coming v ry thin on th ir edges. 

The thicke:t of all th e fl ow .. howev r, is tb o-r flt da ito flow of Llao Rock which 

is over 1,200 feet thick ov('r t he middle of an old valley . Th materi al was \' tdentl y very much less flu nt than the and site. , for the ·fl ow, n.ltbough thiC'k ts s hort 

and l1fllTOW. 

In di:tribution the ande ite . on the onte r : lope of the rim ru·c divid d into 

ten rtreas, flncl each may b de:ignated by :ome contain d featur , a: Th \\ a~ hntan, 

Cn:tle Creek, Munson Point, Union P ak, Eflgl Crag ·, Dutton Cliff ' entinPI Ho ·k 

Round Top. Bear Cr k, ,tnd teel Bay. All these area::; ar prn ti cal!.'· joitwd hy a 

complete ring of rtnde, it expo::; d upon the inn r : lop of the rim of the la.l<f' . ln 

addition to the e a reas around the rim i Wizflrl f.- land , which i. al >;o compo: d of 

ande:Jte. 

"The rock col lccuon to whi ·h the n11m bors ref •r i< in the :\:uion:ll ~lu "cn , Wit.•hlngton, D. c. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 3 PL. V 

WESTERN BORDER OF C RATER LAKE, FROM VICTOR ROCK TO LLAO ROCI{ 

LA V A:l OF MOU 'J' MAZAMA . 25 

1b <tl'C<L of whic·b The " atchman i:s part co ntains rt numher of ;:;epFLrat fiows 

but upo n t h map they are not di ..:ting-nil'hed. Th .'· ar ' parti cuht rly wcll l'XpO!'C'd 

hy nume rou · clifr , but in much of thl' a r n th ey arc cO\' r0d h.r ~: inl nmt rial. 

Although the 1iow: <tr much alik wh n ompar cl with om' nnoth r , thor ' i;; <·on. icl-

<' rnhll ,·n ri ati n within ach 1iow. 'I he b lo rystallin e g ray f rms. like No. GO. pas · 

in to the typ like o. 6- clark p rou ··, soft, and crumbly hut ri h in amorpho us 

lllattC't·- and No. 26, whi ch i cl ccid dl.v ,·itr ous. Th ompo. itC' charact r of the 

fi ws ma,y h best.<' n upo n th e inn r ;;lope, whe rC' Htf' ir sC'c tions an' C'xpo. eel . The 

nncl :-~ ites arc g nerally g- my. and may h e r edcli h. Th y a,rc sC'ldolll !V vitrC'ou:-; as 

o. 26. No. 60 has a dN.: id d ly p laty .·truct urC' , wh iC'b i,; loc:a lly wC' ll mrtrkC'd , 

a lthough rthsc nt at othl' l' po in t-;. The p la,tes a,rc u:-;1,ally <thont o n -half in h to an 

in<·h in th ickn s. <tnd stri ke' ?\. 7()° K nca,rl.'· prtnl ll I to t hC' spur, with a di p of 

2:'i 0 vV. Th th ickness of thr p la te's a t C' aeh o uterol i" ratb C' r uniform, but it 

va,ri . h tw e n tb o u terops. 

At The \Yat ·hman a nd Gla i r P eak the la,yr r:-; of !ant h<t\·c a de id d upwa rd 

LUTe wh n v iewed fr m th e lnkl:' , an l suo·g-est t ha t th e volcani c \'C' nt from whi ch 

th C' ]a,·a,' of tha,t 1 orti o n f th e rim issued was no t ce ntra l o,·cr th C' lak . hut much 

<· losc r to the wC'.'tc rn bo rde r. This ,-icw is fully bo rne o ut by the ebaract r of the 

ig·nC'ous mat ri<tl in G laciC' r PNtk. lt i:s e mposed in :-;mall part of da rker laggy 

andc;;itcs and mul·h r <'d, : cllow, or whiti,.;h frng me nta.l tnate rirtl whi ch i' highly colorccl, <ls if' l y th e csca.p of hot volcani c g a: . ncar the Yent. F rom the lake the ·e 

colo rC' d patc h · a rc brilliant in th . morning light. On the inn >r . lope f G lacier 

P a,k (P l. Vll , t) ar nnmcrou~ eolumn . on of whi h is o v r 100 feet high. To 

eall this G lncicr P eak i,.; a mi. nomer for thC' ,.; lac iati o n her' i · mu h l ss di. tinct 

tha n on the hills farther ,.;outh a lo ng th e r in1. 

STI. ~ (' ll E E K .\:-o' I> Eii iTE .\Il EA. 

On thc WC',.;tC' rn hordC' r of tlw rim north of a;;tiC' Cree k i a, hi ll of andesite 

much likP that a ,.;hort cli:-;t:wc:C> to the C' a,..t. front which it i: ;;cparatC'<l h.'· a I>C'It of 

g·lrt<' ial drift. 

For 2 mile· f rom th ·r ·t of the ritl! th diviclc be tween Castle and Anna creek · 

1. cover d l!n·gely by morainal material, hut ande ite fina lly crop out in occasional 

tiffs a nd giv e \·ide ncc of thc l'hara te r of the ro k b enca.th th ·urfacc d posit · In 

th Mun. on Poin t a,ren. A :-;omewbat da itic spe ·imen (79) from on of the rounded 

ledges oE thif' ar a wa · fo und by D r. Patton to contai n tridymite. To the :outh nnd 

:-outhwe:t, h yond th e mnin r oad. thi ,.; andeRitc i · o \·ered by a large Ili a,.;::-; of basalt. 
2G GEULOOY 0!-' ('RATER ~ KE NA'I'I O ' AL PAWZ. 

O~ PI•: .\J' :\X IH ::."\ 1'1' 1-: \HE.\ . 

Toward t h<' southern horde t' of' the a r a rnappl'd, ncar P ole 13rid o·c C r e k , i~ a 

mass of H.nclesit<' . forming ~l bolt!, rock.\' point, which has ilel'n strongly gl:wi~tt d o rt 

the .·ide toward Crat r J.,n,k . Tlw two types of and e:;it (4L and lOU) found l1Pre do 

not loo k e ntir 1_,. alike, yet t he rock · appear to IH1 tb s:tutC' . The fi r. t i- ande. iti · 

in appea.rftnc c an l the 'C'to nd somewhat daciti('. This is part of the large :tr a 

whi c b i,.; o utlin d fl, . including U ni o n Peak, uu t is l'l'. o·nill d HH ('() nta.inino· llllJ('h 

bnsalt. Although th e :-; umrnit of nio n P C'a k is hyp rsth n -;tndP. ite, th middle 

and lowe r slopes upon t he .a:;tcnt sid ;tr composed of lm ·a.lt. oc<"asion:tlly r ich in 

oli,·irw. Thc rc wa no oppo rtuni ty to nHtp the :-;(llrt.lwrn and ' l'~t rn !.orders of tire 

park in a,,- gTc:tt detail :ts th e other rti on~. 

The l:uc:e arl'a of andesite fo rmin o· tlw broad divide b twc n Anna and un 

crc ck,- i,- 111 ade up of nnw · pronrincnt :-;hcet...;. This is hc,.;t see n front Dutton ' lifL 

~ wb e n' th edge of tlw platfomr ''Pl ar~ unde r\ iclac Pr;tk, t.hc hi g hest I oin_t _in t he 

rilll of the la.k<'. Although tbC' ·tnr ctur<' i:-; partially o hHl'Ul' d hy :o; teel talu:-> ~, 

' nongh is ,.i ·ihl e to :s how t h<tt the rim i:s made tq of succ· ·si,·c Pc t~ of lava, whi ch 

d ip awa,y from the la ke ~tpp r xima.t-ly I fll'iLII c l to the pres nt :-;u rf:t<' <'. On the nppr r 

.-urfaec of thi ·_platfo rm l'xposLHC' arc few xc pting wher e tlw su rf<t<"C lay e r of 

sa.ncl and pumice i · r moved . 

. J n :-;trong co ntrast to the ea._ tern cdg is the oppo ·ite borde r of t.hi:-; pln.tfonn 

in Cast! 're:t, whi h 1.· rugcrcd, and so ,-hitrp as to h impa. sabll'. At th<' foot of a 

p r ciprtous wall a thousand fe<'t hig h, o n the no rtb .'idC' of this .·e rratcd rcl4 t. li e~ 

Crate r L ake. Th i i:; th o nly port10n of tb er e ·t that i:-; pnt ·tical! · impa ·: able. 

In th<' :-<umm it of Castl e Cr t the oTay a.ncle ite i:-; like that whtclr is mo:->t ·ommon 

about the rim, hut wa. · found h.,. Dr. Patton to co ntain a ,-mall amount of horn -

blende . th reby affording an approach toward hornhlcndc-andesrtc , whic·h ha s not 

y et hc0. n found ·about Crat r L ake. On the ntg-o·ed do·(' of 'a. t l ~t . toward 

Eagl<' 'rag ·, arc g-rC'at mass :; of volcani c cono· lomerate, .·uch a · arE' rare ly .x po,.l<l 

on the o ute r slop of th rim. hut arc common on th e inn er lope. Th ey frcq uPntly 

a lte rna te with solid shP ts of a ndesitP. and sometime· :Lttain lrtrg' dirnC'nsions, 

csp ec·ia lly in tlw :outbwe. t rn portion of th rim. Tb y a rc g n i·ally .omposed of 

fragm nts of ande ·1t , rich in amo rphous 1 mtt rand ofte n· dark r· r din co lor. n 

th divicle :south of Dye r Rock t here i. mueh mominal matt r and pumice. so that tb 

:olid lava · rarely o utc rop, but wh re th ey do they ar we ll g lac iated. 

Near the outhe rn tmtrgin of th e area mapped i. · ,Crater Peak, a hill of ha:alt 

r e ting on a p latform partly of ande ito Mel partly of clac it . The re lati ,·c ag<' of 

th<' rocks i · clearly s hown , and i.· furth e r demo nstrated hy tho fact that fragments 
u . S GEO LOGICAL SU RVEY 

Tr"UH' ~UIOt•On ftr10 Too(l rap.,'Y ~( t.l.H·k 6 Kerr 

~ . .,,, "O)'C\1 tn U~8(• 

l. _l Claf"ialnHtJ-;l iw·s nnd 

dncir" '"fr Gln <:in l stl'iH' 

''" ,,., - ,., '"' ,.,. 

"'" - 1616 

... 

, ... 

11Y , I. S. I >I LI.F:H 

s,·nJ 

LEG EN D 

liS> 

JULIU!J 6/f.N & CO LITtl N "t 

1/159 

, .. , lr.6 ("" ... , ... "-" 

, ... 11118 

H3!1 

c_.=__ J 

I lyp< ·r ·s th~n c- dPsi (• 

-- 0 Dt-wi tPdik's 

LAVA . OF MO l 'I' ~fAZAMA. 27 

of tb underl.\·ing nnde it<> were thrown ont during th e activity of the h:1Mdti 

c rate r. 

Gren t diit'. of andc. ·itc borde r S un 'reck Cany on in 1lac:e,.;. <tnd the rock 1.· 

w Jl xpo.wl a l,;o at the fa lls whe re "" un ' reek. at an altitude of about 6,5 0 

f t, leaYe · the hr ad U-. hap d \'a ll ey and plunge · ±00 f et o \·c r a ,;e ri ~ of a.--

c·ades into n sharpe r canyon eut in da ·ito. Tbi · line o f cliff · aero. >; th eour,.;e 

o f . 'un Creek connects the a ncl esites of tbr t\rO diY idr,.; cn,.;t and wf,.;t of that 

strt>am. 

Dl'T'J'O:-: {'I.I VI-' .\ N IH-:R ITic ARE.•. 

In the broad di,·ide:> bebv n Sand and Sun r eks an lr. itr play: a small e r 

part and shows but littl e n trin,t io n. Near the middle of the divide , at nn ::lltitude 

of about 7,000 fert, tbe re i an a nde::; it (76) full of secre ti o n. (\:J ). The andesite 

i: quite no r111al , but th inclusions are basalti c. Thr same ma,t rial witb s e retion.- oecur: in the form of large howld rs nca r by , and a short list.-'Lnte to the 

west, in on of the h ad gul hes of the ·w est F o rk f Sand ' r e k, it is overl ain 

h. <t d idedl phtty andesite (-27). imilar nndesit (;'50) full of se ·r tion,.; was s en 

near til<' ·cdo· of the wate r und r Sun ' r e k ;\otch. The nnd sitic ht\'fl:'l of th 

.-outh rim a rc much nl ikc c \·erywh e r , with th ex ptions noted aho,• , and rtrc 

rcpr e:rnted hy )l "· 50 nnd -!6. th latter from Dutto n ' lift'. wb crc it is mpp d 

hy LO fret of 1 umice. 

Sand 'r k, likr its n ighhor is hord r rd l y Teat cliffs, e p ecia,lly on tb 

west. \ : · ndino- th is c reek ne-hnlf mil south of th bk rim, T olleeted a 

h ttom. One hundrr d f ct lll N . 5 wa tak n, and 600 

f <•t fron1 the ho ttom f thl:' canyon ~ . 2! wa.- co lle t d, wbill:' No. 37 cam from 

tb to] of th hill. n this di,·id w I'C coller'ted tb intc r e tirw jected fnlgm nts (1-!7- 151) of da itic mat ria,l. About 2 mil · from the notch the ande ·it 

ha,.; a marked platy structmc, wbi h is cu rTed, i'howing b r ad : urface;.; and fold .. 

Farth r ,;outbrnst, nt an altitude of about G,~no fe t. the clitf' of ancle:ite (6-!) 

O\'Prl i<' dac i t . ~ u tr tb p contac- fr 111 w hi ' h a g reat spri no- is. ue. tbe and . it i. 

hl:t<"k , as if from thP prc;.;en · o l' tnul'h tun rph ous matter, cl ue to the ~mdde n cooling 

o l' till' undr r surface. -:\' r ar by is a ma,.;s f ,-e ry platy ande;.;itC' clo l.r a~ . ociated 

1\'ith t lw undr rlyino· cht ·ite. A Hho rt eli . tanr to the outhea:'t, upon th ame 

di,·id . the <tnd sitr CH) h ars thr same relation to unci rlyi ng da itc (127). Th 

ap1roximatr c·ontn t b ' twee n tlw two roeks mn.,- he tnt d ae ros to the cn n.vo n of 

Sun 'r eck. 

»E:-.'T ll\I( L 1!0('1< \ :-IOES!'l'E A I!E.\. 

On the lak slope of KerT Noteh i::: n vitreou:s nncl , ite, well jointr cl (16). with 

columns -!6.G inehcs t hi ck. This ;.;hr t of eolumnnr lnva clips f\Wfl \' fr-om thr lake 
28 EOLOnY 1<' C'HA'I'l<:R LAK t•: A'I' IO TAl. P ARK. 

and xpo. ed neftr th bottom upon 1 oth ,.; i C'~ I' Sand 'r(' k 'llnyon ncar the 

notch. 

From 'c ntinr l Hock ca,;tw:t rd to the ,·ieinity of Sc lt P ak i~ one I' tb laro r~t 

ar ea · of a ndc.-;itc, hut by far thr g rC'fLtcr I art o f it i-; eovc r<'d with pumie<' and ontrop ar · fe ,Y. c<:u~ na.l dift's and hugo fmg·ment,; of ;Wd<'~ tr OlTUr on t bc. t 01 

slope. ea ·t of Md 'reek Canyon, hut h yon I lw,.;e the ,.;udacc ~ gr n<'rn ll.r c ,·c reel 

with a layer of ,.;ma ll p umi c fragm ents. :-:l(·ott Prak is nhout I ,000 fret bighc t· 

than an) other 1 oin t in th ,·icini ty of "mtrr Lnk!'. ft wn~ onc·r an a<"ti\'C ,·ol ftno 

a.nd amono· its n ighh rs next in size nnd irnportantn to Mount ;\ht7.itt na. In fact, it 

mark>: the nl listinet Rndcsiti Yrnt of thi;; ec ntr r ou ,.; idP of hr princ·ip:tl one r p -

r s nted hy )fonnt Mazama. t~ lanl ~ spr ad to thP ca;;t. 1\Wfl.\' fr 111 tiH· lak ' for 

in tltr cntin I Ho k ~ect on of the rim tlw hLnl:< npp<'nr to ha,· flowrd W<';;tward 

from ti1C' .Mazama rente r. 

'cott Peak wa.· ontc a ' 11 -cldinrd ('J'atrr. hut i h~t,.; i><'en hrok n away upon tb 

northwe. t, and drains into the. 'outh F ork of Bra r 're k hy a broad ly rou ndl'd ntll y, 

wbicb looks af: if it had been cut I y g la ial ndi n. Th . ·I [ c. f tb m untain a.re 

generally eo,·er d with pumi , but he r and there arP fragm n ., of and .·it ( 0), 

and near th s ummit actual ledge>: C7) o en r. Th hwa i;.; 0' n raii.Y reddish or o-ra.\' 

(200), hut somptimc. o-r eeni:h (1!1 '). HS if C' nsid mbly nit red. ('('fl. ionally (-!) i is 

om<'what gla .'.\'. Both · os. 200 and -:1: W<'J'<' loose p i<'t<'s on th southw ,.;t sid f 

thccratrr. hut o. Hl was in pine . TbP quaqua\·(' ~al di1 of the . h ct.· of ,·ol·nnic 

mate rial ;;bows t hat . 'C'ott P<'nk wrv a nater, and t11C' 2 mil<'s f country int n ·ening 

hetween it and th e rim show,; it,; indi ,·iduality. Th \ hol a~pett of th rn ountnin il'l 

one of conside rable ag<'. and it i;.; c,·id<'nt that it h anw · xtin t hrfor th In" ntption of .Mount )1nzama . which >'pr<'ad pumi ce c ,·ervwh '!'e. n the ou ' ick th slop s 

are gentl e. hut w ithin th e CLli'V of th<' M •i nt ·ratrr th y 1u· , . r y >'te p, and th<' 

now l.oclged th r i.· I uta rPmnant of the g la ·icr that on stHrtcd at that point. 

HOl':'\J) TOI' A:'\llf;;<JTE AREA. 

The Hound Top area i,; simply a part I ft uncov red by two cia it fl ows on<' 

on rach ,.;id<'. a nd the o- lacial material to th<' north<'a ·tward. Tt mhral'CH upon th 

s urface of the rim two flow ·, fo rming promi n nt cliff. , th ru ternm st of whic·h is 

shown in Pl. V JI. B. The wc:tem palisade flow fi ll. a n old ntll y to th wate r's 

edo- , and, like it:< n<' ig bbor, has a thi ckne.'.· of OY r 300 f<'ct. 'I he Iowrr 10 f t of 

thi ~ flow ,<'· p ecially that of the a,-.:tern pali acle, wbe r it contr. · in con tad (I'/) w ith 

its bed, i,; g·la sy. 1t i.· much broken be low, ~t nd li .· in plac .· upon cono·lom('ra.t<'. 

P a rt: of it a re ,·er y platy, xccpting in the g la sy portion hE'Iow, and an imp<'l'feet 

jointed. tructur extend through th ma. :. ft t hin. out mpid ly on both sidrs to an 

edo·e, and i.- ov rlain by a thi n layer of tuf.fac ou da itc, a Jat<'r fi ow of ~ hi c· h 

appear at th · left in Pl. Vll, B. 
U. S. GEOLOGICAL SURVEY PROFESSIOP\ AL PAPER NO. S PL. VII 

A. INNER SLOPE OF GLACIER PEAK. 

JJ. EAST PALISADE. 

L .\\" AS 1!1•' ~10 NT ;\ .AZ \~I . 2U 

STEEl. II. I Y A:-; 1)1~'> 1'1'1 ·: A IO>.I . 

Th , area of amle~itc 0 11 the outer slope of th r1111 n' pn'HC' nb a large liow 

l'ro1n tb rim at f:)teel Bay no rth ast towa.rd Bear Creek. Like the Houn I T op area, 

it li e,.: betweln two later fl ow:;; of dacite a nd to t he north p~v::;c:; out of sig ht 

ht•ncath tb pumice plain. It is a typiea.l a.nd site (:6\J) a.nd mu<: b g lac iated. 

\ Vit.mrd Uand is a perfect!.'· pr ·e1Tcd ,·olt:ano eo1v isting f a ·i nd ' I' co ne (Pl. 

Vlll, B), with crate r " :tho\'e and I}L\'a ti cld about it;; l1a~e . \.mid :; uch imprc,;si\· 

surroundings it i:; one of tlw most attm. ·tiv a nd inYi t in o· ··I ot. · of tb re u· ion. T b ' 

!ant ~; an de ·ite a nd I e long-::; not nly to tbc Ia ·t ande:;ite 1iow. but to t he tina! eruption co nnected with tb i. oTeat ,·ol<:ani<' ce nte r. The bulk of tb old 1· hwas i · 

andesite ; th en come tb ' hasalts from tb co nes around t h ha ·e of th e rim, and 

th e drwites on tb mountain .·lope .-uec rdcd . F innlly , after tb g r ~tt cata tr opb 

wh ich e ng ulfed tb uppe r pa rt of Mount ~Ja za 111 a. an andcsiti<' e ru ption o n t hl li oo r 

of the calde ra fo llowed, whi ch built up \\'i za rd Island ~• d apparrntly (·o,·er d a lmost 

tbc wbol bottom of Cmter L akr. 

'v\ iza rd I. ·land ha. an a r ea. of nearly nin e-t nth s of a sq uare n1ilc. The ca.-te rn 

balf i,- a prominent t' ind r eo n , :tnd th e weste rn is an l' XtrC'meJy rough lava ti c ld. 

Thr ei ndcr eo nc ri. i no· from he Ia va tie ld has Yer,v st" p sl0pcs. mad up ·hi etty of 

frag-n1 nut.l nmterinl h lown out of th erater. :tnd ri ·cs to n. b ig ht of ±5 feet. Th 

emtPr in its summit is }lhout :4.-o f et in cli:un •t rand 80 fr t de · I. [ t.-; bottom is 

:,; lid lax:t. 1n ~id it.-< rim upo n the :;outhwc,·t ~-:lop is ;t g rcut ·now b~tnk. wh er ' 

the ,; no' ae ·umulat s during- t he win te r and la ·ts almost throughout the year. The 

lapilli are rathe r oa rs· :111 I u,.;ua ll y clark or hlnck. but many <tre r d. Th re arc 

num ·rOll. ' fntj!,'Ul l' nts f lava a nd l·ompamti,·c ly li ttle ,'a nd . The ·oli d la.n1 i,- bri lli ant 

red o nly upon tlw surffWC : \\'i t hin it i,- da rk. \\'hnn the ma t rial is I Ol'Oll i:l the co lo r 

may P ' t'lll 'ate the wh olr lllas,.:. One hundr d feet be low th ' summi t o n tbc nortbwc~t 

slope a littl e stn'n nl of la nt (~0) 6 to l3 fed in bi kn <'s~' hr k out a.nd cour cd down 

t b slop fo r 1:)0 f ct. lt·:; ,.:u rh tC'l' i" ,·rry To ugh and ,.;O ln c whnt ropy, and a lo ug tb' 

under sudae<' it pi ·kc'cl :wei inclosed numc rou:; frag· n1rnt"" from the slop ove r " ·hich 

it passrcl. 'Nell.!' t br ~-: unllni t. i,- a ma ,.:;.; of bri'lliantly red lava (. 6). The eone is 

the refore not wholly vo n11 oscd of r in d r,.:. but co nta in:;. h e::; ides lapi lli and chu nk" 

nThc Sll\l('(' t'•:O:hrlpCtl d •prt'S.'iillll in the ~umtnil of the ('indct'l'Ol'\(' or \Yiz.ard !~lund is properl y cttllcrlll {')'(l/CI'. It mnrk ~ 

un orilic·c ft·otn whi<:h h\\'H r('nrh('rl tlh' ~urfHcc tn Luild up thl' <:indcr cone rl nd Ju,·n field. rnm the fn (:t thAt the lnkc is 

('H ll t.•d Crntcr LakL· tlw t(•rm <·rntcr hm: brcn ttpplh.:tl to the gr<·nt dcpn~~itm whi ch th e luke occupit':o;. Tlu.' lnrge dcpre:·..:.ion 

docs not in it."~ prc:o:cnt !-:izc mllrk the orifkc frmn whit"h th e IU\' <t.."' of ~I unt i\l'n zn mn i:-:su('d upon the !-:Urfuc to l uild up 

tht' mounlltin. hut mtlu.:r, u:-> will hi.' :-:hnwn in til l• :O:t t)llt_ l. llh' IHlh• through whi ch tit(' Stunrnit of lht mounhtin :-:nnk i11to 

th(' nrth. GrC1tt ., pl'(~s. .. ion ~ lik (• thnt t•nntuinill1-:' \rnt('l' L11k c. (WiKinnting IJy :..;ul):-;it.lcn('(' ill ('OiliH'Ption with \'nlf'lUlil· 

1i l'livity. urc oftt' Tt <· ,dll'd pit f'l'ut 'I"!-', hut bdkt' :-:till ,·nldtra,"l, \\hic·h i~<li :o: tin ·th·c. Prof. \\'. i\1. D tl \' i..:. \'f"ry appr pri:ttl'i~· 

t! nutrk~ (PIIy"'il·tll (;\'OJ;I'ttphy , p. :! l:l \ thut th l' dl pn·~:-tic ttl <·orltllillill.l! ('rnh.•r Lnke i~ "Hil l' of the mn:-;t ~l i! h t·ul(h .. nt~ j11 

Lit ·' world. " 
30 GEOLOOY o~· 'HATEH LAKE ATIO A L I'A l{K. 

of hwa. a nutn hc r of small ti ows, 11 t o f s ufli ·i nt t-~ zt• . howt' \'t'J'. to intnrupt th ' 

rcu·ulari t,· of tltr cone. ar tltc base of the I'Oil <' . wltrr<' it tncrg' · into t h ' lava ,., . n ld, ·e \'Cl'a l .. volca ni c bu llrt:' ,. we re obs rv rd . They fLI 'l' rou nd, and l'ILilg'e in 

dhuu t r from L to 2 f et, with in·r •ndar fmcturcs. They appPar to hav .·o lidificd 

b fore ejection . like thos so w II ckv loped about th e has' or the ·imle r t'Onl' IO 

111iles north ·tst of La>" · n Prak. Ca lifornia. a 

The la.vn now whi ch ext nds wt•stwarcl i . ..; xtrc nH•Iy rough a11d lll:tcl ' up of laq..(·t· 

a twtda r h lo ks of tb hrok n flow. [t i.· a da rk. sonH•whaL lmsalti ·-looking a 11 rksitc 

(UJ), whi ch i · o · ·n ' iona lly strcakr I with lig ht e r co lo rPd natte ri al (:lO) a lllo ng th da rk 

band.·. The lant . C<q d (' hi n,. from t he IV :t has(' of th ·i ll d r ·onl' and sprt>ad 

w .tw<trd beyond tht• pre~e t limi t of thP island, fo r !)(neath tb e c l ' <LL' wat r it tnay 

b · n to extend far w :;t toward t h : ho n' o l' th lake. So111e es ·ap ed astwarcl . 

a nd it i. p robabl that lava front tit '\\ izard Isla nd r ntc r spr •acl ov r lllll h o f th 

floor of th' lake. 

The ea -tward tiow.· fL r I ·: hrok n upon tit • s urfa tt'. and an· probaiJi y o ltlt•r than 

th ·e to th e west, forth ."ILL' w •I] (;0 \' CL' 1 with tr ('S. T h now is w ll l'XP " d in 

·ection a long on of th .·mall streams on the rast ,; ho rr of tb i ·land . and xhibi ts 

to ~1 marked d O'ree an an·hccl platy struetun• parallt• l to th r ,; u rfaco of the fl ow. 

uch structur i · ntr on th • i.· land , but has h e n oh:-;c n ·ccl l'Urvin,. a ro un I the 

ntliTO\ nn d tbi k How,; of tb ,·im, ' ·iu ll y in UH· 11 •i d.1IJ rho d of Llau l{od\. 

A :-IJH ~ITil' Ill K ·~~. 

A ·ruise on th e lak r e~tl s tL llllllllwr o l' dikr:-: whi<.:h ·ut th <• nttt mdially. 

Eleven we re ohs tT d in a il- s vcn n ar Llao Roc k. tiH oppositl' . 't·utt P al<. 

and the r emai ning n a sho rt di.ta n c wr -t of Eag l • Cov . Nin of th 'Hl an• of 

ande>lite and two of dacit . 

The only promin nt d ik (Pl. Jll, .. 1) i: f and ·it. It ·u,; thruu cr h t he cn!irC' 

rim from lake to (.;l'e. tan 1 ta.nd: out con: pi ·uou:ly brtw n G la<" ie r P al twd Llau 

Rock. It ha be n named the Drv ils Ba ·kl one. Thi · pr minc nt dike i:-; nNtrl,r 

verti ca l and · trike: . 50° \t\ . f t nLri e from to :&0 fcc t in th il'knr:s a nd o tlset:-: 

n ar t he middle of th 1 pe. Th :ampl of this rock (!l±) wa" take n 0 11 t ill' n •st, 

a nd i n toe ma, · to the unaided ey , it rc:emb l .· oTay basalt morr than t he nonwtl 

a nde:itic rock of th e rim. On mino:co pi ·al vidence Dr. Patton rpf rK it to tlt e 

a ndesite:. lt ha. a co lumna r strut:tu re atro: s t h dike and fL I •ss l'O nspi ·ttuus 

parting n ttr th side · parallel to tb contRct with th e adja ·ent ro k. 

U nd r the ea: t end of Ll ao Rock ar two dik ,' 1 f which tlw t-~o uth •rtt o n , is 

r emarkable. I t fir: t apprars with a w idth of ~ f ct at th top o f a tnlu t-~ " lop tOO 

feet above the lake, nnd has a ,·it rophyri e bordr r. pwanl it thiekrns sli u· ht ly a" it 

~<.Bull. 1·. >' Ucol. 'un·cy :-<o. i9, , Pl. IV. 
U. S. GEOLOGICAL SURVEY PROFESSION.\L PAPER NO. 3 PL. VIti 

A. DEVILS BAC KBON E. 

lJ. WIZARD IS LAN D. 

LAVA 'l OF :'>l<J l-IT )t IIA~ I 31 

ri ·c: fo r sC\'Ct'fti hundn' u f et, th n expands into lt :-; hcet o l' !ant' hi(' h w:ts a urfa\' e 

flO \\' on tlw :;lop ' ol' th g rowing \'01 "lllO at the tinte the dik(• \\'<lS rorlltl'd. At th e 

lower nJ of th e dike ~o. g~ wa · eolleeted. and i\ . !J I r'prcs nts th e adjace nt 

ande itc. 

sho rt di:tam:c farther northea:t i:; an oth ' I' l.i-foot dih' . which s prca I,.; into 

a sheet ahout 500 feet ahove th ' lak ·. The tnat rial. alth u~dt :tndcsitC'. i,.; rath e r 

<.la iti · (132). It i: fu ll of :'leL:r tions (l' :1) which arc ,.; om wb~tt brt':!alti \' in their 

charact<' r. 

On the we,.;t :tl'lll of :Stee l Ba.y i. a l:J-foot dike which has :t da ·itie :tspod , 

hut pro,·ed under th e mi ro:cope to he an and site. .\.hout halfw:ty up th e rint it 

expa nd.·, L:O nnecting with th e gTeat fi o·w, ~00 f •ct thick. ext nditw from Llao H. ek 

to the northeast ·o rm r f 'tee! Ba.,·. rt till:; a. ti ·:;u re in th • mountain :; ide front 

whi<:h ~L h1l'ge part of the fi ow :c [ d. This dike. as we ll a.- mo:;t of th e others, is 

mu ·b olde r th a n the one on th e Oe,·il:; ~tckbom•. 

o d ik :; w r e,.; e n around th<' north rn and =-outh rn :-ho re of he l:tke. huL at 

the · uthcrn end of Redc loud Cliff. un de r th e oTcn.t rb_,,olitc !low of 'loud l':tp. 

thr c more dike: appea r. The one at. :-lc ntin el Ho ·k (33) i"' irn•g·ular. lO to ~-i fc t 

in width , with ·t nutu be r of.- c rctions, and for :t :-hort di:tn.nee is cut up in to a l:trg<' 

mas,.; of ·ong-lomcmtc. Farth r nort h i:- a -!:-foot dike (:H) whi <.:h strik es <l littl e 

north of ast. Tho tntnsv rsc join tinu in it is <"S [ <' iHIIy Wl II de \'l'lopt>d . It 

intcr-;C'l'ts ,.;h Pt s of hl\·a a nd c ng lom rak. hut doc,.; not r a<.:h quit to the great 

tl ow of dacitl• ah \'C. .--\.lmo:<t di rcct.ly und e r ('loud \ tp i:- nnoth<'r interrupt d 

dike, tr ' nding soutbca.'51. Althoug h th dik,.; notic·cd thus far ar o f an lcsit , 

Hn<l cadi r than the oTca,t d<tcitc fi o"·", th ir a:,.;ociati n wit h tlw portion · of th 

rint O \ ' r whil'h th ·c daC'itc flows manatee! i:- of intf'rcst. 

.\ short di:tan ·c " ·e ·t of Eag le \'e . about ha lfway between the l'1' st and tlt 

lakl. i:- n lll-foot dike with horihontal jointing. It run: t1 wn the slope to tbe 

water. :wd at one poin t stand · out Hi' a pr Hninent lcdg·t' i)() fee t in h ig ht. 

nder The \\Ta.tchman i,.; a dikl' whil'h rent hcs neith e r to th(' crest nor to th e 

w;ttcr's ~'dg·~·. It i:'i about -1:0 f et in width and it" border i:-; black and g lass_, .. lik 

tlw ,·itrophyri!' da<"itl' of Llao H9ck, but· near th e middl e it appear,.. lwlotr.n;tn.lliJW, 

with a lig ht-g-rHy <'<> lor P~ pp r d with small da rk cry:-t:-1ls of pyrox. •n c. 

HAS L'J'S. 

l 'n lik ' th~\ atHJ csites. !'It<' basalt.-; an' litui t d to tlw o~ tt l' l' : lope of :\Lount :\lazalttu. 

and do not <tppro:t ·h neare r than abo ttt a tnil p of th ere t. ;-Jon ' >f tlw 1m ·nlt fi ow:; 

l'H ill <' front tlw l'f'ntml ,·cnt of Mount :\lazanm. They a ll issu<'d from adnate l'Ones 

ttpon till' lowP r slopl':< of th:tt gT<':tt ,·ok;tno. Th e nortlwrn pa.rt of tit<' area nmpp<'d 

to nt:tins th e prinl'ip;d lntsalt ntas:;cs. whi eh issu<•d front fottr -~· ttl ,.; Titnb~ r Cmtc r. 

Dese rt 'o n\', Bald Crate r, ~tnd H.('d 'one•, 
OEULUGi" <W CHATE H KI~ \ 'l 'lUNAL l 'A I{ K. 

'l'l.ll l!lm l 'H.I 'mH B.I S t\ 1/ 1' FLQ \1". 

Ti111 be r 'ra trr .. - tnil cs no rtheast of ' m tl' r L a k , ts t hl' peak nrxt in ;.: tz ' to 

, \·ott P •ak . It rises 1., 300 feet a bo n ' t he s utTo untlitw pla in an d ha"' ~~ sont l' l ha t 

C<.;ccntri c l'O ni cal fo mt wit h u·cnth slopes ('O I'l' l' 'd htrg·•ly. to a n e levati o n of ti 7tH! 

feet, h_,. pumi ce from t he f·ina l r rupt i n of \fo un t ~l aza ma . A t li,HOO f ct :L r<•dd is h 

1·csicul a r fl ow of lmsa,l t (Ui.-) issurcl from t he sout hw •,;t ,- lo pl' . Anothe r basa lt 

strealll f o rms a pronline nt spur to the no rth w 't. The la n L is fre,.;IJ. wi t h a ll ti ll' 

pcndia ri tie:< of a re<:<' nt ftow. _\.hove t his po in t h slo pe is tn adt• of lapilli . with a 

lig ht co,·e ring o f plllni That t h ' nppl' r po rti 11 of the nto nn tai n i,.; :L einde r cOIH' 

is not scP n h_v th e mn•le r un t il he r ·1 lw>: t he s u111111i t, wh re then• is a we ll-de fi ned 

c rate r 50 feet d p an d ~50 yard.· in di:unl'tc r. T h c rat r i.· dou bl ', or mt hc r tht• rr 

ar ' t wo ·m te rs o f equal : iz sid by ·ide . O ne is n a rly no rt h of t he oth ' r. :tn d th e 

two we re most lik ly acti,·e at d itr re nt imcs. \\ it h t he prog r s>' of the r up tion 

th ' ,·cnt shifted lig htly p:tmll el w it h t h nuw c. This i,.: a cotlllllOII f aturl' in nmn_,. 

vo bwic tie lds, but is mthr r u nusu:tl in tb Cas " L l H.a ng·('. Th ' coati1 w of pu 111 ice 

f rom Moun t Mazam:L is sp r ad upo n t h ·lop e.- of he cinde r ·o ne of Titnhrr 'mt r, 

s howing that its acti,·ity h:ld clo::;rd h efor t hat of -;\Jou nt )iazanut. 

Th 1riew of rat r l Atkc a nd its rim from Ti m he r -,ritte r is CH J ·iall y tin r, and 

to t be no rt hward Mo u nt Thi el.'c n. t he ' lig ht ning- rod .. of tbr 'a::~cade H.a ng·l . . ·on1 '-

times abo caJl cu the ' · .Mat r b n 1 · of th range, ::; tands out ·o nsp i ·uou. ly. 

De:-;c rt 'onr a nd Red Cone a rc volcanoc,.; in lin with a numh •r of oth rs whit·h 

Jo rnt a <l ·icled ri dg , pmdi('ally t he c rl'st of t he ranu· . T hly arc ,,·ide nt ly d ue to 

a tnun bc r of ,·e nt.':! on o o fi:;. ur , a nd th e tnat rial eruptrd i,.; essent ia lly tbl' :<ant e 

Lit ro ug ho ut, a I t houg h th vo lcanoc · w r c not active nt th samt' ti Ill C. T h • oldest i.-

to t he no rth wa rd . and th e yo ung est is Reel Cone. At the ea .. tc m hast' of t he ridg . 

n a r t h no rth rn limi t of t he po rtio n that a pp a r;.; upon t he 111 ap, th I a.'alt is ,-t·:< ic -

ula.r (1 ' ), but fa rt he r up o n the slo1 e is ·ompa ·t Ln cl ho locry.tallin ( l !l). Thi · 

·p ur is p la inly a fl o w to t lw east. Th lant i,.; oft n ro ug h upo n t h :,; u r fa cP and 

bas lo.-t I itt! hy Wl'atb ring . pre ·ent ing· ::t.n a.' pcct o f' ncwn c. s no fo und o n t h 

a ·:<ociatcd !ants. 'l he s ummikof t he two mo.-t nort h m hill. · of t h ' ridgt· ·we rc o nc' 

c rater.-, hut the loo. ·c materirtl ha.-; I> e n s w pt away by ,.; ub:> que nt er o ·io n, cxposin ,. 

in t h ulift:-; o f t he re ·t the ·olid lan1 (l!:JO. 19 l) of whi ch th <"Cntral po rt io n of the 

cone:; is compO:;l·d . 

Des rt Co n , n ar tiH' southe rn r nd of t he ri clu·e, 11 xt to Red 'o tw. is a (' ind ' r 

·o ne wi t h ro ug· h. c·hi<'fl_,. rrdclis h, h:t:;:d t ( ! fiT). The s unnni t has a n impe rfect nate r 

hrokr n a way to ward tltP no rt h we.-t. It:< ,.: lo t)(•,; a rr ,-e r_,. stec•p . 

O f a ll the . nta ll ,-oln tno!'.- IYhi clt .ha n • furni:< lt l'd has:d t in t.h ' nor th we t<> rn part 
LA VAS 0 1<' MOU T )[AZ.AMA . ::33 

of th ar ea mapped, R d 'on i the be t xampl . lti ' well_pre ·e n · l, its htva ' ha,·e 

the fre he t look, and, all thing con ·id r d. it appear to ha1· h n acti,- late r than 

any of the crat r about the g r at central ,. nt of Mount 111azama. 

Red Co ne is campo ·ite. The ba ·a l porti on or 1 de ·tal i ' mad up 1·er · laro· ly 

of ba~a lt fl w , and th e upper 500 f t i.' a cin der cone compo.· d alma t wholly of 

lapill i,. and , a nd . laggy ch unk freeland g ray bas1LI . :Mu b of th r eddi ·h lan1 i 

v icula r, but th gray is not vesi ular. The rim on t h outh . i le i · 50 f ct abo,·e 

the bottom of th e crat r, which drain to the north east. Th rater conta in:; num rou fragments of dacitic pumice, like t ha t of th e final ruption of Mount Mazama. 

The fragment · of dacite are o abundant in th e crater and u1 on its lop as to leave 

no doubt that Red Cone had lo. eel it · Cc'1r e r b fo re th final ruption of Mount 

Mazama. Th radiating flow' which form the ba · of th con . pr ad far b yond 

th e limits of the cinde r cone. To the ea ' t th ey rn·e well xpo d, and. . me f the 

fi oii"S a r vc' icul ar. Th clongat d ca1·iti e.· ar fla ttened and li ned with hyalit . 

The gray basalt (156) i oft n ri ch in olivin . F rom th ba · of Red 'on a oT at 

h et of ba' ftlt spr ad · we tward in th flat, for e. t d country where und rlying 

ro k · a r ('One a led by a lay er of pumice. H rc a nd th er . how vcr, d mes of th 

basalt rise th rough the p umic . The fre ·h vesicular ba ·ttlt is lik that of th ha ·p of 

Red Cone f<.·om whi ch it Wfk> deri ved. I · .' urfa l' i.· well gla ciated. nnd near t he 

we ·te rn b01·dcr of the ar a 11111ppcd hr(' ll l<'i' irrro·ular a nd rugo·cd on a small :::ca l , 

with many trinted I do·cs and o ·ca ·ional Ill ·tdoll" · d tt to la1·a dams fo rme I in a 

narrow pn.rt of th n:t!l y. Rarely (1 '+) th' ha 'alt i.' platy. H ow fa r down Rogue 

Hi1•er tb · fi ow:s xt nd i.· unkn own. Ba' a lt o cu rt< alono· the Roo·u r Ri1·· r ro<tclfor 

L't1any milr: . but it i a cl;uker lant and much more vesi ular than that of R ,d 'one. 

Bald rater ha. a well-d li n d p it on the ummi t of cincl •r cone. ome 

. olid fi OII' of dnrk basalt (192. 193) a r ex-p : d, but r d and bla ·k lapi!li ar c 

m ·t ttbu ndant. It rate r, U'itw bar a nd prominent. afford ' a fin view, a nd wh ' 11 

, c n from neighb ring· 1 oin t. tand,., out co pi<:uou,.,l~· <tbo1·e the dc,p-oTe n fore:sts. 

CH .\ T E H PEA K BA SALT F I,O I\'. 

'mter Pe<tk j,., tb . (" nte r of a . mall n.rea. of bas;tlt on th divid extending 

Routh from ' a. tle 'r stand \ idac 1 a k hdw n una. and 'ttn creek . The hill 

rises ov r 700 f <'t aho1· tb g· neral level of th e platform of a nde ·ite on ll"hi eh 

it r e ts. At the north ern ha ·c of tbc hill i a ma : of r ddi ·b-l>ro,vn bas<dti c tuff. 

Th g·en ral lay er of pumi ' extend: fa r up t·h ' . lope, ;:bowing tha.t, a· in othot 

ase:s, ' rater P ea k wa .. not a tivc nftcr th<' fin al outburst f rom Moun t Maznma. 

Tb pumi ce htyc r i · d 'c i !ed ly darl· r than tb material of which tb · peak 

9255- o. 3- 02--3 
34 GEOLOGY 0.1!' R 1'ER LAKE NA1'IO AL PARK. 

(179- 181) 1. compo ed. Th ·one is ln.rgely if not wholly fragm ntal and .ther e 

is no defi ni te l:l ow from it un l, · it xtoud to th e northwe:st. mong th prevailing dark fragm nt of ba ·alt thor ar c o ca. ional and itie fragment:' hurl d 

out from the nnd rlying and . it ~< . Th . summi t f Crate r P ak ~ a " 11 -d fin ed 

crater 100 yard · in diamet r and .£15 feet de p, d rainirw to th :;outhw st. ' ome 

good- ized fir g row on it, and it ontains a bank of snow a.· late- a. ug u t. 

Ol'HE lt l•' LOW •. 

Toward the southwe tern corne r of th pu.rk th r i a laro·c }11' a of ba alt, in 

which ther e is con iderrtbl va.riation and th e ma. s nmy ha,-c b en built up from a . . number of ,·ents. It forms a blu ff ncar th<' roa.d !'outhw :-; t of ~nllfL re k from 

Pole Bridge Creek toward tho ummit. lt ran o·eR in olo r from gray and l·eddi h 

to almo t black and som i ' 'e icular. North of nion Peak it rise.· to over 7,000 

feet and i a o ~tt d with ba altic tuff. Th di' ide ftt thi point i a ridge of 

ba altic lap illi , indicatino· th proximity of a volcan ic ' ent alth ougb,no well-defin ed 

crater wa : een. The ro ks are well ula ·iated and th origina.l form of th cind r 

con may hav e been gTeatl,v modified thereby . Th ddo·c of lapilli a.ft'ord a fi n 

view of Uni on Peak a few mile far ther ·outh on th cr t of the ranKe· nion 

Peak i rugged and cornpo. ed larg lj of and ' ite ' hich came fr m a v nt which 

was more ancient than that frorr which th ba. n. ~ i, u d. p n th north rn 

border, a. els wher e. oTay (16+) and rcddi ·b (1G6) · lors ar ·omuwn, hut 

whole th e darker colors (1 :u, l 7, 163) ar mo t abundltn t, and in pla e . 

near the Rogue Rive r road, th ro k i decid dly platy . 

n t;bc 

p eiall y 

In the outhea. tern c.orner of th park j -· a hill of ~< ·o ri a · ou. ba ·alt with l}lpilli 

overlying dacite, and ' e t of thi. , in the flatter country near th e bord r of th park, 

th ere are bowlder · and bluff. cau ed hy str amr; of basalt which may ha,·o d s end d 

from Crater Lak , althouo·h the conn c tion wa.· n t ob.'er vcd. Th fall.· of Anna 

Creek below the fork ar over hasa,lt l ut th xpo ur e i · very :-~ mall. mall ar a · 

of ba alt occur along the road between the fa ll · and _Pol Bridg re k and ba alt 

may cover much of the ountry marked ande ito in the outhwe>;te rn portion of tb 

park. 

DACITE . 

\ 

Dacite ar e much les. abundant t han mde ites in the rim of 'rater Lak , but 

unlike th e ba alts, they come from th . am g n ral vent. Th y are v ry un qua lly 

distributed. One fl ow is on t he . outb rn . lope ·omc eli tao· from th e. ummit; tho 

other · ar e along th e northern ere. t of th rim an l a r later than h andc ito·, 

exc pting only the andesite of Wizard I land. The >eparate flow · to b con idered 

a re those of Sun Creek, Cloud Cap, Grou. e Hill , Llao Rock, Wincgla s and 'lc twood Cove. Among th em there is wide va riation, from ob idian throug-h phcrulitic 
LA\ A OF MOU 1' MAZAMA. 35 

to we ll-banded and largely cry tallin material, wh ile orne are mud flo w str aked 

with black g la . 

. 'N CHEEK DACITE FLOIY. 

The canyon of un Creek below the fa lls ha · upon th w st a num ber of Jifi' 

and terrae , due to ·uc es ive flow of dacite xpo ing- a tota l thickn ~ f al ut G 0 

feet. At 6,300 feet ea t of Crater P eak th ·liff · hegin . The £r ·t i 200 feet mad 

by a . oli d flow of dacite with con picuon · truetural feature . The next te rra , at 

~ 9 0 fe t, :A'})O a d cided ly perliti c and , ph rnliti rhyolit bandrd with mall 

lithophrre. and form a bluff 75 fe t in height. Th ere ar han l of pe rliti a nd 

·pberuliti · grai n: alternating with others 'vhi h show n ither tructur . t 5 7 0 

feet i a plain of £nc materi al filling the \

7 all ey to a width of tbr -f urtb of a mil . 

In th e oft materia l un reek ba. uta canyon 200 feet deep. Upon th a. tern 

: ide in the canyon wa ll dacitic rock · (123, 124) appea r, onta ining cavitie lin ed itb 

minute cr y tal ' of tridymit . Tb layer of pumice 'O\' ers n arly ,. ryth ino· b yond 

the a11yon o that the nature of tb un derly ing rock i · toft n. id rabl xt nt a 

matter of doubt. On the v\ e ·t Fork of un Creel ju. t abO\·e wh r e it b g ins to 

cut a canyon in the material filling th Ya ll y , ma ' e.· of da ite (125 126) app ar, and 

if not in place bav not be n moYed far, fo r the rock.· immediately to the north ar 

a ndesite. On the 'Put' b tw en the 1\ est Fork and tb ma in , tream f and re k a 

w ll-marked dacite (127) occur ' with con picuous fluidal banding aud alig ned ca,·iti 

padding with tridymite· it apr ear·· to form th whol ri dge exc pting th e , ma ll 

capping of andc. ite. hort d i tan c farther north a strong pring i ·su from 

the contact betw n tb da it and the overly ing Rnde. ite. 

Th ' un 'r It da it i th olde t about rater Lak It i e\·idently older 

than the and ·ite which li upon it at an altitude of 6,600 fe t. Thi on-

·id rably above the lev I of the lak , a nd if the rhyolite arne from Mount bzama 

it ;:; hou ld app ar on tllC inn r lop of t h rim under Dutton li ft'. F r m a boat 

by th ·bore the cliff wa xamined to ec if the da ite tlow could be r ecognized, 

but it wa not fo und. 

'LO D ('AP DACITE L0 \1'. 

loud ap i::-: on the eastern re ' t of the rim and_ marks the point of departure 

of a ~tr am f dacite which ·prcad to th e o01·thea t. It forms a larg part of Redloud tiff whi h take. it: name from the r ddish-yellow tuff or tuffaceou · dacite 

that underlie tb principal flow. Thi flow or, rather, group of flow - for it appear 

to b mad up of at least thr e tream - form a prominent cliff forO \ er half a 

mile along the rim and ha a thi knes of ov r 300 feet. It appear to form onethird of the inn r lope of th e er e t. This flow pr ent a erie of oTeat cliff 

fLbout i bord r ·, e p cially on the north we 't. Th fin e t i upon th we. t ~ide 

nearly half a mile from the Jake. It i. 250 feet high and of g r eat length, ·mootb 
36 GEOJ,OGY OF CRATER LAKE ATIONAL PARK. 

and poli:shed a if by g lacier hut di tinct 'trim co uld not bC' found. The rock 

(11 ) is e:specially glassy, often banded with brown, and m11y b fine ly ph ruliti c 

or lithophy al. Th canyon beading betwe n , loud Cap n,nd ott P eak: pre e nt.'l 

cliffs which are le,s impo in g. pon the •a t side of tbi.· ~tnyou at the northern 

end of the flow the ro ·k, although da. it , i · more ma . ivc a nd Ia k tb vitreous 

featur of the main body of the flow n ar its our . To the w t thi · . eric · 

of dacite flow a.Jong th sout hern ann of r otto ,0\' , ntay b seen to ov rli 

the adjacent str eam of andesite. The bas of tb cia ito flow near the ontaet i 

gla · ·y, with numerous ·pherulites and li tbophy. re. 

Farther northea t, between th e forks of Bear r eek, i.· a . m~tll area of dacite, 

which wa r egarded as an ande ite in th fi ld , but Dr. Patton tinall.v r legated it to 

the dacite . The regularit) of the hill o-av ri to th xpecta.tion that it would be 

fo und to b a cinde r ('One but thi i not the ca e, as it i · ·ompo ed of . olid da itic 

Ja ,·a. Its ide are over d \Vith Japilli of pumic Li ke tb,tt found I wher e and 

upon the south bear a fine gTowtb of yellow pine. Th re ar fl numb r of oth r 

bill · farther north which appear to be compo d of the aru mat rial. 

HO US~: HILl, DA l'b~ FIAlW. 

Po. ibly of about the am relati,·e ag-e i the G rou · Hill fl o, , which cro · 'C's 

the ere 't a. short di. tance nortbea:t of L la H.ock. On the inn ' r , lope the la.y r 

of pumi ce b neath the great tlow of Llao Ro ·k o\·erlap ' the Grou. e Hill flow, !towing that the G rou ·e Hill flow i ·old ,. than th Lhw Ro k ruption. For tbi · r a · 11 

th e two flow . ftre eparatcd on the map. At t he ooutb ba e of I'Ollil Hill tb 

dacite (10'7) i regularly banded, and on the hill n xt no rtben t of Llao Rock it (LO ) 

is pherulitic. Thi flow ha beP n much e roded, and ba a mor a ncien I k thnn 

other flows of this portion of th rim. 

Lt. O 'ROCK DACITE FLOW. 

The Llao Rock flow i one of the mo:t intere:ting- of th' region and i.- th 111 . t 

conspicuou ·. Its gener al outline in crO.'$ ·ection fi lli ng a ,-all y of th rim m<t,\' be 

clearly f'e n (Pl. IX, '.I.) aero. the lake. The flow i~ m r than a mil e wide a lotw b 

t he -rest and over 1,200 feet thick in the middle tap ring to dge on both ~;ide:. 

Con ·idering· it.- great tbickne ·s the fl ow i · remarkab ly short, fo r it c.'tn 1 trae d 

with certain tJ only about a mile from the rim, although it may xt nd for HOI11C' 

di~tan cc fa rther b neath the pumice· over d plain. On th nortbea. t it tnpor:-< 

rapidly to an edg , and ends in a mas of pum ice nearly 100 feet thick. The lower 

portion of thi pumice i:s clea rly t ratified, but i11 the uppe r part the li ne.- a r 1 .-

distinct. The valley fil led by the fl ow i.- ·mall and ha.- an irr g-ular F< urfacc. n 

the northeast ide there is a promin nt ma s of pumice CPl. IX 1), unde r th e 

Llao Rock flow, b ut on the oppo:ite side th r e i. li ttle or no pumice. 011 tb 
1..1. S. GEOLOGICAL SURV£Y P~OFESSIONAL PAPEA NO. S PL. IX 

A . LLAO ROCK. 

11. FLOW OF TUFFACEOUS DACITE EAST OF PUMICE POINT. 

IJ A VAS 0 1!' MO 'I' MAZAM A. 37 

summit of Llao Rock th r i rnuc·b pnmi c . On th we tern ' lop it ba::. h n 

larg ly w pt away , expo ing th und rly ing r ck. Th edo·c of th fl ow, aud, 

iu fa t, the ntire periphery , i practi a.lly obsidian; th interior portion i more 

cry talline. Whe re gia' .r it i · ri h in :;mall f ld,.;pars (102). On the ummit, 

whi ·h bas suff r rl much from E'rosion, a p orti on of th . fl o w (103) ori ·inn,lly onw 

di tan(' • benea.th th surface i xpo ·cd , and on thi.· neconnt the rock i:-; n th 

whole le ·:,; g la' . y th<tn n n,r the horder. 

An imp rfect columnar ,;tnt ·tur i::; given to tb da it.e of LhlO Ro k by two. t' t :-; 

of join ' . Ones t i · radin,l from tllf' lake and perpendi ular to th(' rim ; th othC' r 

et cro e the :f:ir: t nearly a.t right ang l s. They n,re be ·t de,· loped in the low r 

portion of tb fl ow. N ar th ' urfa ·e a cutT d tru ture due to fl owing i · marked. 

Below, the flow ·tructur is . trai o·bt and n('arly hori:r.ontnl. 

WI NEGLA S D.\ CITE FLOW . 

The Winegla · · f:low i of small ·ize and 1 eculiar. It Ji in th next gap of tb 

rim sou beast of H.ound Top (Pl. VII B ). ha a width of ·arc lj ~00 fe t a I ngth 

of probably a mil , a nd a thickn f about 20 f t. It i rl cid edly lik a tuff (1 H ) 

and mig ht well b • so con ider .rl were it not fo r the tring ~ of bla k O']fl. s int rming led with n, r eddi: h undma s co nta ining frao·m nt of oth r mat rinl and 

imparting a d cided fluidal tru ture to th ma ·. 

hort eli ·tan c fa rth r ca ' t ther e i an th r . mall be t of thi ' tuffaceou 

dacit 10 f t thi •k. It ha th characterdic streak of black o·la ' which lix it' 

iden ity. It oc ut" locally along th w t rn edge of the ' loud Cap fiow, and 

clo ly r robl : mu h of the tuf:faceou material of Redcloud lift'. At the 

Win gla .,, ,'lid it is imm diat l_y a sociat d with puroi • ous tulf. The hard rock 

of th rim i · an dc ite. ,. rlain by 15 f et of pumi c ou · tuff with 10 fe t of r d 

tufl'n ou da cite. Tbi,.; i.- \1 rlain by 30 f et of conglomerate and capped by a :fine 

lay r of pumi C' 25 fe t t hick. It i • E' vident from thi · , tion that the fragmental 

dacit do not r pr e nt th e final l'tlption. for tha. finds expr :s ion in the top 

Ia.) er of pumice. 

Th ~tp w ·t of Round Top coota.in · a ·mall ·he t of tuffaceous du ite lik that 

on tb othC'r id , but j thi k r. It appear in P l. Vll B at th I ft of the Palisad 

rown d by Round Top. lt i 50 fe t thi k in tb middl and taper to a thin edge 

on the w t. On tb a t of Round Top it extend up the op a hort di tance, 

for it i cl arly een abo\ glacitLl strire and i undoubtedly a p st-Gla ial flow. In 

tbi gap, a upon tbe ea-t, it overlie a sh t of pumice and underlie conglomerate 

into which it appear to pa by becoming mor fragm ntal. ear the w tern 

edg of the o-ap it app ars to b overlain by larg b wider ·, and wh er the exposure 

of the dacite cease the sheet of large bowlder b comes mor marked. On the 
38 GEOI,OGY OF RATER LAKE r ATIOr AL PARK. 

g-eological map thi area of dacit adjoin the edg of th uT at flow of Rugged 

Cre t. Tn r ali ty, h wever, it overl ap th Ruo·g d 're t flo\ and i of later date. 

The . ame tuft'accou · da ite c urs farth r w ,-t along th ere. t heyond 

Cle twood 'o,·e wh er a upon th a. t, it O\' rlap::: th fl ow of Rugged 're. t. 

It extend n arl.) to Pumic Poi nt (Pl. lX, B) wh re it n.pp rn· · betw en two thi k 

ma. es of pumice. Tbi p culim· tuffac ou da it o curring a lorw much of th 

northern cr st of th rim all b long: to on flow, whi ·h p1· ad as a un iformlv thin 

·he t ov r that portion f th ba c of 1ount Mazama. lt i. nltoo· tber unlik th 

other flow · of da ·ito and appears t b int rm :lint b tw n tb m and tufl. 

CL}: ET\1'0 D COO: J)A ITE l•'L0\1'. 

Among th final flow of th g reat vol ano is tb rH' f I twood Cove. The 

rim at tbi point i. remarkable. It i unlike any oth r portion of tb rim in i 

rugged rough ne s without l eing harp edged lik a tl re t. It i. wooded with 

mall pines and :fir , but th bold crag . tand out a.mono- th m in pinnacl ed r elief. 

The lava is a black, . ellow, or brown gla and i · gr atly broken a.nd rough on the 

top. It form th cr t of th rim f r nearly a mil , xt nding upon both ide of 

leetwood ov wber it mak promin nt !iff . It Jill' an old valley at th h ad 

of the ·ove, and ba a thicknc' f over 300 fe t in th , mi ~dl ', tap ring· to a thin 

dge on hotb id . Pl. X, B, illustrate· it app arance from th e lak . Thi ' I r ad 

tiow extend· from the rim north astward for nearly 3 mil wber it di app ars 

b neath th plain of pumice and gla ia 1 material. The hottom of and ite on whi b 

the da ite r e i. in gular, and in place th two rock · ar ,epara d by a thi ·k 

layer of pumice. 

On tracing the rugged rna . of dacite away from the lake ther i. found upon i · 

urface a . mall valley (Pl. X, A) lined with li £1'. and local olumn . Tb' \' Hll y i 

nearly a' d ep a · wide. Huge blo ·ks of dacite have tumbled ab ut in the mo t 

irr gular manner producing mall in lo ·ed ba in . Th Ya.ll e. i not a wat rwny, 

and judging from it peculiaritie it i a! tog ther probable that it i. a cav d-in ]n,, n, 

tunnel. 

pou both . ide of tb urfaee th dacite i flatti h and lookR gin iat d, } t no 

certain gladal marks could be found, although lar o·e fragm nt · r gard d a · bowld rs 

were een re ting upon it. We. t of the chaotic channel and al. o on th ea tal ove 

the clifl' ther appears to be some mora ir~ic mat rial. Clo to the cr t ;~. t the head 

of leetwood Cove the : urface is mo t broken and r ugged. little farth r we t tho 

flow thin rapidly, forming W t Deer Cliff, and run:' out n ar the n xt point. 

The upper portion of the . ide· of Cleetwood Cove· ~ a cliff of dacite, b neath 

which ther 1 a layer of pumice, succeeded downward by 350 or more feet of xp d 

andesitic flows. These subdacite lavas are conti nuous around the head of the cove, but 
A . VALL EY OF CAV E D-IN TUNNEL 

l :J. CLEETW OOD COV E F LOW. 

LAVA OF MO T MAZAMA. 39 

ar e not expo ed. the bead of be em tb y ar o,- r d by dacite ' hi h flow d 

down the inner . lop of the rim from t b a ' 'ed-in tunn 1 of Rugged ' r t to he lake. 

The How i. wid above and narrow below lapping down over the edges of thP 

and ite into th lake. How far it extend s h n ath th e snrfac·e of th Jnk is 

unknown hut appare ntly onl.v a .. hort d i tan e. 

ome eli tan above the lake, upon hoth ide th ilow and platy tru tu r of 

th e dacite overlying a nde ite d ip toward th e entra l tr am, wh i ·h in plac dip 

toward the la ke at an ano·le of 35° and li parall I to th pre ent ur:face. 'fhe 

tructure in clined toward th Jake i. cry clear and it para ll li m to the urface 

underneath well xpo cd upon both 'des. 1ear the summit the gla , y rock (111) 

i r ed and black , and may be mixed with g ray. Nearl. midway from ummit to 

lak , where the lope is teepe. t, the lam (112) i · om at l ~ g la y than n ar the 

er e t, and near h lake (11 ) the ry. tallin . tru tur i till mor m:uked. 

DACI'I'I DIKES • . Only two of th elev n dike· of Mount !fa~ama ar dac it . Th y ut the older 

ande ite (57) and ·onne t dire tly with th e thi ke t part of th Llao Rock How. 

On of the dik . has t th ickn e . of 10 feet. In the middle (13 ) it is ho1ocry talline 

and contain ry tal of hornblend , but upon tb border it i · bl11 ck and glas. , a 

vitropby re (131), like most of Llao Rock. The other dik i r g ular, vary ing from 

2t to ± f t, and th materia l clo ely re mble the la tin allre pe ts. One of the e, 

or po ibly b th , ontri bu d to th e cape of th gr eat ma of Llao Rock . 

.OA !TIC' I' Ml E. 

Th daeiti eruption · of Moun t Mazama were generally accompani d by more 

or l pumice . Pl. IX, 1 how. ·a la rg amount of pumice which underlie th e 

L la H.o kdacit and hichis,th refore, om whatoldertbanthat tlow . I ti·arranged 

in In,y l", probabl) uue to th a · ·orting influ nee of the atmo ' pherc. ndcr the 

main body f th fl ow the ' beet of pumi ·e i. , m time· tin~Y or thin and 

itT gular. It i.- po. sibl ,that thi- 1 umi ce b lono·s to the ea rlier part of the 

ruption which gave ri.-e to Lla Rock. 

The ummit of Ll ao Rock i · ompo ed of fragm ntnl material, approximately 

120 f et in thi knc , of which the lower 90 f et is pumice r ting on the 

urfa e of the dacite. It i l' lear that tbi bod. of pumice is htt r thnn the L lao 

Roek flo' , although it may b long to the final porti on of th .-ame eruption. The 

lay r of white, piuki b, or y llowi ·b pumic of th rdinary dacitic type (136) 

on the . ummit of Llao Rock i v rlain by 20 feet of more or le p umiceou 

mate rial, whi h i heavier and much darker in olor. The f ragment , like tho e 

of tb lay r below, a re mall, bein~Y mr ly a larg-e a 6 inche in diamete r. 

Some of them (143) ar e black, rich in phenocrysts o:l' homblende a nd f eld par, 
40 GEOLOGY OF RATER T,AKF. A1'10 AL !'ARK. 

and ar doubtfully of a dacitic natur : Tb r an h n q u tion that the darker 

lay r r epr e ut · tbe conclud in · tag· of th final xplo.·ive ruption of Mount 

Mazama. It i · one of the la rg t mu . · of this :-;o rt f mat ri a l found anywhere 

about the rim ere t, and i::; of unu ·ual im1 ortance on <LCC' unt of its peculiftriti , 

for it i markedly unlik e any of the daciti e la va . 

Alono· thr er ::;t RbO\'C Darw r Bay, ncar ' ntine l Hock th re is a ·u ce ion 0 0 

of pumice and g lacial deposi . Th rr ar two d p ·it:; of ' bat; app at' to b 

glacial gra,· I::; :-o ucc cded hy lRy ' r·· of v ry pumi ceous ma.t ri ctl, r rdirw the fact 

of alte rnating g laciation a nd v I anic eruption . Th lfL[ illi of the two pumi e 

layer appear to b t h same. Farthe r to th northw t, beyond loud ap, a 

thin be t of tuffaceou · dacit app ftl' at the top of th low r pumic . 

Tuff with much pumi ceou fraO"tn ntal mat rial i::; wid ·pr ad in tb ' rater 

Lak region, and is ·o ftb undant in place · a to indicat a g reat xplo -ive e ruption 

among the finR I en >n in the hi to ry of 1\lount Mazama. Pnmic D · rt i · a 

treeles. tra ct north of the rim in wbi h j)Umi ·c p r ,·ails. F ragm nts ar u. ually 

from 1 to+. inches hr uo·b, although om n a rly a foot in diarn t r are ommon 

in places, and occasionally larg r on s app ar. Th larg :t rna · of dacite n 

(13 ) i · 10 feet in d iameter. It i ve ry pumic u · and ·e t di tin tly fragm n!k1.l. 

ear by wao:; a, fragm n t 3 f eet in diam t r, rich in bornbl nd . u h frao·ment.~ 

are 11 0 al>ulldtLnt, a lt!H ugh black and (1 .J.) compm;C'd chi fiy of f ld ·par a.nd 

horn hi ndc i' a.bundant everywh r e. H er and tb r may h e n c a -ional 

hunk of a.nde. ite. From Mount Thi l··en to Red on , a d i tance of O\'er 1 

mil e·, nothirw but fragmental material wa ' "' n ncar hr trail. R l 

approached som of the red and black lapilli wa bed from the ·on apr ar upon 

the urface to oYerlie th e dacitic pumice and t nd to o-iv a \vrono· impr ~ i n as t 

th ir order of ruption. The. h et of pumic . although not indicated upon thP mftp 

co,·er: by far th e larger part of the flow , but ledge. a.r in g ne ral Kuffi i ntly 

numerous to dete rmin apr roximat ly tb d i:tri hntion of t he variou · I ind of 

lava. Along the :outhern bord r of tb rim th gr at t th i kn . ·: of pumice 

about lO f e t, i: ex po· d ~Lt th top of Dutton '!iff. Th hu·g ._t fragmc nl:i' at that 

place a re not mor e than a few inch in d iameter a nd app ar to bo th e fa rtb 1't from 

th rrru. The peculiar hlack lapJlli ri h ro c ry ·tal of hornbl nde arc num rou . 

pe 1men 1:1:2 was coli cted from a pi ce 1 inche: in d iameter. lear th am 

place, 1n 1 ' 3, I fou nd a bowld r-like homb of the am ·ize a thflt not d abov . 

It bad a blackened . hell whJCh wa: crack d to a little depth, a nd the era k stood 

op n llke those of a b ur ·ted apple. ThP, ou ·id wa · very hard and g li tened (14 ) 

as 1£ m lted and glazed. W1thin tb rock was very porous a.nd pumic ou (147). 

ear by another pecimcn bad a thin, reddi b, cracked rind with a mor cry talline 

g ranitic center. Specunens 150 a nd 151 al o were fou nd along the northe.rn rim 

of the lake and belong to this peculiar ej ctameuta. 
GLAOIA'fiON OF MO NT MAZAMA. 

On the broad di' ide north of Crat r P eak i a ur ornin c ompo cd laro· ly f 

and e ·iti material. Jt i · cover ed with daciti · pumiC' in such a way a to mark th 

r elati,·e age of the g laciati on and ruption. 

GLACIATION OF MOUNT MAZAMA. 

The glacier · of Mount l\la ~anm bav I ft listin t r co rd. · in th - fo rm of tri ~ 

and moraine ' , with their OUt\Ya ·h plain . lo,·vcr dow n upon tb mountain lop n . The 

radial arrarw m nt of the -t ri a~ a ro ·.· the v ry cr t of tb rim overl okino· tb lak 

is cl arly eli ·played, a: bow n on the map (J>l. VI). The rock arc w 11 triated, 

e p cially upon th e we tern and ·outb c ro Te::> t, and the o-)a ·ia l utting ha be n 

·uffi ci ntly d ep to r move all th ·urface features of the lava. flow on the outer 

lope of th e riru. On the adjacent slope toward tb lake the same roclc pre nt 

roug h fracture ..; urfac s ··bowing no triro. Th glaciation of th e rim is a f atu re of 

the outer lope nly , b ut it rea ·be. th '' ery r nt. The a-lacier ' bat . triat d tb 

crown of th rim cnrried ' ton ·. in their low r part ·, and munt have com down f rom 

above. The c ntral p ak from whi ch he glaciers ra liat d bn di appear d, a it i 

evid nt that the topographi c ('Ond ition of to-dny a frord no ·u h our e of upply . 

Th orily portion of tb rim along which positive : io-n of g laciation w r not 

ob erved i oppo ite ott P ak, a nd yet it i altogether prohabl that g lacier 

xi ted h r , for near ntinel Rock there appear to b two Jayer n of g-ravel of 

g la ia l orig-in and th re arc ,·id0nee of o-laciation in tb Yall y beading between 

loud ap and co t P ea k and draining thif:' I ortion of the er e t. B low the 

ca ·cad • n th outb Fork f Bear Cr e k th.c mil y i · border d -by one of the fine t 

laternl m rain of the r g ion. It 1 · practi ally ertain th refore, that th cr e::;t of 

tb rim ha be n_ ,,;laciat d throughout it entir circuit, exc pting po ibly Gla ier 

P ~tk and th two hio-he-·t p in in the outbern rim and y t alono- th e e portion 

of the r im tb re i ' the clcar e t videnc of d p g lacial cutting-. 

On th low r lope of Mount 1azama, tl:ie g laci r >v rc broken up into 

tongu . of g lacial icc whi ·h o cupi d the valley,; only following losely the line of 

drainag . One of tb large, t of the ma o cupi ed tb Yallcy of Anna r ek 

in th bottom of wbi ·h o·lacial triro ha\ c be n found at a distance of over 3 

Jl1il from the lake. B y ond th i point all the hwa fl o, in tb midd l portion 

of the vallf\y ar on ·eal d by a thick coatino- of fin e Yolcanic d tritu wa hod 

down from the highe r lop of th e volcano, fillirw the vall ) · to gr at d pth. 

and ffectually ob, curing th r cord mad by the rrlacier nt the time of its 

greatest exten iou. 

The morain of the Anna r ek glacier on the rim near Victor Rock ha a 

thickn · of over a hundred f et. It i comi o cd of ttngular frao·ment up to 

feet in diarneter, commingled with and and day. Near by, on th outer lope, at 
42 GEOLOGY OF RATER J,AKE A'l'lO AL .PARK. 

th head of th main di,·id tw n nnn and a tle cr k ·, it bowlder 

covered. 

On d cending from th r t to th o ·prings nt th bend of una Creek, 

terrace may b cen bord rino· a , harp V-·baped canyon cut wholly in morainal 

mat rial containing . mootb d bowld rs of nnd ·it . Some f th m are lark. 

colored and inclo, O'l'aJ' ecr tion ·. Th U-·hap d aci~tl vall y f \nna ', ek, 

a bort di tance b low the cre' t, i. 120 f t d ep with morain e ' on the id and 

on an irreo·ular bottom 50 yard in width. Tho cany n head · again ·t cliff over e • 

which v ral ·tream ca cad , to di ·appear in th debri b low. Th y ar fed by 

the now bank n ar the r ' t, i.n which the Anna 'r k g in ·i r ba' not mad a 

decid d notch, a have the gla i 1\ of un and and er k . 

The moraine-filled vaU j of Anna Cr k, 1t mil e-.: from th lak bas a width 

of n arly half a mil wher m adow b gin. Tb m ad w. b coLD wampy in places 

with fine pa -ture on omewhat irr gular bottom and continu to a morainal ridge 

20 or 30 feet in height cro. ing the valley diagonally to tb outhwe t, where th 

principal stream break through. At thi t rminal morain th wampy pat<:he ea e 

and the valley b come broad a.nd dr . Tho tr am near th w t . ide, after pa in()' 

the momine, oon begin · to cut into the som what irr gular nrfac , wh r it be orne 

a well-marked plain cover c1 with pumi and tudd d with pin · ad fir: of moderate 

size. 1 he . tream ·ut de p r and deeper into th ,plain a it adYan s r ,- al ing n 

ma of fragmental material without definite ·tratili ation although in pla th r 

ar line parallel to th , urfac of the pumice-cover d plaio . Thr e mil . from th 

ere t, and at 1 a t a mile b yo nd the ·mall terminal rn orain noted abO\' , the tream 

expo es the rocky floor of the va ll y, which i' cl arly g laciat d. T he main tr am at 

its junction with th we t fork. wh ich fl ow: from th larD' : pring ncar the wagon 

road i a caoyoo 300 feet d pin compnrati,- ly fine vol · nic mat rial , like hat of 

the plain above. The wagon road down the right bank of nna r k f llows th 

plain for mile and afford fin view of th canyon. t th mouth of Pol Brid 

Creek the plain i hummo k . It ha. not h en level d off and. apJ ar to b 

moramal, perhap a portion of an arli r terminal morain of the nna 're kglaci r 

or of a .-ide glacier along Pol Bridge Cr k from nion P ak. Thi mall vall y i 

full of morainal material from th ni.on P ak region, whi h wa al o a gla ·ial c nt r, 

a · is hown by the trire near th outhwe t corner of th park. Th : tri· vid ntly 

record au ice mo,·ement from the nion P ak region north and northw st to join 

the Rogue Riv r glacier from Mount Mazama. Th di ·tribution f thC' mora111al 

material ugge ts another branch down Pole Bridge Cr k to th Anna reek glacier. 

The canyon of Anna Creek above the mouth of Pole Bridge Creek i bown in Pl. 

HI, B. Below that point it ha a depth of 300 to 400 fe t, With almo t inacc s ible 

wall frequently ornamented by column and other carved form compo ed wholly 
lJ . 8. GEOLOGICAL SURV£-.' PROFESSIONAL PAPER NO. 3 PL. XI 

JOINTED TUFF OF ANNA CREEK. 

LA IA'l'IO 01!' M T MAZAMA. 43 

of vol anic material. There arc but f w pla e. wher th ' tr am ra n h r Rch d. 

It i · compl et ly box d in l y clifl.'s, in which the joi nted , tru tur (Pl. X I) of the 

lllaterial i:-; prominent. 

The ice at tbc mouth of Pol Bridg Creek may hav l ecn not l .·,.; than a 

thou.·and feet thick, for it poli bed the rocks at an IC' ,·ation of 6,500 fp ton tb 

·ummit imm diat ly :outb of that ·tr am. The terminal morai ne f tb Anna 

r eek g laci r at tb tim of itP oTeate t xten ion may hav be n buried by tb 

deposits of th e Wood River alley or th Klamath lake . . 

The g lacial ph nomena of Anna 'r ek illustrat qu it fu lly tho ' c of all the 

othe1· important tr am beading in ·1\lonnt Mazama and may b tak n fl' a t:p . 

In gen ra.l, the moraine. of the upper slop . arc ·uc eed d by xten ive plain of 

.-and ttnd pumice which fill the Yall y.- t gr at d pth ' and g iv ri, e to tb box 

eanyon in which the r·tream leave th low r slope . of that g reat ,. lcano. 

Anna r ek earrie a larg r proportion of wate1· from the rim of 'rat r Lake 

than rlny oth r tream, for th rea on, mo t li kely, thflt it r ecciv much of i 

.·upply from the oT at nowdrif · aught within the outhw . t p rtion of tb rim 

ere t. Ea t of it lie un and and cr ks, b tb of wb i h ccupy w 11 -mark >d 

glacial Cflnyon . In strono· co ntra ·t to th e are th ...-a lleys of 'a' tl ' re k and 

other tream · whi ·h ]rain th w ter n lop of Mount 1azama into Rogu Riv r 

withou p rc ptibly notcbino· that p rtion of the rim unle - we eon id r th gap 

I t\v en Gla ial P ak and Llao R k a. such. Th bo\Tld ry moraine urfac on 

th Rogu River sid of th rim i. be t di played at the .head of Ca tle Creek. 

lonD" tb roa l to tb lake and b low it ar gr at plain of and and pumke 

. tr tching f r wany mile. doYvn Rogue River. Ground morain i wide ·pread, 

but no on ·pieuou terminal m rain wa noted anywber on th we tern lope. 

Po ibly it ha b n cov red up or may have been incon ·pi ·uou · and overlooked. 

'\.. large glacial tr am til led th broad valley b tween Glacier Peak and Llao 

Rock and pr ad ove r tb broa.d plain w t of Red 'one to th e western border of 

tb park wb rP a remarlmbl ,.:c ries of meadow·· o uJ", due, mot likely . to glacial 

dam at their I w r ends. Tb Rob·nc RiYcr o·la i r ha i a width mea ured alone; the 

ere. t of over ± mile, and wa ' pr bably by fn r the large t o·lacicr of Mount Mazama. 

Th can on f and ~t nd ' un cr ck ' are among th mo t ·triking glacial 

1 h norn 1 a of Mount Mazama. Th notch · tb · y make in the rim ar promin nt 

:.' atm . . The canyon ' ar ]early f th gla inl form. Th ir wall ar ·laciated and 

th ir ftoor · ·trewn with morainal d po i , which on and Cr ck ar ucc d db low 

b) the u ual box canyon cut in tb plain und rlain by thi k depo its of volcanic 

material. Tb canyon i not so d ep as that of Anna reek, and the de c nt to tb 

plain of Klamath Mar h at th a t foot of tb mountain, i gradual. In the ca e of 

un Creek the condition are omewhat difi' rent. For 2 mile from the crest the 
GEOL GY OF RATER L KE A'l'f AL PARK. 

g-md i g ntl ' and the broad v n floor i · on ght irtl dobri. ; th n the cr ek d nds 

abruptly, by fall. hundred · of f t in h igb , t rt relative] narr ' ·anyon, which 

~Lttai s a depth of over a tbou:;and fo t, and onti nucs to th plain of the Klamath 

lak ·. The canyon wall · arc comp c l of la it t rrft od b ' sue e siv flow much 

older than the gorg . The canyon, whi ch i ' the g r •at on O}JI ite Crater P ak, h~ 

a floor of fine mat rial tin e-fourth ' of a mil <' wide, in which tb pre cnt tream ha 

cut an inner ca nyon 2 0 f et in d pth. Tbi · . any n may differ from that of Anna 

and and creek' in the am un t of filling bnt w ha,· no full m a ur of their depth. 

On the other band it i · ~ ibl that tbi d pro ·ky canyon r cord. a condition not 

found el·ewber about rater Lake. 

Th cuttino· of tb canyon of un and Sand cr ek,· wa · the final glacial work 

of 1ount Mazama. The are tb on ly ones c 'ming down from the upper portion 

of the mountain and mu t r pr nt its prin ·ipal str 'am '. They would, ther fore 

co ntain the gla ·ier:5 wh i b r main d aft r th po h of g neral glaciation during 

which the broad divid hetween th·e canyon.· w r ic cov r d. 

The nortbea t lop of th rim ~ a w ll a la ~tt d b. 1na · d c nding into the 

forks of Bear re k, ·p ·ially th ou h Fork, w h r tb morni n fi eld i' larg and 

cover d with but littl timb r. A ·hor eli tanc north a. t of the ca cade on th 

' outb Fork there i rt w 11-mark: d lateral morain , th fin -t n anywhere in the 

1· g-ion. It i H a .·mooth, <W n ridg 200 f t in h ight, ntaining many round d 

p bble and bowlder:;, often ·triated and havino· a final thin coatina of purui . It 

wa · bordered by wo glacial lob in the 1 of a put· he.'l.ding b tw n loud ap 

aud ott P ak. 

ORIGINAL CONDITION OF MOUNT MAZAMA. 

Thu far the exist nee of an original fount Mazama ba b n a. urn d. Th 

evidence on which thi. a umption i.' ba · d may b briefly ·tat d a. fo llow. : Tb 

inner lop of th rim pre nt · ction of tb brok n lava flow , whi ch radiat 

from the lake and . w re evidently effu:5 cl from a our e high r in a ·b ca e than 

the re. pecti\r flow in tb rim. If the flow. of th rim w re r -tor d to th ir 

original siz by extending them inward from tb rim they would conv rg to a 

common source and make a volcano which would occupy th pla of tbe ald ra 

and make a promin nt peak, Mouut Mazama. 

The peak mu t have bad a crater imilar in character to that_ of V\ izard I. land, 

for it wa the our of much fragmental mat rial p1· ad in all dir ·tion on tb e 

mountain lope. 

The former xistence of 'Mount Mazama is indicated also by the radial dike 

which cut the rim. They evidently originated from pre sure in a ·olumn of 

molten material in the chimney of }1 volcanic p ak ri ing some di tance at 1 t 

n.bove the rim. 
I.J. S. GE<k6oiCAl. SURvrv ~ROFESSIONAL PAPER NO, ! Pl. xh 

A . MOUNT MAZAMA RESTORED. 

13. RIM OF CRATER LAKE. 

DEYELOPME T OF MO T MAZA 1\lA. 45 

The mo-t convincing- e \rid ' ll e of the existence of Mount :Mazama on th ilE' 

of Crater Lak i · to b found in the glaciation and drainage of th rim. Th 

radiating glaciers, whi ch in their de ·cent cor d th cr t of the rim, could ha 

·orne on ly from :t ntral peak. The record of th ic and water drainag from 

thi~ peak in th topography of the rim a re unmi. takable. 

There can be no r a ona hl doubt a to th form r xi t nc of Mount 

Mazama. hut it · .'hape and size ar more difficult to d tcrrnin e. Mount Mazama 

i. compos d largely of lava similar to tho e of "Mount "ha ta, and fron.1 the 

·lopes of that fa.mou p ak w may draw an inf r nee a. to tho e of 1 unt 

Mazarna. Mount ha ta unlike !fount Mazama , d · not . tand on an eleYat d 

platform. It ri e. with a maj -tic ·we p of 11 000 f ct from g ntl slope about 

its base, oTaduall.\' g rowing te pe r upward to th e bold p ale At tb h i ·ht 

of ,00 feet it has ahout tlw amc diamet r a Moun t Mazama at an qual 

elevation in the rim of 'rate r La k . Above thi · Iount ha. ta ri O\'Cr 6,300 

f eet. Th0 p1·ominen of Mount ?dazama a. fL d rBinage e nte r i quit equa l to 

that of Mount ha.-tn , 1 ut it. ,; lop son t he rim of Crater Lake. rangino· f rom 10° 

to 15c.:-, ar carcely as g reat a. tho. c of Mount basta at a co n ·pondino· I vation. 

On tb oth0r hand. the cany n;.: of un a nd and ere ks on ?IJ oun Mazama art' 

mor profo und and hav been much m re deer ly o'la jated than any of tho.·c 

on :Moun t ha ta. It th refore ftpp ar: r a ·onahle to ;.:uppo that :\fount 

Mazama baJ a n a ltitud at lef t a,.: oTea.t, a nd po ·ibly OT'at r, than Mount 'ha ·ta 

(H 3 0 fe t). 

Fr m a larg allloun of data at hand concemin <T th ba. e of Mount Mazama, 

an attempt ba · u n mad to r store it. summit and 1'1. XU, l, illu tJ·ate. the 

re ult. It i pi tured a · it would n w appear. with a mall but d.L tinct o·lacier 

repr ·entjno- tb Anna ' r<' k g·la.cier, whi ·h on e overfl wed the d ivi d we tward 

into the Rogue Riv r drainag . 

From th am o· n ral po ·ition . bnt at <t om wba g reat •r elevation, a vi w 

of tb rim a jt app ar. to-day has been 1 r parcel by tb ·am artist, and i bown 

in Pl. XII, B. 

DEVELOPMENT O F MOUNT MAZAMA. 

·ott P ea k i · on ly n l!trgc ·one adnat' to Mo unt ~lazam L. It belong to the 

·ame ·rntcr and hold · c · ntiall y the ·nme relati on to it :t:;, ' ha ·tina doc · to ba ta. 

Th' :;!opt': of -;\J unt l\lazan1a r ' ach to th e })lains at it east rn base, and it i' ou of 

th e largc;;;t mou ntain.· of th e Ca;;cad l:{Juwe. 

The h g innino- · of Mount l\la?.ama arc now deeply bu ri d b neath th e lava -of 

tb mngc, in luding tho c di ·pia. ·ed o n the lower slopes of the g r at cald era I cncath 

the water of Crater Lake. Th ea.rli c:-;t l:wa:o now vi ibl e rl.l'' th o ·e of th ·outhern 
46 GEOLOGY OF ORA'l'ER LAKE N.A'l'lONAL !'ARK. 

and western la.ke border, and wh n they were erupt d th - volcano wu · normally 

active, ending out with itn stream of lava large contribution of fragmental material to mak the heavy conglom rates of the older portion of th rim. The many 

succeeding flow of and .·ito and lay rs of conglomerat built up th mountain lope 

to the ere t of the rim upon th outhern and we t rn . ide, a.nd ott P ak too, bad 

attained its fu ll dev lopment wh n tb p riph ral v nt·· of ba. nit opened and by a 

eries of eruption built up the urroundin o· country with adnat c ne..: upon th 

outer slope of the r im of the lak . Th n follow d the larg eruption · of da ite 

forming Llao Rock and th northern cr t of th rim to Cloud Uap. The e fl ow · 

occurred during th period of gla iation of M unt Mnzama, and tr am of lava 

alternated xvith treams of ice, a combination ·whi b doubtlo gave ri e to exten ive 

floods upon the lop , and filled the valley · b low with volcanic d bri from th e 

mountain. In onnection with th eruption of the e vi. ou -. lava · (dacit ) there 

were great explo 'ive eruption of pumice, whi h wa · spr ad for 20 mil e or mor 

acros th e adjac nt country. The explo ·i,·e a ·tivity of Mount ·Mazama ·ulminat d 

in the eruption of the peculiar dark pumi ce rich in born bl nde, w bich followed the 

outflow of the tuffaceou dacite. 

DESTRUCTION OF MOUNT MAZAMA AND FORMATION OF THE CALDERA. 

After the eruption of the pumice cam the r evolution whi h r mov d the 

large core and the upper 6,000 feet of Mount :Mazama and gave rise to th ·ald ra. 

Th re are only two way in whi ch hi change ·ould hav b en effected- itb r h • an 

explosion which blew away the top of th mountain or by a ·ulr idencc whi ch 

engulfed it. 

The occurrence of va ·t quantitie of pumi c for a di ·tan e of 20 mil · · in all 

direction · about the ba ·e of Mount Mazama i · evid nc of fl. mo' t tr m ndou · 

explo ive eruption at that point, an eruption th e equal of whi ch ha: not y t 1 c n 

found anywhere el e in th Ca cade Range. Fine mat rial wa.· blown out in m ·t 

quanti tie at the ·ame time and by drainag o·ath red into the utTOu nding vall ey 

which it fill to an extent unknown, a far a. T have b erved, on th e , lop H 

of any of the other great valc.'l.no · of the range. a Tb i · impr ·::; i '' vidr n ·c 

bows conclu. ively that a late, if not th e final, eruption of Moun Mazallla was 

explo ive, and of ·uch magnitude a to sugge. t that th r moval of th mountain 

and the origin of th e caldera may be counted among i · effe Thi:; :-; u<>'ge. tion , 

howeve r, is not ' Upport d by th evidene re ulting from a study of th ted 

material and its relation to th e lava flow · of the rim. The fin e material filling the 

valley , and the pumice throughout its great area, are hornblendi c in chara ter 

a As far as my own ob er vatiou goes the above remarks apply to Lu ·en Pea k, Mou nt u..~ , nt Pill', Mount 

Thlclsen, Diamond Peak, and Mount Hood. 
DE8TRU TION OF M (T T MAZA fA AND F RMATION OF THE .ALDERA. 47 

and wer e rupted in •onnection with th da. ·itc::; of th e ria1. Th ir eruption 

therefor e, wa · of th e u ual typ , and not of th kind which r emo,· mountain . 

As far a.· may be judged from the siz of the pumic dcpo.;it now expo d in th 

rim, the g reate t ruption of that . ort of materi a l from :Jf un J\lazunHt oc ·m·1· d 

before th extru: ion of the dacite of L l::to Rock, and i. c id nee that th grea s 

explosi n occu rred long bcfor the de truction of :Iount Mazama.. 

Ther e i:; another matt r of importance b aring dir ·tly on th explo iY 

theory of the a ldera which rt> nd r that theory wholly untcnab.l and fully orrob -

rate th conelu 'ion deri ,·cd from a ·tudy of the ·hara ·ter and eli ·tril ution of the 

pumice. The lava expo ed on tb inn er .·lope of the rim i: hietly andesit . and 

it r elation i ' such a · t indi ate that s lid beet f nnde. itic lam form d b.r fftr 

the larg-er part of Mount Mazama. If th e caldera r esult d fr om an xplosi n 

thi mas · of a nde iti c flow ·· would hav been broken to frao·men and blown out, 

o a to fall around th cald nt and fonll a rim of frag·m ntal mat rial. From 

the . iz of th e la.ke and the r emaining portion of Mount :Jiazama it i · 1 ibl to 

comput approximately what the .'iz of the rim formed in thi way w uld b . 

Bnt before w can do this it i: ncce sary to consid r the ·ize and ·hapc f the 

cald ra, pecially of that part which li ~ b neath the la k . 

To determine th co nfig-urati on of the hottom of 'rater Lake a larg numl C.l' 

(16 ) of ounding w r made und r th dir tion of Ma jor Dutton, who sunnnarize. 

th r ·u]b a ' follow :a 

"Th i nferr d oofio-uration of th bottom may be ·oncei ved of a a n arly plan 

urfac fo r th roo ·t part, upon \ hich -tand tbr abruptly ri ·ing prom in nc s. 

The Jar · ot of th , ri;;e · aboY the , urfa of th wat r a : d disc lo c.' it lf a. a 

large ·inder Tbi · on ['Vi za r d I ·land] sta nd · near th \\' C' t rn margin of 

tb lake. ~· * ·x· Th other two pr mincnc c ar dis lo- d on ly by the plumm t, 

for their top ar ;;ubmcrg d, on at !t depth of about 4:50 fe t. the oth r at a 

d pth of about 2u feet. Th depth f the fl oor upon whi b th s promin ence 

tand varie from 1,600 to 2 000 f t. At the dccpe t ca::;t.thc wir g::tv a r ading 

of 1,996. To this hould b added ;t smnll but unkn own CO lT t io n for th e str tching of th e wir , wbi h will make th true depth of thi ca .. ' t fully 2,000 feet. 'o 

far n · known o II IP thi · is th decpc t fresh water in the nitcd tatcs. 

On th map (PI. Vl) t.hr 1rincipal :oundin o·s arc noted. From thi ·data, tog thcr 

with information from 1\Ir. \ \ . G. tccl, who wa.· pre · nt when th , oun ding-s w r e 

mad , th pr · nc of two ;;nbla u ·trin eones i · inferr d, a nd it i.' lear that a 

laro·e ma. s of Java pr ad fro111 tbc \Vi zard l ia n 1 ,·cnt ove r tb la ke tl.oor. Th 

g r ftt d pre ·sion toward the cast rn marg in f th' Ja k ' may not ha,·e been fi ll d up 

any after the aldera wns fo rm d , but it i ' c,·id nt tbat the d pth f the w st rn 

portion ha b en g r eatly r ' duced by the mate ria.! rupt d f rom tbe thre smnJl 

«Eighth Ann. Rcpt. . . G ol. Rurvcy, l'nrt 1, I 9, p. 157. 
48 GEOLOGY 1" RA'I'ER L KE NATI :-.'AL 1' RK. 

v nts upon its fl o r. It app ar w II within the bound f r a on to a um that 

1,500 feet i not g reater than th av rao- d pth f th o rig inal cald nt b low th 

present level of th Jak . 

Th area of the caldera , a·· marked ut hy th crest of t h rim ve r 27 

quare mile , and it.· ori o-i nal volumE> . making ::;om a ll wan· - fo r th" 

r filling from the cratc 1·s on its fl oor, i · ftbo ut 12 ubi · mil ·. lf w • 

add 5 cubi · mil s fo r th part of th mountain ftb ,. th cnldera- and thi · i 

a con e rvati ve e ·timate- we O"et 17 cubic mil of material, for wh ' C disappearance w hav to account. If thi mat rial wer blown out by a r at 

eJ>.rplo ion a ncl f Jl equally d i tributed upon tlw ut r -lop of th rim within 3 

mile of the cr t it would make a la_ye r O\' r 1. 0 f t in thi kn Thi ma · · 

·would be so con-pi uou a,nd eom1 osed of s uch frngm ,nt.-'tl t rial that i 

pr ence ould not be a nlfLtter of doubt. Th r ca n be n qne -t i n ·on rning 

its complete ab cnc , fo r the urfa e of tb - outer ·lop f th . rim xp ' · v rywber e eithe r g la ·iated r oc k, glacial mora in o r pumic all of which ar f atur 

wh i h belonged to Mount Mazama befor its de tru tion and no tra f a fmc:rm ntal rim, ncb a i: r fe rr d to abov wa · found anywh r e. 

The phenom na on th oute r . lop of th rim l nd no : upp rt to the \' i w th~1 

Mount Mazama wa ' blown away and the calde ra produe d by a g r at ,·o kani e 

xplo ion. In fact, th y con1 pl t ly negati,· . u ·h a vi w and w ar pn.t ·ti ally 

driv n to th opinion that J\Iount Mazama ha' b n no-nlfed. ~1aj r Dutton, 

who tudi d the rim of Crate r Lake with a trnining gained among th a ti,· 

Yolca noes of the H awaiian I land·, re ·ou·nized the wide di:tribution of th pumi ·e. 

but the ab ence of a wei l-d fin ed fragmental rim k pt him from attributing tb 

origin of th e caldera to a n 2.--p lo ion . On th oth er hand, be fully appr iat d 

th diffi culty of proving that it originated in a .'ub id n ,a H ay : 

" In th H awaiian caldera"> the vid n · ' f . inkag ar eon ·picuou:. Th y ar 

not confined to th deep r fl oor · of the pi but a r al o : n in the partial ·uh: idence of g r at blo k · or ·li ce: of the wall,; immed iately enclosing th .m and in 

irregular , unken :pot: in their vicinity al ·o in 'th mark · of pow rful ·h arinoor faulting a ·tion in th e ' valls them elve_-. They appear to b • correlated t th<' 

rema rkably quiet habit f the H awaiian volcanoe ·, to th ir hab itual mod(;'s of 

ru]:1tion, and to the :;p cial tructure of the volcanic pile.·, whi ch do not ri in 

·tecp conical p ak. , but ar ,·ery broad and flat. t ' rat r Lake neith r in the· 

wall · them eh s, nor in the imm diate n ig hborhood back of th e c rc:t line, h~t c 

a ny trace of .-inkag been olrcned a. yet. otb ing can at pres nt be p in - d 

out which ugge' t.s th e Hawaiian mode of orio·in , hey nd the fa ·t t lmt a va t 

crater i · before us. T b' gen ml , tructur and habit of th Ua!iead' yo] ·ano 

are indicative of a lliOre \rigo rou. ,.;ty le of volcani c a ·tion than th Haw11iian. ' 

" 'cicncc, VoL VII , II!XIJ, p. 1 L. 
DE "l'R CTIO 01<' MOUNT MAZAi't[A AND FORMATION OF THE CALDERA. -!\:) 

L t u · 

width of th 

thtUl llt th 

xa.min ' brieft.) :>omc of th e po ' ·ibl condition · of engulfment. Th 

ea.ld ra aerO ' S th ·t of th e rim i,; al out half a mil rrreater 

h 

leY l of the lake, and Mount Ma;~;ama could not have ,; ubsidetl on 

the pr " nt inn r ·lop of the rim a.· on .·olid ma:>.' without profoundl y ;-; plitting the ri111 at one or 111ore poin ·. No suc:h e ro:;:s fra cture:-; of th e rilll h~L,. • h t' n 

oh:-;l'ITl'd. " The mountain , th r fo re, appear to ha\'e co llap:scd, one part aft 'r 

anoth r in ,.; uec .··ion prol ably from the c nter outward a · th e :>Uj port \ntH 

l'l' ll!O\' 'd. The pres nt inne r lop of the rim may not in a ll mve,.: o r e1·cn gr· ne rally hr th • ne formed at th time of th collap e. In ::;om ca · . , how r. th 

inn e r slop wa:-; formed at that tilll c. Of thi' we haYe evidenc:e in the heha1·ior 

o f th liow at Rugg d ' 1· st. It wa · on of the final fi ows f rolll th ,.: lope of 

-;\io unt Ma:~.ama. Befor tb ·pntral portion of th tiow, wher thickc -t. had 

congeal d within th ;;olid c ru;;t, Mount Mazama . ank away and the y t vi · ·ou · 

hLnt of th midd le portion of he ·tt·eam fi owed down o1· r the inn r lope of 

tb c ande ·iti(' ri111 into the a ldera.. Thr liquid interi or of the fl ow ba1·ing 

withdra~m . th erwt eav cl in and formed Rugged Cre ·t, with it peculiar chaotic 

,-all y of tumbl d fnwm nt.·. column:o< and bluff. Othe r explanations of the 

p uliar r e1· rs d fiow of Rugged r st haYe been ourrht but with ut antil. 

The fa cts arc :-;o ,.:imp! and .·o direct that th y app ar to preclude any .oth r 

hyp tlll':'i::;. 

lt would )p app<tr nt fr m tb fa k al that th llap ' ' of the mountain 

\\'a" ~~t I ast mod rat ly sudd n, for it i.· no at 

'r ,...t fl ow ' as lotw c x1 o · d before r aching th 

the t"allem b y ond. 

all pro! able that th Rugged 

pr ent le~· I of the lake aud 

\\ c may h aided in under.·tanding th rig iu of the ald m by picturing the 

t"o nditi ns that mu:-;t have· cxi ' ted during th eruption of th e Rugg d e~ t dal'it 

from the upp r slop of )1 unt Mazama. At that tim a column of m !te n mat ria l 

o~ in th int rior of the mountain until it ,-crtlow·d <tt th SUJllmit, o r buL_t op n 

thl' side:-; and l'.:!tHped throtwh th<' tis' ure. The r ent of tb' monntc'lin :-;id wa · aused 

in :-~ u('h l'HSl':-i hy th pr ssurr o f th column of 1nolt n mat rial it in clo,.:cd. Th 

ntolt ' n lavas he in u· heal·,,- the pn'.· 'lll'l' o f the <"Olumn within the monntain WI\.' very 

great, and in ·r a:-; ll rapidly with th ' h iu·bt of the ,-obtn . During tho final a ·tivit,r 

of Mount ::\la:.mnta thPn' mu: t ha1· ' !Pen within it a <:o lun111 of !ant rising to <l height 

of v ' r K.oon fe •t above th o h;t.,;o of tho Ca ·cad Hu.nge. lt is po:;sibl thut thi.; 

1-P'Ntt pre~ ·u r :Lided p 'rhap · by :-iOllt tbe r for · ., made an op n i ng form d low 

clown upon th mountain :; lope ullowitw th la \'H to cup The. ub id nee of the 

hwa. within the ntountain 1 ft it 11n:upported and nw: d its ollaps . Phenome m1 of 

!)255- No. · - 02- - 4: 
50 GEOLOGY 1<' CR.A.TER LAKE A'riONAL 1' RX. 

this ."O rt arc we ll known in conne ·tion 1 ith th e twa,iia,n vo iC!lllOCK. Tn LX·4-0 , 

according· to Prof . . T. D. Dana, th r' was an -ruption fr m th ·loJ c:o; of Kihtuca, :ti 

1nile,. f rom ;tnd over · 000 fr et be low th 1 ve l of it ' tunmit. \t l ilnu ea tiH· 

·um111it of th hw;t ·olumn i.· w II c.xr o eel in ;t lava la,k . Jn ·o nncctio n with tlt1· 

c rur tion of L, -1:0 th e ht v;t of tho lake ·nb .. idecl to fl depth of 385 feet, and tit irregular 

1mlls :-: uiTOu nding it w r left without support and broke off and fell into tltP mo ltl'n 

111atc rial below. During tb intr rml:-: brtw 'e n th' eruptio n:-: of Kilauea Lh molten 

colulllll risr:-: toward tit ·urfa ·e only to hr 1 Wl'r d by Rubs (llll'llt l'llpti o n:-:. TIH' 

s ub."idenccs, howt'V<'I' .. arc not a lway:-: ;t•companicd b.'- :tn outlio w of la1'a upon tiH• 

." urfatc. At othe r times it may g ush for h a:-; a err at fountain hundr d · of f et o · 

mor e in he ig ht as if dn dir tl.) to hydro,.tatic pres:-:ur . 

That M ount N!azamn: eli ·app ared a,nd the ·:ddr r a, o ri ,·inatcd t hrough Ruusid IIC(' 

.' em · evirlcnt. b ut th • · lTC ·ponding ffu ·i n upon th surhc , if ." lit h vcr 

o ·currcd ha · not y<'t be n found. It i.' bar lly ·on ·c imbiP thnt 17 <'ub i milr:-: 

of mate rial much of it oli d lava. c u ld collap,.; , h a ·ain m It d a nd . ink away 

into the a rth without a. cotT lative e ffu.·ion at :-:ome oth r point. 

Th bottom of h ·a.ld ra at its de p e. t portion i:-: ;tt an e l vntion of ±,200 f · ' I 

above sea level aud it is not to b expect d tt th point of ~c ap w uld o ·cur 

at a ny. hig he r I 1·e l. Klamath Ma.r;;h, whi ch li sat tlw ea;;t rn ba.s f tho 'a:-;vad1• 

Range, i · over 200 fe t hig he r than th bott m f th enid ra. Tbi. would indicab· 

tha tho tru ed ma s ·hould be ·ought on h west rn ,.]op of t h rang , wh r · tl1 · 

-1:..:40 -foot f'Ontour occurs along Rogu ~ RiY r. at IL di. tan· of I ss than 12 mil . .., 

from th rim of th e lake. The corrl:' lati v ht ,-n, might p rhap,. b • xp ·ted to he 

da ·ite. clo ly r ela d to the final fl o w of )'Jount ~1 aza . but on Rog ue H.iv r tbt 

hwa ar e D"e ne.r:ally ba. a lt. and the re is no :-; uv<rcstion o f the scap 

cnormou mas of hwa a·· r · ntl _r a.' the t ime o f tbe U" rcat ·olhtps . 

of :-;u ·h a n 

Wh th r o r 

not w are ab le to di;;co,·er th e corre .. r o nding A'ut; ion .. th rc ."C m.· no r a:-:onabl 

do ubt that Mount .Mazawa wa. one a r ality and that it wa~ wr ck d by ncrulfm nt. 

CRA'l'ER J ... AKE. 

TEMPERATURE OF CRATER LAKE. 

Among tho ·e who i .. ited 'rater Lake with th' Mazamat; in 1 !16 wa.· Dr. Bartun 

, V, E1·e rumnn , of tbc nited , 'tate Fi h Commil'lsion, wlw made ."O IU C obsrrmtion:-; 

on it." t mperature. H e r eport d that on " Augu t 22, at a ." tation a.bout 2 111ilc · e:d, 

fro111 th ."Outhea t corne r of Wizard I. land * .,. ·x· th e surface temperature 

wa,.; 61 ° ; at .L depth o f 55 ~ feet, 39° ; a t 1,040 feet, 41 ° ; and a 1,62:3 f eet, whi ch was 

at the bottom, 46° . ' ' " H e fu rth er remarks that " If th · I' b 11 0 cnor in ou r ohs nan ) la zama , \·ol. I, ::\o. 1, p. 232. 
TEMPEHAT BE OF RATER LAKE. 

tiu ns. ~> 'e lll:; ce rtai n that the ll"aten; of 'r·ttcr Lake :trc stillreceil·-

ing l1 a.t from tlw ro ·ks upon ''"bith they ·r est.' " Hi.· b. · l"l'ations 

wcn· ma.ch• with a X g r tti-/jam hra deep-s 'a thermometer, tripped 

],_,. lliCans of a prope lle r. Dr. Ev'm mn n iol}L,\' ·:a 

' 'I'll o nl y pos ·iblc :;oun:e of e rro r which ha: yet . ugo·est d it.-.; lf 

is tha.t the propel! r nmy not dway:-~ ha1·e wo rk d ]Jroperly . lt. is 

po:,;:-:ihl e that, in sO illC ca · s. whcn web gan haulinCJ· up th the rmomete r the propell e r fa il d to r l'en; until . ome mom nt:; late r. in 

whi ·h ta.· the rend ing· would he that fo r :omc d ' ptb other than the 

on de ·ired. Tbi: iH a po ·.- ihili ty, thouCJ· h it .· m: to m improb}tble. 

The ob.- r vation · ·bou ld 1 car fu ll. · rep ated befor e the conelu ions 

ugge ted by the rc ults should b a ·c pted .. , 

The vo l ·anic ro ·k of \\ izard l;;land, a lthough r cent, arc ·uffii ·ntly old to have tompl tely cooled ofl'. There a re no vi ible fuma -

r lcs or hot ;; pri1w:-~ anywber ab u tb lake. to indi('}l.t local 

r mnan b of Yolca.nit' heat, and it wa.- not exp t d that the bottom 

wat r would b \ntrmer than th e main body of th lak . D r. Evermann·. ob" n ·ation · suo·g t that th point f late t volcani c acti\rity 

on th floor of tb · lak i.· now b n atb it;; urfa e and pos ibly n ar 

on<' of th . Lw t·on s loettt d by th t' ;;ou nding ·. II mad only 11 

sc ri s of ohs n ·ation;; t d pths b yond 5 f t. 

To scttl' t.hi.- nmtt ' 1'. if po . ibl c, · v ral th rm meters of the 

L"Oilli1JOll f rm. hut with th ick vla~.· jack t · to withstand pre · ·ur , 

w r htain d fron1 Jamc;.: G re n. of Brooklyn, and a r el bavino- n 

nq id wi nding attachn1 ent was rr I ared fo r their manipul ation. 

fl a.rd-d rawn tin n d-st' I wir . Xo .. 0-:1::2 . wa · found b ·t suited to the 

work. Ea h Lh rm m r wa: p lae d_ in fl I rote ' ting bra tub ( 1n 

fig-. 2). lo:; d by a p rfomted ru bbe r co rk. Rnd placed in R ·ylindri cal 

hu·k tB, ' f inch:; in diRmrter,h1win ·a n npwardop ningvalve ~Lt 

eavh end t nllo' th wn.t r to pn.:;s th rough whil ' tb 1 u kct wa · 

descendi ng. but to hold it confined while• R8t'nding and thu.· not 

on ly preserve tb t n1perature of tlw the rmom tc r hut at th ·:un 

ti nw to fu rni:-:h a ;;ampl e of' tho watn frolll any d pth desired. The 

sf one [) a nd do u blr hook E w r e r l a;; cl from the susp ' nd i ng har F 

at the ' nd of th wire wb n tb bottom was struck. Loop.'-' w r c 

pla ·cd o n the wir Rt int tl of .-o feet, ·o that :eveml th nHometc rs could h .- nt d wn at the .-nn1<' tim . fter loweriuo· the 

tlH'rmomctrn; they w r e mo,· d vi<Y rousl_,, up and down fo_r n, few 

111inu tcs to fill ach cylind r with water. They w r e allowed to 

rcnmin th r e for half a.n hour to make it ure that th thermometer 

nOp. dl .. p. ~:1 1. 

51 

A 

1 .· 0 

F10. 2.-Thermomotc r 

nncl attnc h m on ts 

used nt rater Luke. 
52 GEOLOGY o~· CJU'rJo:lt LAKE NATlO AL I' RK. 

in each ua · h~Ld acquir d th ' t tnp ' mture of the pine<.'. The t hc nnont etc r;; w ' I' 

rai:'d as mpidly a po · ·iblc anlrcad n.t the su rface. 'L'h <.' thc rntomciA'r f r m a dep th 

of o,·er 1,900 fe t reach d t he : urfa ·c and wa>~ r ad in I ::i.' thnn + minll t s. ExpPrim nts showed that by chruw ing th water in th c lind r a~ not d aho \· ' th t h ' 1'-

momet r read ily acq uired th waters temp ratur bu with n thrcs clo:-;<.'d and wate r 

confin d in the eylind r, a:; wh n a,; cndino· rapid!.\·, the thc rm 111 t r was antply 

protected f rom th influ ence of the hi o-h r temp mtur o£ th ' . urfacc wat .rs. 

In ord er o limit~fLte the ·lmn · . of fa ilut· a far as po .,ihl w obtain<.'d front 

t he U nited tate:-: F i ·h Com mi ·. ion th roug h th kindn ., of D r. g,. nuann n 

1'egretti-Zambm deep- ea thermomete r tripp d by am " en er nt I wn t.b wtr . 

H e f urni: h d us abo then c s·ary apparatu · for using th th rn1 m t r. Tbi 

the rmom te r and tbe ordinary form noteu abov wer <.' · nt u r a nutnber of time:, and in vari ably n,grced wh n brought to he snrfac . Tb N gr ttiZambra e\7Cnt l time· !dlowed th me · nger to pas th ·lip wi thout r<.'n r. ing, bnt 

wh n r egi.-tered here i. no dange r of cha ng by :mrfac Th two 

fo rm: of·th rmomet r. w r generally us<.'d on th ·ame wir 5 0 feet a1 a rt. 

Ob ·ervations w r e made nt tb r c wid l.r s 1 arn,t c1 p in · to <t depth of over 

1,3 0 f eet, a nd the r esults ar g iv n in tb a<:company ing table. Th t mpcmtur 

of the lake everywh r below a depth of 300 f · t i: ap1 roximately 3~ ~ anu tb 

bottom contain no appreciabl volcani c h at. 
JOU 

:!00 

400 

r.oo 

H7:2 

1, 000 

1, :30o 

I, 442 

1,41:! 

1 H42 

J<:) fP ~AT l RE OF CRATE R LAK F: . 

'l 'eiiiJIPI'((ltwe of r'rnle,· L.tke. 

I. 2. ;{, 4. 

fh'IJI'I'P.< . y,.eP . 1 >eyrt'l'8. J) yrt P.~. 

4. 50 .'">1 ,)0 

,, an 

-------- -- -- -- ---- ---·-- ---- ---- ---- ------ ..... . I 

" :{H 

( Hott onl. ) 

(I ;{\) 

(I :{8 . .'j 

( Hot tom. ) 

0. 

I )f'f/l'fFR . 

!12 

".Jz 

'' 40. ?i 

I> ;)!), I) 

(/ :{9.;) 

It;{!) 

(/ :3!l 

( Bottom.) 

53 

o Commtm form ui th ermom eter with thi<·k ,!.!In,-. j1u·k eL inc·lo:-:erl in hm ~ tuh<' 1111d :-:n~ f• tHl rt in httC'kCL :l! b~

12 inrht'f:, 

/J grl'1ti Zumbnl flCCI>--:- ·d thcrmom •tcr. 

:-:o. I. .lnty •. t!l01 , ~II . Ill., I mit toward iRioml from Eng!~ C.wc. Tllcrmom ter flown 30 millll!C': roi~cd from 500 rc~l 

in :l minu e~. 

:-:u. ~- Jnly •. t901, 9. 10 n. m., t mile townrd ishmcl from Eagl OI'C. B th common form nnd X 'grctti·Zambn< orenL !own, 

bul m ... . ~ ngcr foi led LO trip :'\rcgrc.•tti-Znml ra . Down 30 winutcs: raif.:cd in 4 minute.~~:. 

:\n. :t Julr , 1901. 10.50 a. m. , t mil t Wllrtl i•land from &tgl o1·e. Thermomete r clown 30 minutes: l'ilised in 5 minu tt·' 

from 1,306 fc~l. 

X<>. I. .lul y li, 1901, .-10 a.m. 'onr d eep "t P>HI of lnkc, wh cr line fr m Dutton 'lifT to lcetwood Cov rn-<s ~ti e from 

to11 o f ind •r on , on WiUil'd Island, t 'I ud np. Put mmon f rm at end of wire nnd Ncg-retti·Z>lmbm .'\1. ll 

f ·et highe r. nt common fonn d own first to 1,000 f c t; le ft down no- half hour und rn iscd in I minu tes: th ~11 

sen t t bollllm-1,942 feet- with Negretti·Z>lmbm nt 1,+12 feet, nnd bottom <'" Clll'ne np in 8 minntl's. 

:-: ... n . .lnly 19, 1901, 9.1011. m., i mil e sou th of Cl elwood ov . nrfnrc tempcrntur . 52"; buL nl 10.~0 it wn. rni cd to i"i 0 . 

At 972 feet Ncgr etti·Zambm fnil I to trip >tnd r giste r. This lru t series was ob>' rvcd by Jnme.' torr>; ft lld E. II" 

n cr hberg r. 

It may be n t d al o tba.t rate r Lak althotwb ov r 6,000 f t abov the ::;ea , 

d .· not f r z ov r in wint r, a:-; d th Klamath lak at iL mu h low r (c,·el, upon 

tb<' <'a,.;t rn ::; ide of th m untain. Mr. E. \Y. H er chb rgcr a tmppc r, ' fi.W rate r ~tk 

Mar h 1-. 1 ~v, ' ith ut ice. The w in t r' a · v ry !Old. \.t tb ;;:am time Diarn nd 

L uk n.nd th o Kl amnth lake· r cov r d with thi ck ic . Jl Raw th lake naif a. 

doz 11 oth r t iiJI • in the d pth of wint r fr m the a:t and n v r not d any i e. On 

F <'b rtmry l ' . 1900 h ::;aw th lake from the we ·t a nd not d ice ,. r t h s hallow 

w~Lt r hct1 n th j land a nd th w st . bo re, but none ;-Isewherr . A lthouo·b th e 

lnko i,.; »I way · pen Mr. H r eb berger n ver . aw n.ny water b ird o n th la k in th 

winter. CHANGES O F WATER LEVEL IN CRATER LAKE. 

n xamimttion of one of th etlllmyed bore · of ' mtc r Lake tn ug u;;:t o r 

S ptemhpr will l'O II\'ill<'e anyone that th l!Li' <' chnnge:-: IE'I'C' l. Late i11 .h11tc :L li ttl(' 
54 GEOLOGY Oft' RATER LAKE ATIO AL 1 ARK. 

ru~ta ean Dapkm'a Jnde.J.· jJulicm·ia, ·warmn a lono· th' shor <tnd attracts oth0r 

minute form · in nbundanc to the >'amc pla<:'. A' bite tl po:<it conq o,.;t' I of tlH 

r c1nain.· of the · ' oro·;tni:ms tnark,.; th ,.;hon' lin at the upprr limit of th ' ir <Lhundant 

appca ra n e, and as t he season advan ·cs low<•r I ,-cis ft re nmrk d in the s;U1J t' way. 

During the summer, wh n there is ra1 id va.p mtion and I itt.!' or no preci pitation. 

the :urfacc of the lak ub id , lut du rin · th' rainy wintt'r it ri. ('s n.gai n. Tht> 

oscillation i.- limited to about -:1: feet. Th rising <tnd th sinking hn.lanee ca ·h otiH'l', 

so that the lake ma inta ins in g ne ntl ncn.rl. th sam ]e,·cl. o ol>s rn\tions whatever have been mad when th wat r wn.s at i · hio·hc:t sbtgc, whi\'h is s uppos0d t.o 

be early in May, but th lowe. t turn ing point wa.. r a h d in lH01 nbout th lst of 

0 tober. The hio-h a.nd low poin vn.ry fr m yea r toy ar with the :-Jt'Hs ns. hut th 

change i · o g radual and on t he whol so ·mall that di tind hen. h l!'v!'ls arr not 

cl vcloped. The lowe -t wate r known wa · ob 'ervt'd t'ptemb r :26, I !"1:-~. when jt ' as 

lc:: than a foot below iu I v I on pternb r 15 1901. 

Augu ·t 22, 1 96, a gag ., a er t d on the .·bore of ra r Lakr, for th .\J aznma ·, by . H. hol e·, pre:ident, a nd Earl M. Wilbur :; cr tnry. Th t' gag wns 

mad e of a board 51- in bcs wid a nd 10 f et lono·, with scn lc :ubcli ,·idcd to t0nths of 

a foot. It wa nail cl to a log ext nding fr m tb >'hor into th wat0 r, :wei zrro 

of th cale was p la d ju ·t -:1: f t b>n ath tb wat r sudtH.: <' thuH nllowing tlw wttti'J' 

to sink f feet wi thout lc.-·1x in o- th . a le. A coppPr p cket fast0rwc! to th uppc•r 

part of thf' gage contained a reco rd book, in whic·h i:itor: at tbc lakl.' wf't'<' ;u-;ked to 

not the h io·ht of the wate r. Fearirw that thi;; fragil<' o·agc' mio·ht not cscap<' ll('<·id nt from rolling ·ton or .-licling . now, "\L "\Y. Nick r:on , of Klamalh Falls. waH 

rcqu ted to in:crt a bolt in a cliff ncar the gage an<.l car fu lly detcrmin <' th h e ight 

of the l olt above the wate r and r ead th gage. In the n o rcl book , ' pt m bcr t f , 

1 96, Mr. Ni ker ·on r ecord · th he ight of the water on tb gage 8.42. , and Hdds: 

"AI o trengtbened the gage, as r que:t0d by M e .. r.-. Dill rand ' ted and put ttp 

copp r bolt 5 feet to th w t of the O'ag at an levation of .- . T feet al O\'f' the 

pre. nt level of the watel'. ' The gao-e wa · broken of:I' duri rw th e fol lowincr wint<'r 

and ca-t adrift on the lake. 

Augu. t 13, 1901, Jame. ' torr. and Fred. Lar. en, whil making str eam m asur<'-

ment...;, fou nd th copp r box containing tb r cord hook in 5 f t of wHt r ~dono· th<' 

: !tore of Dang I' Bay, about 3t mi le;; cast of Ea.o·le co,·c, wh rc the o-ag had IH'<'ll 

o. tablisbed. The r cord w r w 11 pre rved in the book, notwith: tanclirw the ti1· 

yea r. ' soaking and nabled us to find Mr. N ick t·:;on's l o lt an<.l rrcstahl1: h tlw 

Mazama gage level. We· painted tb :cal . hown in Pl. XIII, A on a ro ·k a bort 

dt ' tance nortbweQt of ickerson' · bolt, ancl add d a. cale al o on th e rock ntaining 

tb bolt, the rock at the la t place being too rough for :mall div ision . Th zero of 

the. seal · bas the am level a · that of th Mazama gag , ancl all known reading. 

of the lake level have been r ed uced to that . c·ale in the following table. 
A WATER GAGE, CRATER LAK E. 

1$. RAFT AND EVAPORATING PAN. 

CHANGE ' OF WA'J'ER LEVF.L I RA'I'ER A KE. 

Water level of rnter fAke with 1' .ference to cale established /,y J{ ll11lCt.~. A ugu.,t fU, 18.96. 

Date. 

1-\<•pte rnhc r 10, 18!12 __ __ _ _ 

~eptemhC'r 21l, 1 !l:~ _____ _ 

A ug u. l 22, 1 !lll ______ __ _ 

August 30, 1 !l6 ________ _ 

,'eplember-!, J 9{1 _____ _ _ 

• 'cpt mbe r 5, l 8!l6 ___ ·___ _ 

l" •pt miM l:~ I !l(i . __ __ _ 

1-(pplemh ·~.i, !11l ___ __ _ 

A lll!ll~t I, I H7 ________ __ 

-.July 1, l90L __________ __ 

Jul y 20, l!lOI. __________ _ 

A ugu t, I , l. 0 I __ ____ __ __ 

AuguR!. JH, HlOI ____ ___ __ 

RC'ptrmb('r 1, 1\101 · · - -- --

, 'cpt m lx-r· 15, 11101 __ . __ _ 

Octo her l 2, 1 !lO I _____ __ _ -' 

I 

H e ight nf 

wate r. 

Peel. 

.Henrarks. 

~- H 2 Mr. F. \' . 0 1·ille found " . H . H e rchl rgC'r,, pt. 1,0, 1, H~ " · 

painted on ad tac.: lr C'd bowld •r a i w yard. e~ t of hoal land -

ing, a mi r rt~ that Aug-. ·1, 18!l7, " tlw low r e nrl of till• \1 

was 71 inches be neath t he nrfa ·c of the Ink . " 

2 . .'\2 ~Jr. F. Y. () ville foun 1 "Dr. lGrchg , l lealh Kir·r hge .. -

ne r " a painted on a ro kin plac a. f w .ranis ast of the landing, and ,. ports that "t.h lowe r part of the II was r inl'i1 · 

beneath the. urfa cC' of th ~;> lake ." 

4. 00 C. 1 L • 'holes anrl Rarl M. Wilbur, president a n I e<' rary of th 

:'>1azamas, tl~nd , Oreg., e;Jtalli heel fo rth ' Oc iel_,. a woode n 

gag . Ze ro of I h ,. ca le I\' :I ~ feet he neath the ' llrf<U'(' uf the 

la ke." 

=~- !10 (The r cord 4.9 ;;hould id ltl~ be :'l.!l, !1." the lakC' ;;urfa<·<• 1\' llR 

inking.) 

:l. , ~5 J. · . .f) ill r, obsen ·er. (Rate of fall n day for :~ a_v~, .O L:{!) ioot. ) 

:l. ~0 E. H. Ba rrows, ob:erve r. 

:{ . <>00 Thoma." ro x ton, b:C'rv r. 

:l. :,!:\ " -- \\' . ~ii so , oh::e n · r, wh •l fixed holt in rnl'k 11 C'~ t ol gage 

and 9.175 f t abo 1· ze r·o f :\Jazam<t se<d '· ( Ratl' <lf fall a 

day for 3-! day>', 0. 16~) fo t.) 

'i'i F. \ '. Co ville nrade a nrark "3 ft. " o n r C' k 250 yard~ cast. of f ot 

f trail an I anoth r "c" o n a roC' k 60 yard~ 11· t f tr·ail. 7,ero 

of ,·ill ~ca e=-L77 of the :'llazarna ~a e. Th r mnant of 

ha ~ b::; id d ron.·id e rab ly . in ·e :'I I r. 

-!.!l05 

-t 61 :~ ( Hate of fall11day for19rlay , 0.0155 foot.) 

L~~ E. \\ . 1-1 r hhe r1rer, ob~e ·e . (Hat f fa ll a. day fo r· l~ day , 

0.01- fool. ) 

4. 11 E. \\". 11 r hh r~ , obs, rve r. (Hate of fall :1 day f r l il da~·~, 

0.0266 f ot. ) 

:t\12 K W. lfe rchbC'r)!l'r, b~ rvcr . (Ratr of fall a day for 1G d>t ·~ , 

:3. 39 

0. 011 ' foot. ) 

E. \\" . . 1-I e rchb rgt>r, ob~ rve r. (Rat e o[ fall a dn.1· fo r H day~ , 

0.0~ 6 foot.) 

E. \\' . H rl'h b rger ob. rv r. (Rate f 1"iRe H day fo r 2!l days, 

0.0051 foot. ) 

Ave rage rate of fa ll from July 1 to.' 1 t.emb r 15 (77 days), 0.023H foot per day. 

uThcs murk• c·ould 11 01 he found iu July, J90J. 
56 OlWLOGY OF RA'l'BR LAKE ATl Al• 1' H.K. 

, wnmary of jlw:lu ttion.~ of ·ate-r TA.tke. 

.P ri fl. 

1R96. 

Au . 2:.. to . eptem ber .J ..•• •••.•.•.•.... . •••• ...• • •. . . .••• •. --.------- · ·-

, 'c pteml r .J to , 'ept eml r 25 . . .......... . .. ... . ...... .............•.. . . . .. . 

1901. 

Jul y 1 to Jnly 20 ........ . ........... . ........ .. ... .. ......... . -... -... ----

Jul y 20 to Septeml er 15 ........ ... ........... ... . . ........... . ... .. ... ---. 

A vC'ragc for ....... ..... .. . . .. . .. .. .... ....... .•. ............... . . .. . .. ... . 

~umber I Hall' of of ay~. fl ub. idencl'. 

21 

Ill 

fi 

111 I 

0. Ol:{fi 

. 01 !10 

. OHifi 

. 02:3() 

. 0179 

At thi<:> rate in 36- days it would .·ink onl-' fl.58 f C't. i. .. 7.' in{' he:--;, whi <- h iN 

much ll101' than the annual pr ipitation. HowO\'C' l', in thi,..; l'OilNicil'mt.io n it mu,..;L · 

b r emember ed that th rate of lo. noted i · ntirC'ly t o g rea for tho wint r. 

when evaporation i · much . lower than in ·urnm r. 

No po itiv ,·idenc hall been ob~ r ved n,nywh en on the inn r :--; lopr of t hr 

rim thrtt the lftk c wa.- v r con idern.bl} high r or lowr r than it i;: to-day. Thr 

compl tc ab.-enc of bench lin . ab v th se of tlw prr,.;r nt lr vel of thC' lakr i:--; 

<-o nelu,..;i ,·c that the lake n \rr r :--;tood highe r, hnt mark:-; o f an_\' kind a;.; lo low r 

le\'el. · would h fl nhtn rg d. The ::; horl' lin n.t nHLll\' p int,:; i;: a. st< Pp hlufl' of 

roeks, hut' at many pia· ;:, sp ially nt tbc fo t of ;: nJ<tll oTtl ebc:--; of whi ch thr r 

nrc fL g reat many, rm a.llu\•ial ·one shall o' ,; the Wfttc r , ufii cirntly so thfl.t thr hottolll i.· vi ·ibl for n nrly 2 0 fe t from the ' atcr's dg . \\'herr wid st th<'sl' shorr 

dcpo"its ar r ln,ti,· ,ly a ,-pry narrow frin o-r about th mat·o- tn f the htkc making 

only a ·light should r on the ·teep ·lope which extend · fr m th top to thr bottom 

of the rim. 

It may b of . uffi i nt inter e. t to warrant m ntioning her c rtain misleacl in oviden ·c which may app ar. In .1 96 a tr e wa.'l found near th wrst sho rr of 

'v izard I ·land tandino- er ct in 37 f eet of wat-r. Tho trunk was hrokrn off just 

abo' c the wat r level, and the roots at the ba ·e w r · n through th clrn r W}LtN 

n th bottom a. if the tr g rew where it was Htitnding. It cou ld not h sh<tk Pn 

from the boat, and it wa.- ident that if the tr r u-rew whe re it wa;; standing it 

pro,·ecl the la ke to hav been much low r than now at a r ec nt time. SuA·i ·icnt 

I aling wir wa.- s cured to rea ·h the hor , a nd it wa. di. covered tlHt.t thr tr 

had no hold upon the bottom. It had d rifted from th e shor of th island. In .Ju ly 

1901, the .-arne tree was off the north dge of the i.-land, at 1 a ·t one-fou rth mile 

from i po ·ition in 1· 96. Owing to the ·teep slop .- of th rim a treP frequently 

slide. into tho wate r inan e r ct po.-ition and th e lowrr part be oming water-logged 
l<~V APORA '!'ION FROM C'HA'l'Jm LA KF.. fi'i 

it float>: about the lakr with o nl · a few feet of the top proj<'rting ab n tlw wnt<'r. 

and tllltll fumishcs a .'pecta.cle ·u ri ow; enough to Cx('it<' tb c imag~i nati n. 

EVAPORATION FROM CRATER LAKE. 

Th e h~ IT ations upon th o. illati o n:; of the lak stt 1fa ce rtppeared to show n 

' gTNttP r loss o f wat r tha n would he accounted for b.'· evapora t io n a lo ne, hut to g·p t 

111 01'1' dPfinitc drtt.'L ·one· ming th matter fLITRngements we r mad to dctermiiH' 

app rox imatl'l.)' the rate of e vaporation o n th e la kn :<urfa('c. For tbi .. purpo;;e :t tin 

P\·aporating p~m 1. in ·h :; quare and () inchl":; le<' p wa · u:;ed. To a,,·o id th bright 

r<'fh' tion it:· in id e wa. painted dirt b1· wn with pitch a nd oi l. 1t wa. >: npportC'd 

o n a raft (Pl. XIII, B) . o that th lower part of th pan wa ' in the water o f 

t hP lak . Th raft war fLnchored in a n 01 n !Jay where t.he wate r was 7 f eet deC'I 

artd fr<' ly agita.ted hj th e wind - hut th way >: did not mo\·e q ui t<' so hig h a o n 

the' la k<'. For th i" I'Nt:;on tb c ntpomtion from th e pan wa:; po. ibly l ss than hnt 

of th e hk . 

Th<' follow ing table g ive>: th e ob;; rvati o ns mftd<' a th <' lake in 1901: 

O&servatio, l.~ of eroporulion ji·mo ('rrrtel' I .ak . 

T 

Time Amount o Tcmpemtnn'. 

I hill'. Tim of ob-

;<('rvnt ion. \\'at 'r. lle ight f wa ter o~ t 

of wat r. xp - by e,·apo- emark~. 

sure. mtion. ir. 

Lake. Pan. 

/Jpyx. /)l'fl··· /)g.~. I Feel. Day.•. Pen. 

,J nl~· '····-- 1:1.20 p. 111 . .i :1:.:? ;z 0.420 

H ...... 1:2 ii p. 111. •1( iiZ . 

. 0 ~]() 0. 01 FillE-d to 0. +2. 

!1 ...... :t20 p. Ill. ii 56 60 I . ~Oii 0 Ol; 

II .. _._. 2 p.m. IH !)~ tlO .~ 0 2 0 02:'\ Filled toO.~~. 

J:L. __ ,, a. m. ' ~ ~ 0 ~:10 :2 . 02 

J(i 0-- 0- 0 fU!O:t.ttl. 52 8 iiO 0 ~f10 :; I . Otl'! Di. tnr cd hy b rood of 11·ild 

du<"k~ o ~rood. Fillpd 

to 0. ~I. 

I i ... __ . 1:.:?.11\ Jl. 111. iiii ~8 i'i~ 0 ~00 I . 01 I Fill('tl to 0. :2 . 

:W ...... ~Ail p. 111. !'\R .'\:2 iill . :{Iii ;{ . i) • 

To !.a I .. _ . .. ... _ ... _ . __ .. - ..... - .. - .. - -- ·l 

I 

- 10 . 12:) 1 (Outitting nbPE'I'\'ationR of 

I Jnl~· 16.) 

J -

Dnrincr the' fhty th ' n.ir and th'e wn,ter in the pan hecanw warnlCl' tlmn th e water 

of tlw la.k<' . nnd d urin o· the nig ht tlH>.\' h cel\.lllP c·o ld r. Twic a chty thP t mp .rnturP 
5 GEOL Y 01<' OHATJm IoA KF. ATIONAJ, PARK. 

of lake, air, and water in pan agr d, hu t g'n ' rally thl' t tHpc ratun' of tb water 

in th e pan wa,; n ar r that of the ;tir th1w was that of th e la ke. If the amoun t of 

Pnlporation i · in larg m asurc propurtiontd to th lilfer cncl' of t III(JC' mtun' 

I tween the air a nd water, the rate of entpomtion from th la ke' 111u -t bav<' bee n 

OT at r than from the pan. Howev r, it i;.: b li ved that the hi uh r temp mtur s 

of th pnn water und r the dry :-;urnnt r ~t osp e of ra.t r La ke mo re titan 

connterbaJnnced tb0 ff ct of oTca.t r tPmpPratur difterener. and thn.t thP rate of 

vaponttion f rom h pan was a.· oT at a:; that f rom th ln.ke. 

Th a.verag e,·aporation fo r thP 10 day~ ' record n ·ed is 0.0125 f 

t thi · rat p r tUlnum the vapora tio11 would lw ~ inC'h c,;. During c· loucly winte r 

weather >vaponttion i;.: much r edu c l, so that 55 in b ,; must I great r t ha n t he 

a nnual rat . 

Prof .·sor Hu · ' II in hi mapa, make th vaporati n p r ::tnnum forth ratrr 

L ake region about :1-6 in ch .-, which appear to b a cl ·- approximati n. 

Obse rvation · on ntpomtion w r rnad al o in camp n the rim of -'rat r Lakr. 

Tw pan: 13 inche,; .'quare ::tncl - inehe d ep wcrr u d. On pan (1) was bright 

a nd the other (2) brown ed like t hat on the raft by pit h and . oil and b th we n ' 

pl acNl in the sun. Ob e evation. w r e made twi da.ily and the t mpcratur of 

tb ' air and wate r noted, a,<> in th ac ompany ing t}tbl . Th rat V}Lr'l <1 l' n. id •rn lly . The av mgc losR per day in the b rig ht pan wa.· 0.01 'G f n foot, whi lr 

tba.t in tb c browned pan by it. : ide for the :ame tim wa,; 0.0256 of a foot. Th 

dirt-colored pan un xpeeted ly ga,·e th hig he:;t rate of e,·aporn ti n, and tb rat 

f rom both pan xc decl that on the lake. The temp ratur , of th water in th is 

u ts wa:s n a rer that of th ai r than that in tb uve of the raft pan, a nd y t the 

('vaporation wa · . o mu h g reater on account f th hi rrher temp ratur . Tb :se 

ob ·ervation tend to inclicat that th vaporation from th la k ·an not b gr ate r 

than that mea ··ured by the pan on be raft, a nd tbi. g iv me more confid nc 111 

tb <'O n ·Ius ion con erning· the amoun t of water tha t c. cape: by filtration. 

a l,.Ourtcenth All II. Rcpt. · . .'. Weath e r Bureau, Pl. VI. 
VAPORATtoN l •'RO:M R.ATRR T.AKR. 59 

Ob. erm ti on.~ /(} determine rvawn·atim1 at Cl·atrr Lake. 

T em peratn re. -1-rr ight of water. Lo~ f w11ter. 

Date. '['im ofnl- I servation. 1 .\ ir in \Vater. 

I ha de. - Pan ·1. Pan 2. Pan 1. Pan 2. Pan 1. Pan 2. 

,., Ill~ 8. - - --- .. - - . - .. - .. . 

R ____ __ --· -·· -· . . . . 

~)_ ------- -.---

!) __ _______ ________ _ 

5.-1.'\ a .m. 

6 J. m. 

6. :iO a. 111. 

5.30p.m. 

De{!. Ji'. ])eg. F. J) g. 7•'. 

4 -10 I -10 

54 69 6 

-+0 

69 

3 

6 

HL __ ___ _____ . . . . . . . 5. 30 a.m. 3 :n 

10 .. ___ . _____ -- --- .. 6. 30 p.m. (• nn)62 66 66 

II. __________ ______ _ , 5.-!5a.nt. -1-!. -1 0 -10 

II . __ __ ___ ___ ____ ______ .do ______________ _______ _______ _ 

]:_ ___ _ __ ___ _________ ()_ 30 a. m. -+2 -12 -11 

12.---- - ----- · ------ 7.40 P- II 1 -1 3 50 ~o 

I :L . ... .... _ .. _ .... _ 5 a. n . 35 35 3 

: :!: ::::::::::::::::: . ~ .doP.- : J .... ~. _____ ~~ .... __ ~~ _ J-1. -- --- ------ ---- -- 6 P- m . 56 6 6 

In ______________ -· -- () a. I'll . -+-! 41 -10 

li) _ ____ _ ·- --- -- -- -- i Jl- m. 60 60 

ltL ...... . ... _ ....... {i. :JOH.Ill. -1,, -1 2 -+2 

:::: ::::::::::::::::: --t~--~~) ~-- ~': _ ------~~- --- -~~- -- ---~~- / 1 i ___ ___ ____ ____ . ___ . ___ tlo _ _ _ _ _ 5 :6~ ~~: ·~ 

1 

1, ___________ ___ _______ . d o _ _ _ _ _ ~ > v 

lB ... .... ...... . .... I p.m. --------

N>et. 

0. -110 

--1 00 

. :~9 0 

. :~ 0 

- 37fi 

. 365 

. 355 

(I - 3!)5 

- ;{(.-

- 372 

- 370 

-:-!60 I 

a_ -110 1 

-:390 

. 3 fi 

-370 

- ~60 

. 3:-o 

n .-100 

-:375 

. 350 

. 335 

P rt. l•'eet. Peel. 

0.-100 

. 3 0 -~--~~-- -- ~--~~-- -360 -01 -0:? 

-350 I -01 .01 

- 3-+0 -005 .01 

-:i20 

I -01 -02 

.:n5 I -0 1 -005 

"-3 0 ---- ---- ···· --- -

. 3()5 . 02 -015 

. 360 I . QO:{ . OOn 

. 3,55 . 002 . OOi\ 

- :~-+0 I -0 I - 01.'\ 

(1 _:3, 0 -------- ------ .. 

_ :~60 _ 02 . n:? 

.:H.~ 

-:20 

-82; ~ 

-2% 

" -3!l0 

-36.5 

- -1 0 

. :i15 

. OOn . Oli\ 

. 015 - 02ii 

-01 . 005 

-0 1 . 0~-) 

. 02- -02-'i 

-025 -025 

. 015 . oz.-

T tallo ofwa rin ll! day ---- -- ---- --- --- -------- ---- - -- ------------ . 21- .295 

vemg vaporation pC'r day . .. .... _ .. ______ .. _ .. _ .... __ _ .. __ . . ... _. _ _ _ _ . 0186 . 0256 

Th o d rninn.g-

,.: izr of' the Jnke. 

I 

q I nns refill d to h ight incli~tlt o. 

INFLOW OF CRATER LAKE. 

n.r :t within :.\1ount ·Mazama is v0ry Hmall n. compnrrc\ ·with the 

Tt i,; e in·um:crib d hy th o <-r t of th e rim and lim1 trd to its inMr 

slopr, with nn aren, acco rd ing to Mr. E. C. Barnard of 27.4 pmrc mil e... A th e 

u.rc·}t of th la ke, includino· Wi;;:ard I ·la nd. i · 21. 30 qunr mi le the dminao·e area 

r n ir ·ling the lake i.s 7.06 ·quf\.1'0 rnile - that i , le s than no-third of he ·iz of th 

lake i t. ·elf. Th pre nilin O' outh rly and outhwe t rly wind.' of winter, wb n tb 

precipitation is htrgc t and i. in th0 form of n >v , O'l' atl_v increases tb catchme nt 

over th normnl precipitation by drifting now ov r th - outhern rim. Jt hnng-. 
(i() 

upon t h inne r slope and fu m ish s many anllan hcs to th' htk ' d uring- ' in tC' r 

as we' ll as many small :-<tr am,; in sttllllllCr. ~· ixty thrC'C' small str 'atus we rC' dos ly 

c.·ti nratcd or 111 a ·ur d by runnino· thenr O \' t'l' a w ir a.t th' end of a trough , and it 

wa ·founcl thatduringthetim WC'W r c th r• th<yrtdd d to the lake l0.75+nrhiC' 

f e t p r second, or 929, 1±5.6 ·ubic f ct p e r cht.\·. Th at'C'fL of tb wat<' r :<urfatC' f 

thC' htke i. approximately :20..!:2 :;quare mil e,;, and th<· WfttC't' addC'd to th lakC' itt a 

day, although it .·c m::; large in t h nly O.OOj)!J~ 7/ 

foot. n.n rtmou nt whi ch is not appr 

. treams. would ra i:<<' i t:s s urfn.CC' 

iahlr . 

OUTLET OF CRATER LAKE. 

CratC' r Lake ha,: no Yi -ihl outlet. nor any oth r reachirw the . nrfacc dir ·tly 

within a few mil es. for if : u ·h we re the ·ase th wa.ter woull is:uf' with g-rC'at 

fon· on 1t count of tlw pre ·:ure. lf t he r nr outlet · at lower lev 1: th route 

to the opc nin o· mu:t h long and tor uou ., o that th fri ·tion eompl et ly o\·c rcomcs 

the pr·0ssure and a llow the \\'a.te r to i:. uc a::; from an ordinary :< prirw. 

The annua.l precipitatio n in th e rC'g ion. rough ly ftpprox imHted y an; ngo by ?llr. 

Gannett a.nd republish cl h,v i\lr. Russe ll , wa -· gi,· n a:; from GO to 70 inch " whi le' ti1C' 

annual cvnpomti o n. by thC' ·ame a.uthori y, is 40 to 50 inch s. 

\\ c may get n ., ug):rC'stion as to the prec ipitn.ti on in the region f ront the s now 

lin marked by moss on the roes. On th soutbw :<t p rtion of the rim th - : n w 

lirw rarwc:; fl'<?m 5 to :W fe t ahO \'' the ground . Th C' va riation is due to lriftino·. 

On Wizard Island an10ng the tree · th wind ba,..; mut h lcs:< fl'<:'d, and th e s n w lin e 

i: ,·haq ly markrd 1~ f t from tb <>Tou nd. Tbi,.; probably r·p pres nt: 1t fn.ir 

approximati on to the a,,, rage depth of snow. :Yiost of th precipitation is sno\\' , 

dth h thC'r j;; som rain. Th re i:; to nsider<tbl : now prop -rly in<.:luded in tb 

prec ipitation timate. hut not r epresented in th now !inC' . 

;\lea ·urcmcnt. w r e made in a 12-foot :; now bank n ar ('a,mp to d termin e th 

wate r eq ui,·a lent fo1· such a bank of ." no' . Tb a,·f'ragc f a numb r of trinls n.t 

difl'c r nt 1 vel · whi ch diffe r ed but littl0 aiJlong tbem:el es, was thn.t H7 in ·hos of 

:now .'·ie lclccl 22 in bes of water. Th :;now wa probahly m r compa ·t than 

thnt of tlr island. but it wa: not saturated with water. fo r we fail ed ntire l,v to 

get wate r f rom :; now hoi s, a:> we had don in prcviou: year ·. The f.! now was dry. 

Tweh•e f E't of :uch snow would equal about 5 inches of water, and it is he lit' \·e I 

that th a,·erage annual pre ipitation for that r egion i: near r· () than 70 inl'he><. 

The p ulia r po:;ition of th caldera on the :ummit of tb e broad range gTeatly 

in crea:; s the ·at bment of be I a: in for the winter :;torm f rom tb .. outh and 

:outbwe.'t d rift va. t quantiti of s now from the gentl outer ·lope: of th nm 

acro:s th ·re-t, to lodg in g r eat bank:; on the in: icl e. It , ecm · evident, th r<'-

fon', that much water mu ·t e. cape from th i. clo ely ln.ndlocked lak by percolfttion 

besides that whi clr I av ,_ . by cntporation. 
Ol TLET lll<' RATJm L AKK 61 

It wa,.: fo r t h purpos of o·etting-, if po ·:;iblc, an !tpproximat mrasttr tn cttl 

of th e <tmoun t thu: lo ·t by percolation that ob:c rnttion · w r • madl' last ;;ttllllliC'r 

of th e evaporation nnd infiow at the amc tim that th r sinkitw of thr htke 

surface wa:-; mea·ured. From tb. oh ·cn <ttions it <tpp an; that whilr th lak ' 

$tnk at the rate of 0.0155 foot p r day , notwitbstandi tw a :-;nmll infiu x, tit loss hy 

c ntpo ration was only O.OL .. 5 foot p r d<t ' · ln other wo rds, a n anw.un t equal to 

about one-fourth of that lost· by cntporation escape.-; by percolation tltroug lt the 

porous base of Mount Mazama. 

Tb walls of the caldera inelosirw th lak ar nt ad • up of :tit nmt ing sheet:< 

of lav<t dipping away from th' la ke pmctically in a ll d ir ctions, and a rc :o p· r o·n,.. 

as to afford asy pa ·:;age for mu ·h water. Spring . .; arc abunda.nt an d r ma rkabl 

m ·i?.c, e: p ·ially on th e . outbeast ·ide, along a fau lt which fonns a hlufi' ext nding 

from Modo0 Poin t by F or t K lamath far up dircctl.1· toward ' ra t r L ttke. 

lt .· y probabl that thi · faul t cutting th old ht1·as of ,;'VI ount Mazama, afford:< 

an outl t fo r much f th wat r tbat perc latcs thro ug h that po rtion of th mn · 

Much of th is ' pring wa t r app 1tr: to b appr·ciably warm r tb<tn that of tbc main 

hody of rater L ake. 

P RT I 

THE PI~TR0(1 H \PHY Oli, CRATER LAKE NATIONA L PARI\ 

J ) 11 H 'E B HNE J>A'TTO 

I 
, I 
CO TE~l'. OF P lRT II. 

Pngc. 

Hyp r ·tb ne-and . ites . ___ . _. __ .. . ___ _ . _. _. __ . _. ___ __ . __ ___ ... ________ . __ . __ . __ _____ _ . . _ _ _ 69 

JVlineral components __ ________ __ . _ . . __ ___ . _____ _ . . ____ .. _ .. _. _. __ .. _ .... . __ ___ ___ . . _ _ _ 69 

Plagi ocla e ___ __ ___ _______ . ___ ... __ _ . _ . . . ___ ______ . _ . . __ . _ .. _ . __ __ .. __ . ___ • __ __ . _ _ 69 

Pyroxene. _____________________ __ _ . ___ __ . __ __ . ___ . ___ . __ . _. __ _ . __ . _____ . . _. __ ____ . 7 

Hyp rsthene ________ ____ . __ . _____ ___ . ___ . ___ _ . ___ . _. __ . _____ __ . ___ ______ .... . 7 

Augite ________ _______ ___ __ . __ . _. _. ____ -. -.. . . . - --. _. ___ __ ____ _____ __ _ ..... _ .. 

A ces or ' min ra ls ___ _____ __ __ . ___ ___ .. _______ __ ___ . __ .. ___ _ . . ____ _ . __ . . . __ . _. __ . 

lassifi cation of and ite. _______ __ __ .. _____ . ___ . __ _____ __ .. . _ .... __ .. ____ . ____ __ _ . ___ _ 

H yalopilitic type . ___ .. ___ __ . . _____ . ____ . __ ___ ___ -.· . __ ____ _____ .. ___ . ___ _ . . ___ ___ _ 

Hypocrysta lline type _. ____ __ ____ _________ __ . _ . . . .. _ ... _ ........ . . . _ .. __ ......... . 

. ubtype A .... . .................. ....... .. . ........ ......... . .. . ..... . . . ... .. 

ubtype B 

H ry ta llio typ . -- -- -------- - -... __ . ... __ .. ___ . _ ...... . . _ .... _. __ _ . .. __ .... . . 

Dacitic ty1 e .. . ... . . _ ... . .. _ ... .. . .... . . _._ .. . .. _ . . __ _ . . _ .. . .. _ ..... . __ . .... . .... 91 

rn rta in ·pe --.-. -... . . . -.- . . -.. -. .. -. -. -. .. --- .-- .- ... .. -- --. -. . . . -. . -... -.. - 91 

And ;;it dik ... .. ... ... .. ... ... . .... ... .... ..... _ ..... .. . .. .......... _ .. _... . .. . . .... 92 

:\fin ral ·otni on nts ___ . ....... . ......... .. . . . . -.-- -.. -.-.--. -.- . ....... -- . .. -. -... .. . 

F ld par ... ___ . _ . _ ... __ . _ . . ___ . __ .. _ .. ___ .... .. .. . _ . .. . _ ... __ .. _ . _ . .. .... __ .... . . 

I l orn bl nd _ . _ . ... _ .... . .... ... . ... ... _ . .... . _. _ . . . . _ . _. _ . _ . __ . .. . _ ... _. _ . ___ __ .. 

H yp r. th en .. .. .. ... ... .... .. . ... ..... . . . _ . .. . ............ _ . ..... _ ........ . .... . 

ugite . _ .. _ .. .. -.- ------- -. . -- --.- .. . . -.. . -- . . . . --- -- · · · · · · · -· · · · - · - · ·- -· ·- · · · · - · 

Oth r·min ra l.- ....... . ...... .. .... ... ... .. ... .. ............ ........ ... . . ... . . .. .. . 

Di tril>uti n a nd d c:rirtion nfda ·i t rna e.· -· · -····-·· · -···· ···· · ·· · ····· ····-·· --- · · 

Llao Ro k fi ow ... _ .. _ . __ . ___ __ .. _ ...... . . . _ . _ . _ . _ . ___ . ... _ .... _ .. .. __ _ . _ .. _ ... , .. 

\ itrophyric dacite ........ . ... .. _ ... . . _ .... ..... ....... -.... . . .... ----- ... - .. -

Lith ida! dacit _. _ ... .. ...... ... . ___ .. . ..... . . .. -. -.. ........ .. - - ---- ---.--- . . 

. 'phe rnlitic dacit.e .. _ .. . ... . .............. .. .. ....... -... . -.. -.. : .. .......... -. 

ndular ecr · tions . . . . _ .. . . . . . . _ . . __ ...... . .. ... . ......... .. . . . . .. ... -. . ... . . . 

G rou. e Hill flow_._ . ___ . . . __ .. . __ . __ .. __ .. .. .. . _ ... . . _._ .............. -. .. -..... -. 

94 

95 

99 

100 

100 

102 

10-! 

104 

104 

105 

105 

105 

106 

107 

109 

111 

112 

\Vinegla fl w. _.: __ . _. __ . .. . _ .. ___ . __ . __ ___ _ ... . ... .. . ___ . ___ . __ .. . .. . ..... ·.. .. .. 113 

lou l np fiow .. . _ .... _ . . . _. _ ... __ .. _. _. ___ . __ . . .. _ .... __ . ______ . _ .. _. . . . . .. .. . ... 1.14· 

Sun r·eek fl w ___ __ ... _ . . _ . __ . . _ ... ..... ... . . ......... . _ .. __ . _ .. __ ___ . __ _ . _ ...... _ 116 

9255·- ro. 3-0 --:) 65 
0 TE NT OF PA HT lT. 

H rst ci te."-Conti nued . 

Dacite tuff .. _ .. . _. _._ . .. .. .. . __ . ___ . __ . __ .. ___ __ _ . ___ ... __ . __ - ___ __ . -. -. _ . . -. ..... .. -. 

Dacite dikes .. ___ _____ .. __ . __ . . . __ __ .. .. __ _ . . . _--· -.. .. . _ .. --- ..... --. .. -.- -. . ....... . 

Dacitic ejectamenta _______ _ . . ...... .... ... ... .. _ ... . ........ . ......... . .. . .. . .... .. . . . 

Pumice .... . . .. ........ . . .. . . . . . . . . .. . . . . .. . ... . ... . .. . .... . . . . ... .. ... . .. ... . . . . . 

Dark-colored ecretion .. .. . . . .. ... ..... .. . . .. . ... _ ..... . . . . . ...... . ... _ .... . . . . . . . . 

Light-colored granophyrir ecreti n: .. . . . .... . . . _ ...... ... __ : . .. ... ... . . . .. .... -. . . . 

ecretion_ with ba alt-like tructur . _ .. . ......... _. __ . .... . .. . _ ...... . ....... . .. . . 

Chemical analy e · __ ....... ... . __ ___ _ .. . _ . ... .. . . _ . . .. __ . __ . _ ... _ . . . . __ . ..... . ___ . _ .. . 

~ .. . . . __ .... _ .. .. . . --- · . . ____ ... __ .. . _. __ .. __ . . .. .. . . ........ . __ .. . ... . .. . ... . _ . .. __ 

Interstitia l basaltl _ . .. . _____ . . __ .. _ .. . ....... _ . .. . .. ... _ . . . .. . . ...... -.. . .. . . .. . ..... --

lin ral com ponents . . . . . . __ .. __ . ....... . ..... __ . __ _ . .... . .. . ......... _ ......... .. . 

Feld par· ____ ___ __ ___ .... . ... . . . __ ...... __ . .. ___ . . _ . __ .. _ . . . . . _ .. _ . . _ . __ .. . .. . 

Augite __ . . _. __ _ . __ _ . .. . .. . .. . .. .. . . . .. . . . . ..... . . . ..... --- --. ------ .. -.-- ----

H ypersthene _. _ . . _____ _ . . __ _ . ... _ . ... . __ .... _ .. _. ___ _ . . :-. __ .. _ ... .. . . _. ___ . . . 

Olivine . __ . .. _ .... . .. _. ___ .. .. . ___ . ___ _ . . ........... .. . . ... ___ .. . .. _ . . _ ..... .. 

YJagnetitc __ ... . _____ . . _ ... ... . ..... . . ... ... .. ... . . . . . . . .. .. ............ ---.-. 

Hyper thene, apatite, and pseurlobrooki te crysta l .. .. . .. . __ .. _. _ ......... _ . . __ . . . __ 

Apati te __ . .. __ .. _. __ . _____ ... ___ .. . . .... ..... . . ... . .. . . . . . . . .... -- . .. .. -.... . 

H ypersthene __ . _ . _ . __ .. .... _ ... . _. _ . ... .. . ...... . ..... .. ...... _ . .. __ _ . __ . _ . __ 

P eudobrooki t _. ___ .. . __ . _ .. __ .. ___ . _____ . _ .... __ ·_. ___ . _ .. _ .... __ .......... .. 

Fluidal-inter"tit.ial «a s. _. ___ . _: _. ___ . _ . . .. _ . . ___ _ . __ ............ _. _. ___ . _. ___ __ _ 

Porpbyri tic-in ter_titial ~ _ . ....... .... ... _ . . .. _ . .... _ .. . . _ ....... .. ...... . .. _. 

·.nde itic basalts. ___ __ . . __ ____ __ . . . __ _ ._ .. . .... . _. _. ___ . .. . . _ . .. . _ . . .. . ___ . .... __ . __ . _ 

Typ A .... . ... . . .. ..... . .... . .. . ....... . .......... . ... . ..... .. .. . . .. . . . . ..... .. . . 

Type B . . ... . _. __ . . . _ .. ___ . _ .... __ _ . . . __ __ . . . . .. ___ __ . . .. . ... -·-·. _ . .. . . _. _ . . __ __ _ 

Type ·----- ----· -- ·-· - -· ·- · · -·-· -· --· · · ·--. ·- · ··- -· -.... .. . . -·- ·- --· · -- - --· -·-· .. 

Typ D . ... .. .... . .. . ........ . .. . . ... . .. .. . . . .. . ..... . .. .. . .. .. . . . . .. .. · · - -···· · - -

Chemica l analyse · ___ .. . __ . _ . . _ .. __ .. . __ . ___ _ . . . ____ . ... _. _. _. __ . .. . _. ___ . . _. __ . . ... . . 

Con ·luding r mark · on th e basalt 

rage. 

121 

121 

~ 

2~ 

1 :_;) 

130 

13\l 

140 

1-l1 

Hl 

142 

14:2 

14 :~ 

H :3 

l ·H 

145 

1-!5 

H 6 

146 

1-ti 

14 , 

15:2 

156 

157 

15 

159 

159 

161 

162 

Table of thin section , wi th new and old numbers ... .. .. . . . . __ .. . _ ... ___ . ... .... ... . _. ___ . .. 164 
ILL 'TR TIO NS IN PART II. 

Png . 

PLATE XIV. Cry t.als in andesite, da ite, and basalt. .. _....... . . .... .... . .. .......... ........ 76 

.,..rv· . Thin ction of an de ite .. .. . ........... . .... . .. .. .. .... .. . . .. ..... ... .... .... 80 

XVI. Thin ction of mineral in ande it . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

x ni. Thin ction of e r tions in dacit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

XYUl. Thin ection of e cretion in dacite.. .. ... .. . .. . .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 

XIX. Thin ection of basalt and of secretion in dacite . . ........ . . . . ... ........ .. .. . . 138 

67 

THE PETROGR \PHY OF RATER LAKE NATIONAL PARK. 

By HoRACE B J:INELL PATTO r. 

HYPER 'l 'HENE-ANDE ITES. 

Th ande ite · are the Ide t of tb ,·olcanic rod of rater Lake and form 

the g reat bulk of the xpo - d rockH. Tb y are all hyper tb n I earing, and may 

tber fore be cla -ifi d a · hy p rsth n ·and ite-. But in ·pite of the fact that th y 

may all b plac d und r tbi on· b A.d there i n, r markabl div r ·it · in thrir 

xtemal app aran e, inasmuch a · th ey vary in color from bla k to li g ht o-ray or Ji o-bt 

drab and in textur from vitrophy ric to holocrrt.-'Lllin . 'I'hi di~· r ity of t xtur 

and color i onfin d, bow v r t th groundma ' · that i · to ft.)', the pheno ry.:;t;;, 

a lth ouo-h th .Y ma) ho~ mfl.oy and ntried di tinction , do not app ar to b d peodnt in their variati n · up n th cham t r of th g roundma · · to any very great 

ext nt. In th followino- d ' Cription f th e r o ks th ph nocry t. will b fir t 

n ider d, a they ur in all th and itic' mri etie 

b de ·ri b d in ('Onne tion with th di u. 'ion of th 

d pend ntir ly on th 'ariations of the oToundma' "· 

MINERAL COMPONENTS. 

whil e tb groundma' will 

differ ent mrietie - which 

Th pheno ry. ·u of the- r ck · ar ba i · vla io Ia byp r then , auo-it , 

and mao-netite. Tb Ia t-named mineral , to b sure. doe · not app ar a a pheno· 

r ·tin th hand ·pecim n, but it i alw ~ pre nt and h long·s in part to th ry::;-

tal li zabon of th fir t g-eneration. T the above hould be , added olivine and 

homblend >, whi h ar v r · eldom pr ·ent. 

PLAGJOCLA E. 

A a phenocryst plR.gio Ia. e o ur · u ually 10 ' tout cry tal with barply 

develop d face and rath r numerous cry tal form , uch a · ha,·e be n r peatedly 

de crib d a · chara teri··tic of ande ·ites in o-eneral. Th roo 't promin >ntly developed 

form i u ually the brachypinacoid (010), the habit of the cry ·tal being- thick·tabular 

parallel to this form. The n xt mo t prominent form i the ba ·al pioaooid (001), in 

69 
70 PF.l'R GRAPHY OF RATER L.AKF. ' ATI AL PARK. 

addition to whi h rna · usually be found a macr dome, probably (1 1), and th two 

partial prism (110) and (110). Thi habit cau. en e tions pRrall 1 to th bra hypinacoid to have hexa ·ona l haJJe and :ection ut perp ndicular to thi · face to have 

v r.v oft.en r ctanguJrtr or fiv - or ·ix- ·ided . hap .-. Th plagio las cry tal u' ually 

mea ur 1 or 2 millimeter in Jong-est diameter. At mo>: t t ho dimen ion r aeh 3 or 

±,but not infr quentl.r a re on id r,tbly le · than 1 millim r. Th y ar nea rly 

alway: abundant, but ma ro opically are con picu us nly in ca e of thr dn.rk-· 

colored pecimens with g-la 5 gr undma . (2, 3, 17). ln the han l ·peeim n th e 

plagiocla ·e · are nearly alway perf ctly fr h ftnd gla y. Th y can not r n.dily be 

di -tinguish ed from ·anidi ne, owing to apparent ab nee f cl avage and twinninotriation ·. 

In a few case twinning· appear to be entir ly ab nt, venin thin s ction><, but 

u ·ually the cu -ternary albitic twinning i very pronoun d. Thi may be dev loped 

in a few broad band · or in many thin one that may or may not xtend a ro · the 

ry tal. Not infrequently twinnino· triation · at right angle. to the fir t and produced by the application of the peri ·line law of twinning ar to be s n. 'ry tals 

thu twinned may be till fu rther complicated by th pr ence of twinning after th 

Carlsbad l::~ w. 

Maximum extinction ano-les mea. ured to th right and to the left of the tra 

of tb albitic twinning plane on . tion cut at rio·ht an o·le to th hrachypina oid 

indi ·ate in almost ev t·y a that th se plagiocla.'e ph nocrys ' ar \·ery ba i and 

ar to b - ·las d a anorthite. Out of n. laro- numb r of such m a ur m ntl:l the 

f !lowing may be g iven a indicating fairly a' erao-e re ult . fn ea h a e the 

angl given i · the large t that wa · noticed in th e pecim n refe rred to. 

Jfaximum extinctiOrt angles of plagioclase. 

No. 41. . . .. ............ . . .... . .. . .............. . ....................... . .... . ... . 24° 

Nos. 9, -!:3 .. . ... . ............ .. ... . . .•.•••••.•.••••.••..............••....... . •• 26° 

No. 44 .. ................... . ..... . ..... . ...... ....... .... . ...... .. .... . . ..... .. . 27° 

No. 65 . . .. . ... . ... ..... . . . .... ....•............. . . . .•.. .. ... . .... ... ....... . . . . 2 o 

Xo . 11, 24, 31, 35 . . . . . .... .. ... ... ................... .. ...... .. ... . ... ..... .. . . .. 30° 

No. 66 .. .. . .. .. . ... ... . .... . . . . •.. ........ . .. . . ..... .... .. . ... ........ ......... . 31° 

X s. 2, ..... ... . .. ... . . .. ... .... ......... . . .. ... . ... . ........ .... . .. ....... . . . .. 33° 

l 0.'. 3, 42 .... . .. .. . . .. . . .. .. . .. . .. .......... . .. . . . . . ... ... . ...... ... .. ...... . ... . 35° 

No. 79 .......... .. ... .. ... ....... . . ... . ...... . ... . . .. . . ..... . ..... . ..... . .. . .... . 38° 

It ii> not to be inferred from the abov that the mall r number of d g ree n ce ·arily g ive· the aetual maximum xtinction, ina much a. it i no always po.·sibl 

to find a cry tal cut o a to o-ive ·uch angle:. 

Almo t in variab ly these phenocry ·t how a weU-developed zonal -tructur . 

Thi. i v ry mu h more marked in · ction parallel to the brachypina oid than 

in those cut p rpeodieular to that face. Th general rule m uch ca es seem 
ANDE 'ITE . . 71 

to b old tru her al..:;o. nn.m l.v. that th extin tion a rwle · ncar tb marg-in of a, 

cr y tal arc 1 s than near th center. [n No. '7\:l th cr rt;.tl who·· cxtincti n 

ang·l i;-; g i,·e n abov a. 3 ° fo r a . ection cut a t rigb aoo·le · to tb bm h,rpinn -

coid o·a ,·e at the margin an extinction ang l of onl y 30° . Thi: diff r n f 

eig ht. d g r ee ·· for uch ·ecti n:>. while pe rbapl; not rnr , i;-; larger than ordinary. 

In ver y ma ny a e. the d iffer ence 1n ·u ·h ·c ion.- 1. not mn.rked. Tb 

diff l' nt extinction :-:one. som tim :- g radua.ll,r ·hade into L' a('h oth r: som times, 

howev r, the tran ition i' Rhrupt, o r r latively o. ot infrequently n. narro> 

marg in will show a, notedly .·mall r extincti on angl than do ,; thL' rest of th e 

ry ta l. In ' till othe r ca"e.· the erystal may be di,·ided into ,. ry irreo·uhu 

. patch ' that .· bo w itb r nndulous xtinction 01· : 1n cwha t diflerent appearingzonal banding in tb diffe r nt part:. _\ r cul'l'ence o r alt rnat i n >f hand that 

show r e p ctivel)7 g r eater ancl . ma.ll er :din tion ang le. · in th same cr y. tal i b. 

no mean rar . 

A i cu tomari I th e ase in an d e. itic ro k ·. the e pla.gio<.:la pbenocry: ' are 

oft n haract ri7.ed by indo ·ural;. The. o· las,.: ;.l ug it . hyper. the n magnetit and apatite. as well a.- oth er not w 11 -c baracte rized suh.' t.-'u1 c s. \Vith th e 

ex ception of g la · the:;' inclosed ub:;ta n ·e.' a r only oe ·asiona lly met ·1\'ith , and tlwn 

any on r u1 o r r C\' n all of tbern may be se n in tb r same l'r.v ·tal. Eve n o·la. R, 

whi ·h is RO ftn n cham teri,-ti · f ,Lnd .- iti 1 lagio ·la.-c i,.; by no 111 an,.: always 

pr ,:;c nt. In ·omc ·a .. uon of the plagi o la · l he no ·ry t ' e ntain ,; ut h inclosur s: 

in otb r H' CR s nw ph cn c ry,:; nmy · nta.in non whil , otb r:; may b fill d or 

p erhap:- ontain o nl_v ~catte l' d in I : ur '. These o·las: ind ·ure a r usually Yery 

irregu lar in form , but hey ma. ' a. I so b ·imply sph eri cal or ova 1 o r 1 olygo nal. In 

•olo r they are:.; rn etim ·· a I a.r de p brown a.nd ar cith r a.b:; lut ly f r o from any 

ery;-;tal!in 111fltt I' (17), 0 1' el.•t> in incl o ·urcs of the oa,m brown color tb r c rn:w b e 

s e n mi ·r liti c i nc lu:-; ion · f au o·it and mao·n tite, exactly the ame as arc to b 

foun] in ·lo, ed in th brown g la ' ba ·c of tb g r undma · (Hi. 6). or. ao·aio a 

minntc aa:; bubbl (6 ~6, 17). ' u b g 11 · hubhl .' a.r a.pparcn ly mu •h more apt to 

o cnr in b row n g las inclosur s in th e plag·io la,:;e pfr n cry:'l than in tb colorl ': 

g-In: in lo ·ures r f n ed to be low. Brown o·la ·s incl o.- ur ' ar con fin d mainl.v to 

t ho e and ite. t hat h!l\'e an abu nchwt brown o·la 'Y ba · and that b lorw to tb 

h_v ldopilitic type. Bu t x ceptions t this rul e ha,-e h e n not d (42) ' he re a -omewba.tl a.l r gla.:.- c urs inclo · din p lag i Ia pbe n ry.ts that are mbedd din a. 

hypo ry tallin e g roundma ·: in wb i b llttle or no g la ·s ba a n be r eadily identified. 

In tbit> ca' it i.-of iot r e -t to not that a pale-lrown o·IR · of the -am olor a that 

of the in lo. ed o·la>~ .' a nd practically fr from I)Ii crolitic or tbe r ry b o ·cur in 

mor or le i olated nr a · forrn d b_,. the rn -tino· of ' veral pbeno('l'yst of plagiolase or of otb r min raJ . Browu g las · inclosure occur n arly alway · i ·olated or 
72 l'ETRO ,RAPRY OF RA'l'ER LAKE ' A'l'IO L J'Al K. 

·parino·ly . catter ed thr ough th ·ry:tal and no onspituont'ly parallel to the outlin es of th ph no ry t. There ar , ho\\' \' r. a few cases wb er this br \ n gla 

tbi ld)· Towd.· th cry:'tal or a pftrt of it oro cur ' in a zon int rn1 odiatc hetw n a 

cl ar · nter and a clea r maro-in. exactly ~lnn oo· u · to \\'bat i. dC' ·crib d llPlow a. 

more charact risti0 of. th colorl ess gln ·s in losur s in f ld par. 

Colo rle- alas · in lo:ure. of \·ery il'l' gular shape and fair ·izo thickly r wdin..,· 

tho mass of th e feld ·par a to leave tho latt r in n. . ort of sk leton form ar by no 

moa1 s rare. hut th y ran n t be . aid to b 'O cha.ractcri ti a::; arc >< imilar o •urren ·e that will b de cribed in conn · tion with th · daoit rat r Lak . 

ually olorl e: gla ·s in ·lusions ar \' ry minut in ·i"' and ar d n ly r wd d 

together . o a.· to gi\-o the £ ld:' par a loud d appeamnc . " ncb o·la.·: in lu ion 

boYvev r, arC' almo ·t n vor f re from ·ry tall in matter but ontain mor or l . 

w 11-d fined material ·imilar to that , een in th groundma ' · f tb hypocr.\" ta llio 

and ·ito. . Owirw to tbi. cry tallin matt r of th g las in ·lusi t1'' th e f ld ' pars ar c 

rend red not only cloudy Lut appear di rty a. though fin rn ry clu .. t had b n 

ground into them. The very minut g la .· in I Ll i n · arc not ahay. fr ' h. but 

may contain at time. ill-defin d doub ly refracting cl ornpo.- ition ma.tter. The di:-

tribution of th se be louditw gla. s in elu ·ions is xtr m ly vari d. 'om times th y 

fill the whol e of tb · cry ta l i11a . . alth ough th . nearly alway,.; I av a lear out t' 

maro·in. A otb r time tb ar n.ggregat d in the c ntml part of th ry tal, 

whil e till again they may oc ur in an inte rmediate ~on e, le.-'wing both th e center and 

th margin Lear. In th la t ea;:; this loud ed :.\One may I r, th er broad a nd no 

harply defin ed either toward the <"e nter o r t \\Rrd th maro·in or it may 1 narrow 

and tb n more harply delimited . 1 n gon ntl the outer dg of tbi ' zon i: apt to 

h mor ]early defined than i th inner edge. 

Th ~;e thi kl) crowd c1 g la · ino]osur :are n t to h found .in all tb · plagiocla 

pbonocr)7 ts f the am thin section, nor ven in all the ph nocr . ts of the ame 

g neral habit. metim · th y ar to b n in only two or thr whil be 

1·est are ntirely fre from uch inclo ure ·. Tb ir occulT nee e n to be, r . ome 

.· rt of r Jationsh ip to the character of the oToundma:, , more parti ·ularly to th 

amount of the g la · pre nt in the g roundmass. A: will app ar later, th and sit 

of 'rate r Lake will be treated under veral bead , ba · d upon the nature of the 

g r undma. . Of tbe ' e ther are thre main typ s. nam ly: 1, Tho with holocry. taJiine groundma · 2, tho e with h) pocry tallin groundma ·; 3, tho with 

h aJopilitic 0 TOundma ·. Th Ia ·t-named type ontain an abundan e of brown 

o·h1 . , th ·econd con ·id rabl , but not o evidently clevcl.opod glas ·, and th fir ·t no 

g la · at all. The r lation hip of the e deo:e inclo. ure to the amount of g la may 

be indi ated by th e fo llowing compari on, which is confined to those phenocry ·ts 

that how well-characterized inolo ure of thickly crowded o-la with a lear margin 
A DE I'l'E . 73 

of feld par outside : Out of ixteen thin ~· ction.· of n.nde ite with holocry tallin 

groundma s, only two, or 12t p r cent, contain . ucb inclo ure ·· out of tw nty-on 

ections of the hypo !'l:ystallin typ , eleven, or 52t pe r n , ontain uch in lo ur · 

and out of twenty-one e tion · of tb hyalopilitic type, thirt en, or G2 per cent, ontain plagiocla e of thi · de ·cription . It '"'ould e m, the refor that th pr once of 

gla · · in th groundmu.s. ha :om thing to do with th rowdin0 · of cm tai 1~ of tb 

feld ·par with gla. inc-lusion . It hou ld furth r b . tat d that plagio la e ry ·tal ' 

that have ·uffered partial r e orption, ·o a · to appear in mor r 1 ronnd d form 

have a . tronger tend ncy to cont.-'1i n such rowded o·la ·. i ncl n ·ions ban ha e tho 

cry tal · that do not . how ·uch r orpti n. It should a! o b t.-<tt d that th ahov 

compan on do not take into account th very ab undant but larg r and mor 

i olated, in lusions that d not have a mark d t nden y to occur in an in tcrmediat 

zone. o uch la> ·eems to appl_y to u ·h inclu ion . . Th mineral inclosure in ph'to·iocla ·ear not often ver) a.bundant. Mag neti 

occur in the cu tomary mall octa hedron or in grain and apatit in . harp n edl 

or ·lend r pri m . ug ite a.nd h_vper:th ne ar u ually to b se n in roundi h 

grains that hav the . arne color and gen ral appearance a wh n not in ·lo ed. t 

times the re i · to be ' en a sli ·htly oT eni h fin ely and irr o·ularly granular min raJ 

as o iatcd with th gla.· · in lu ion , that app ar to r · mbl augit more than any 

other min raJ unl ·s it b pidote; but tb gr at fr shn · · of th l' rock would 

em to xclud th last-nam d min ral. notber in lo d mineral, that occur 

in r undi b or oval form and ba · a li o·htly ' llowi b olor 'vitb ratb r trong 

r fracti\'c pow r , mav b zircon, but no barpl formed cry tal of zircon w re 

noted. 

R rption ph nomena arc v ry ommon 1n connection with th ·e plao·iocla 

phenocry They ar se n in th e rounding of the corn r: or in tbc f urth r eating 

into th f Id ·par · o a. to e~v th m in roun d g rai n · or in tb fo rm of embayment . 

u h orrod d f ldspar cry tal ~ tat d ah ve ar p uliarl y lia bl to be fliled 

with o-la s in lu ·ion. to ' uch an extent that there e m to be but a. keleton of 

feld par filled with gla . Th ' <'O tT ded c ry ·tal almost invariably b ' a clear 

maro·in of later oTowtb. Th formation of an int rrn diatc zon of g la · inclu ion 

i · a.l ·o v ry tr ngly dm· loped. and in thi · ca c th outline of th e loud d zone are 

cl arly parallel to th oute r c lg of th e newly extend d ·r.r tal, xc pt wh re, 

occa ·ionally, tb lear margin ba d v lop u new cry ·tal fac s. In di cu ing thi 

well-known ph nomenon Prof sor Ro enbusch ays:a· 

" Evidently a p riod of re orption of the already crystalliz d feld pars is followed by one of rapid addition of n w feld par nbstance, during which the gla · 

inclo ure \vhir h are tak n up in g reat quantit on ac oun t of the rapid growth 
74 PETROGRAPHY OF CRATER LAKE TIO AL PARK. 

mu t arrange thems lve parall I to the d formed p riph ry. Then urn a p riod 

of slow growth, with the con qu nt fr ·edom from int rpo 'itione', and the ffort t 

produce r egular cry tallo phi c r estoration ." 

This explanation .i plau ·ibl and i · po ' ·ibly tr ngth ned hy th fact }1bov 

noted- that the d velopment of thi · int rrnediRte zone seem. in . orne way depend nt 

on the amount of gla s pres nt in tb groun !mas ·. It w ul d s m that th p ri d 

of r orption wa. follow d, in ca. e of th ' C andesites that ha17 e develor ed a bolocry stallin e grou ndma ·s, by a period of slow ·ooling, whi eh wa. not fa ,·oruhl o th 

in orporation of numerous glas inclusions :tnd which conti nu d 1 ra ti('ally unint rrupt d until th 1vhole rock b rame ·olidifi d. t)ti ll it doc:; not s 0111 cl ar ju~t. why 

t.hi ph nomenon fl hould be depend nt on th e pr ent condition of th g roun dma · · 

for both th0 bolocry tallin and th partially o·la . . y g roundma ';.;e mu. t hav b n 

fluid during the p riod of r orptio n whi ch i.· common t both. noth r fatt often 

ob erved in . tudying thee ro k: does not s em t fit in with Prof s or Rosc nbu h · 

explanation. It i · tbi. : That tb inner line of th e intermE>diat zon iR notalway. 

a · harp a' i· th out r on . In fa t, it may b quit in g ular and not sharply 

defined, a: it ·hould b . In ·uch cases it mor clo ·ely r ern blr: tb g radua l 

encroachment of fLiteration prod uct upon <"1. clear and unalt r d int ri r. , 'uch 

feld par cry ' tal have the app aranc of having b n honeycom l cl i 11 the pro ·c•ss 

of re' Orption, the pore. tbu:; produced b ing fill ed with th Slll'l'Oitnding [''lass. 

uch a bon yeombing . if p sl'ibl e. wou ld n t n ce a ril.v advan into thr int rio r 

of the crystn,l qually in all dir ction · nor 1 ave alway · a perfrctl.v : harp line of 

epa ration. 

Th above-mentioned oh · · inclo-ures in plagiocla phenocr,v t." a. w 11 a.' some 

of tb re orption ph nom oa and sub · quent new g rowth . a re brough out in figs. 

A, B 0, and D of Pl. XIV (pag 76) and in the photom icrograph pr nted a 

figs. A, B , an l D of Pl. XV (pag 0). Fig . A, B , , and J) of Pl. XIV illu. trate 

th d i tribution of gla in lusioo · imila r to the O'roundma:::s: al · the clear margins 

of later growth, free from : uch inclusion: . Tbe g las in clu ion: are rend r d bla ·k 

and often opaqu through includ d magn tic du. t. 

In addition to tb plagiocla.' cry tal.· alr ady de:cri b d, ther i very often pr -

ent a pbenocry ti c p]a0'10 Ia ·e that occurs in long to short r ·tangular :ection · with 

quare, diagonally exting ui bing eros· ·ection. Th are crystal elon O'ated parallel 

to th e cry tallographi axi , and similar, ther efore, to the mir roliti · plag-iocla e · of 

th e groundma · of andesite. and ba ·al ' , In mo. t ca··e they ar entir ly eli tin t 

from the groundmass plagiocla e, as well a from tb above-de:cribed I henocry t . 

They ometim · form tb only plagiocla e pbeno ry t pre ·ent, but at oth r tim 

they occur togeth er with the fir t-described kind and form a econd O'en ration of 

phenocry ts. Thi type of plagioclase i · characten. tic of the lava· of Wizard 
.. 

PLATE XIV 

75" 
PL TE XIV. 

CRY TALS IN ANDESI'l'.E , DACITE AND BA ALT. 

FIG . A.- Plagiocla e in hyalopiJitic ande ite fr m and r k. Ma<mifi d 30 diamet 1 . p cimen No. 5. The glass inc:lu ion are mainl y confined to a narrow zon n ar th e margin. H as unde rgone partial re orption and econdary enlarg ment. 

:FJG . B.- Plagioclase in byalopilitic a.nde ite from Anna re k. l'lfagnifi d 60 diam te1 . • 'p imen Q. 10. Glas: inclu. ion a re unif rmly li tributed in rath r hug and iYTe<>ular patch Ha 

undergone re orption and . light econda ry enlarg m nt. 

:FIG. C.-Plagioclase in hyp cry talline a11desit from water' dg und er Llao R k. Magnified 

60 diameters. peci~:h n o. 31. Gla iuclu ion u.niformly and thi kly eli tributed throughout tb 

original cry tal. Ha · m1d rgone secondary enlargement without r orption. 

:FIG. D.- Plag iocla. in hypocry talline ande ite from Grotto OYe. :.\Jagnifi d 30 d iam tm 

pecimen No. 55. Gla inclu ions uniformly and thickl y eli tributed, riginal cry tal part ly re or bed, 

and a econdary enlaraement pronounced. 

Fw. E.- And e ite at water'. edge west of Ea<> le ov . Magnified 60 diamet r . • 1 cimen ro. 

11. bow a pbenocry t of augit uJTound d in part.by a rim of parall I growina hypersthene. e 

page 2. 

F•o. F.-A plagioclas ph no ry t. Fr m th vitrophyrir dacite f Llao R ck. ::\Iagni ti d 60 

diam ters. p cimen Xo. 102. Polarized light with ~ d nicols. . how · distin t zonal structure 

and two dir ctions of cleavage, the basal parallel to t h mall face n ar to the fi"ur 3 and t h pri -

matic parallel to the long t ide. The ection i · cut nearly para]! 1 to th brachy pinacoid. The 

interm diate bell 2 is more basic than i t he cente r. e page 101. 

FIG. G.-A minute f ld par crystal containing a large inclo ur of brown gla. with outlin 

parallel to tbe.sid of the crystal. F rom the vitropbyricdacite of Llao Rock. Magnified 400 d iam rs. 

pecimen o. 101. Tbi glas inclusion ontain a ·ingle ga b ubble which II] pears like a b road black 

ring. ee pag 106. 

Fro. H.-Corroded hornblende ry tal with re orption rim f augite and magnetite. :From the 

dacite of Grou e Hill. Magnified 200 diameters. p cim n No. 10-. ee paa 111. 

Fro . I, J, K.-Crystals found in the cavities of basalt from the base of Red Cone, o. 156. Figs. 

I and J are hype1 thene and fig. K is pseudobrookite. pa<>e 146 to 14 . 

Fw. L.-Oli\'ine phenocry t. From the basa lt of De ·ert one. Ma<> nifi ed 65 diameter.. pecimen o. 169. Alteration product is like that of fig. If, but alteration is not so far advanced. ontains 

a plagioclase crystal projecting into the. ide. ee page 153. 

Fw. M.-An olivine pbenocry t almost completely altered to an opaque mass of which magnetite 

appear to form the bulk. :From the ba...<:alt on the inside of the crater of Red Cone. :.\Jagnified 110 

diameters. pecimen o. 174. ee page 155. 

76 
U. S. GEO~OGIC L SURVEY PROFESbiOr.AL PAPE.A ~0. 3 PL Xl\1' 

a m b 

(I } 

CRY STALS IN ANDESITE, DACITE ' AND BASALT. 

A DE ITE . 77 

I ·land (19 20, 25 30 9:'). b ut i: not confin ed to that locality. In No. 21, from 

entin el H.o- k this t rpe of feld pari · repr ::>e nted, one crj :ta.l of whi<.:b wa notined 

cuttirw ·l arly through a ·ma ll hyper ·th ne ph noer. t. A · b) pectbcn i on uf 

the old t ingr eli nt: in th e ande ite , this would indi ate that the e plao·io lase 

rystal · can not be con:id red a · part of th g- roundma ·. Thi: i xceptional , 

howe\ r, a~ in mo '· ca ·o:- th plao-io la e i- eli tinctly younger than hj persth n . 

Th y do not rtppear to be much le ba ic if at all, than th plao-iocla e of th fir. t 

o· n ration (20 g ive. maximum extinction ang l on ' e ·tion. p rpendi.oular to th 

brachypina oid of 30° and 33°). They arc u. nally f ree or nearly free from in luion but they may cont.-'tin gla s inclu··ions and ev n be crowded with tb ame. 

F rom th above it appear. that, taking into ·onsideration the plao-iocla of th 

g roundma . . thi' mineral occu r' in many of. tho 'rat r Lake ande ite in thre 

di tin t gen ration . Th two generation among th ph nocr.r t ar u ually quit 

. harply d fin d and r adil,r. r cogn ized, but thi i not qually tru a· b tw en the 

e ond o· neration a nd th third or that o curring in th e oToundma -. The e two 

a re apt to ·bade into ea ·h otb r. In c 'rtain in tan ·es it i' m re t han po ·ib l that 

till another a n ration may be pre. ent. Thr g neration of plagiocla. ar 

brought ou in fig. D of Pl. XV, which abo illu:'trate. a more or I . pronoun ·eel 

tran ·ition b two n th plagioclase of. the gro un rna :-~ and that of th ond 

o· ne ration. In th i::; ca tb groundma ... - f ld ·par, are mo tly too small to b 

' r ad ily eli c rnibl e in th illustration. 

Th plao·iocla · of. the oToun drna' mri o-r atly in ize and habit in ac ordance 

' ith th degro of '1')' tallizati n. 1 n th mor gla · .r and ite it i \' r apt to 

a. um di tinetly rni Tolitic fo rm, o that th microlitic lath may not mea ur more 

than 0.005 rnillim ter in d iameter; but mor· cu tomarily they ar onsiderably 

large r than thi and d \' I 1 lono· and ·hort lath forms that g radually pas in to th 

. maller ph n cr.'' !'.:', so that a di tin ction b twe n the two i · not always a ·ily mftde . 

. ually the plagiocla ·o lath .. -ho,·v xtin ·tion ang-1 that ar n tv r y mu h maller 

than tho ·e of be phen crys . For in ·tan o, on rock that ·how: ymmetri ·al 

extinction ano·lc: of 2 ° and 3 ° among th I beno .- ~ contain g rou ndmas lath: 

with xti n<"tions of A 0 , 26° , and 270. Th polysy ntheti twinning- i, n t alway · 

el i ting uishl:th lc, b nt whcr <' th i.· i,.: appa.r ntly ab ·cnt an undnlou xtinctioo is very 

l·.ommon. In c rta.in of th holoc rystn.llin ande ·ito · two geo ration · of feld:par nr 

to b s en in th oTo undrnas:-;- first .. an old r, lath- hap d ,·ari ty with dev loped 

twinning ,.;tri< and oco nd, an ineo· ulftrly doYoloped r e ·idua l f ld ·par that u ually 

do · not l:ihow tw·inning, hut which ha. ;tn undnlou·· extin tion. Thi · la t-nam d 

vari y i::; commonl. 111 irrco·ular a ll otriomorphi c patches of con ·id rabl . ize, 

. how . .,; simulta n on.- or· n Gtrly : imu lta.n ow; oxtin ·tion , ftnd in ·lo e~ th other win -

m ls of th g round111 a. s, uch a p lagiocla lath · augit' , and magnetito. This 
7 PR'l'ROGRAPHY OF RATER LAKE NA'l'IO AL PARK. 

re idual f ld:>par wi ll be more fully consicl ered in connection with th d ription 

of the bolocry ta llin ande 'it s. An xcc ll nt cxampl o. 73. 

PYROXENE. 

Both ortborbomuic and monoclini · pyroxene.· ar bam t ri tic ingr di nts 

among the pbenocr) t-, the form r heing byp r tb n and th la,tt r augite. Tb ,. 

two min eral. ar nearly alway abundant but ar ne\·er l.arg cnouo·h to b om 

prominent in the band ;;p imen. In ,.; n ral, tb yare hotb of about th am ·ize 

ometime one and ometin1 tb tber being the larger. Tb y n,r not often 

O\ er 1 millimeter and n v r mor than 2 millimeters in oTe~tt t diam t r and from 

tbi tb y may ink t mic ro ·copi · dimen ·ion ·. In the band ::sp im n th y an not 

b d istingui bed from eal'h other. Thej hav n, greeni b t brown and browni bgreen color and di ·tincUy r ·inou appearance. Th ) a t: p rf tly fr b and break 

without apparent leavage in roughly oncboidal fractur . !though fr qu ntl. 

bun b d together, o a to app ar large r than they r eally ar th y r equire a magnifying g la to be lead een. lthouo·h both of th ·e pyrox ne · ar a lmo. t }tl.way 

present, they vary g reatly in their r elative abundanc . For in tnn , in a .·eri · of 

ix , p cimen' · collected along the path de cendioo· from th amp oTound to the 

water'. le \ el- a vertical di. tanc of about 00 fe t- w bav hyper ·thene th<' more 

abundant in o . , 9, and 24, while th rev rse hold · for No . 7 42, and 4-1:. ln 

gen ral howev r, hyper thene i- tb more abundant (2), although it may b come 

-care (16). Augit on the oth r hand , i::; rare!) mor abundant than hy per -thene, 

and i · often either ('.ar ce (40) or ven aJmo ·t completely wanting, o a to b repreented by only one or two roundi h grain in a thin ection (30, 56). 

H Yl'}:JlSTilENE. 

The hyper. thene phenocry u uall y occur in well-d veloped cry tal tbatapp ar 

111 hort to long pri -matic habit, . eldom in ,·er · .·lend r pri ·matic habit. Th form N 

nearly alway pre ent are the brachypina oid and mac ropinaco idH (1 0) (010), and 

the pri m (110). The pinacoid · are equall develop d and nearly alway ar more 

prominent than the pri m. Thi giv . to the cro. · . ection eith er a quari h form 

with truTl'Cated corn r or an octagonal f rm. The terminal face · are not , ea ·ily 

d t rminecl, but the appear to b a flat pyramid or eq ually flat dome. ·. In som 

ca ·e tbi. mineral may occur in more or le . irregular gTain ·. Thi.· i not apt to be 

the ase when it oc ur:; i ·olated, but it oc ur. in thi manner when it form , ne ts, 

either alone or ,.,ith augite and magnetite (2). sually the hyper. thene i · o lder 

than augit , but at times th two app a r t have been formed ·imultaneou ·ly. 

In not very thin sectio ns hyper thene appears ;;trorwly pleo ·hroic, and i then 

distinctly g r eenish parallel to the vertica.l axi · and reddish or browni h r ed at rig ht 
. , 

.. 

PLATE XV 

• 

79 
P LA '.rE XV. 

THY:'< ECTION 0 1!' ANDE ITE. 

Fro. A.- Ande·ite from th e south rim of the caldera. Magnified 94 d iameter ·. Sp cimen No. 1. 

A photomicrograph in wh ite ligh t. how·· a pla"ioclas of th fit t gen ration wi th the c nter 

extremely pongiform and crowded with brown gla.;. . Th tructur thus develop <.l bear a el o e 

r emblance to the in tergrowth of feld par and " lass in the light-col r cl <> ranophyric . ecr tion 

among the dacitic ejectamenta. S pa<> 132. 

FIG. B.-A.nd ite of th hyalopilitic type from t of and r ek. lV[agnifi d 20 diameters. 

p ·i men No.1-. A photomicr •raph in white li"'ht. how plagioda e ·ry. ~ f t wo well -rl fin d 

type . In the center i a phenocry:·t of the old t generation with clear maP in and clear c nter, 

corroded an one ·ide, and ·howin"' an interm d iate zone of brown glass inclusion ·. F r d cription 

ee page 74 an l -L 

FIG. '.-Ande ite from the ri m outh of The Watchman. Magnified 6 diameter:. • pe ·imen 

No. 60. A photomi ·rograph in wh ite light. , hows a ·rysta l of h yper then ontaining small incloures of glas, wi th a bu bble in ea ·b in closur('. T,,.o of th e may be ·e n abo,· the c nter a nd to 

the ri" ht and left of the two con._picuou;; clca,·age cr·a k•. . e page l . 

Frc . D.- Hyalopilitic ande ·ite from the water·'s ectg we t of Eagle Cove. ~Iag nifi d 20 liamet rs. 

'p cim n -o. 11. A photomicr graph in white light. Th . cti n illu. tntte tb ~ o ·currence of 

pla<>ioclase in thre g ne at . Fir t, the olcle t, la rg 1 heno rysts wi th g la: in lusion , in thi 

ca ·e near t be margin; second, phenocry t: wi thout a: ~ inclusion a nd that haYe mo tly r ('ta.ngular 

form. ; thh·d, small lath. of th gronndmas feld ·par that a rfl m tly too small t be c n: 1 i ·uous in 

the photograph. e page Ti. 

80 
U. S. GEOLOG CAL SURVEY 

(D) 

NDE ITE . 1 

ang-1 .· to thi: axi,.;. The:; ~· ock:,; a rc .·o lin grained thrtt they r quir rathe r thin 

:e tions s that the hypcrsth no: : how much pal er colors; hut even in th ' ve ry thinno ·t :e ·tion: one ·an r cognize t h distincti,· pi 'ochroism, a ra) s ,·ibrating parall I 

to th vertical rtxi: arc a lway: g r cnish, whi l tho. e vibrating at ri O' h ano· le to tb 

\'C' rti ·rd ax1 · ar e faintly redd i.·h or yellowi b. The thr c ela -ticity axe agrc with 

th thr cr tal axc ·, a:;fo( low,; : a=·t,b= lr c=.c. In onvcrg-cnt light ·cction,.;cut 

at rig ht an o·lc · to th e vertical a.x i · g ive lL positive bisectrix a nd large optiral a ng le, 

whil e :cction: ut para llel to tb mac ropinacoid g i TO a negativ hi ·ectrix and ft much 

,;ma ll r optic,Ll a ngle. I n long-itudimtl :cction::; the pamll l eav~ gc line' ar u. uall.) 

well develop d, a · i:; also a ·ro 's fmctur , I ut th cu tomary pri. mati and pinacoidal 

c.: l avagc: ar not often sharply de(in d in horizontal :cctions unlo. · tb ·ection is 

unu:ually thin or the c rysta ls laro·or than common. 

:\lin ra l inc! ·ur s in hn or;;th n are con fined to mag nctit and apatite the 

f nn r b ing ver y common a nd the lnttcr rar . G la ·s in lu, ions, how ver, are v ry 

common and cbaracteristi ·. They ar e almo.' t alway · to be ·con in th larger and 

sometime: also in the ,·cry ::> lllftlle." t rystals and mr.r ~n number from on to 

twenty or mor e in ca::;c be ·r." tali:-; unu:ually larg . They arc u ually round i ·h or 

ontl , but may he irregular in ::; hap , or t b y may have pol.\' O'O na l forms r mbling 

that f th cry ·tal. They ar e usually co lorl cs: or have rt light-brow n bad , but 

ncY r tho d cp b r wn to be . c n in man · of tb f ld ·pa r,:;. Tb olor of tbcs 

o·las · inclu ·ion.· d s not so m to d pend on the 1 r of th o·]a,.;s 1 rl ·c nor ev n upon 

th pr s ne of such ba . .:\ cnrly a lway ·· each of th ·- in ·losur · may b een to 

ontain <L gas bubbl . the iz of whi ·h do : not b ·tr an~' r la,tion ·hip to the size of 

the indo:ing J las::>. H we \· r , one C<tn oft n find gla ·s in ~· ure::> without ga 

bul blcs in th' snm cry -tal in whi ch most of thC' g la : in<..:lu ·ion · contftin bubble . 

Tb s1z . of : ucb in clusions Yari c: from about 0.01 tnillimeter to very minute 

mi croscopi · dim n:i om;. ln fi g. of Pl. XV i · pres nt d a h} l crsth n c r\ tal 

with s 11 b inclo ·ure: of o· lasf' and bubbles. 

H Tpc r:th n is a lmo ·t in va riabJ.'~ pcd eetly fr ,.; h. l t ma,r at tim · .· how a lig ht 

tmt of scrp ntinization through the lev I pm nt of <L y llow ish, ·fi brou ·, p olarhing substan ·c. 

,• stat('d aho ,·o, h,vpc rsth no i · to be ran k d a::> one of the oldc,' t cry:tallization 

but a lt houg h it oe<.:a ·ionally o ·cur::> in clo.·cd in th 1lao·i cla ·e pbcnocry t · it is not 

a lways oldC'r than thi · min era l, a: th p lagio ·Ia ·c somctim · impre · ::> it · fo rm on 

the hn ('r.-tbon . 

In add iti on to ph nocry t.-;, not a few of th Crat r Lake andesite: al o contain 

v ry much small er hyper. then ry ta ~ 'v itb a lend -r la.tb -lilc habit. It i not 

always clear wb cth r th e c rtr e to be considered as helono·ing to a late r g ncration 

and a: form ing a, part of th g rounclm<t ;· or not. In a few ·a e , at len ·t, of decided 

925. - No.: - 02- G 
2 PETlW(;Il{ l'HY OF RA'l'ER LAKE ATIO fAL PA I{K. 

gla. ·y vn.ri ti · (9, l:i, 16), this concl u ion ee :-~ to be ju. tified. ln :-~ u ·h rock th e 

g roundmn. ~ on. i s of a brown o·la s eo ntaining lll}tgn titc grai n., a f w f ldspM 

mi c rolite: , a nd al>u nd}tnt .~ nd r a lmost rni roli ic prism · of n.ugit a nd hy p 'r:;thc nc. 

The hy p r,;tlw n is q ui t , uniforml.v abou t 0. 5 millim te r in le ngth a nd }Luout onefifth to one-te nth of thn.t amount in width. The ~wg t : ar' sorn t illl cs ht- sa n1 

,; i;~, c, b ut ul':lually not more tb:Ln ha.lf a,; hu·g ' · Th :; ' h,vp r:th n s of the g ro und -

lila :-~ a rc . harp, a nd tb y frcq u ntly . how thtt terminations. They conta in nnto·n titc 

}tnd nJ·o g la · inclu: ion:; with hubbies. Th y arc tno::; tly ,·c r,r d isti n ·t from the 

byp r tbe ne of tb tit· t o· ncration in i;~, ' and ba.bit n.nd ar very much mo re 

abundant. 

.\ UC 11'E. 

The phcnocrysti c augit a r , like th e hypc t" thc ncs. usually sharp ly ·ry ta"lli~cd, 

but they ar not :o p r.'i t ntly idiomorphic. Th y no infrequently o · ·ur in 

hyp idiomorphi or in oTa nul a r fo rm:. This, of cour ·c, i : naturall.\ the ·a c where 

t hey fo rm c. t · e it he r svitb or w ithout bypc rsth nc. ln c l r tb y : how in thin 

. ctiom; a near! · unifortn pale green, the d pth of color ,·arying with the t hi ·knc-,s 

of th . lido. They rar' ly .·bow a ny itppr ciahle pleocb roi rn and t hi: p rop rty 

to ·ether with the .•tronO' r inter£ r enee colors and tb obliqu xtin ·tion, nea r!.'· 

always :uffice. to d i: tingui,.,b them from t he hyper thc nes. TwinninD" p~tnd l to th e 

o rth opi nacoid i · very common . This i. tru not onl y of . implc tw in , but al,.;o of 

c ry ·tal: with r p eatcd o r polysynth ti · b\ in nino·. 

The inclosure: in aug ite arc exactly the .·arne- ven to tb e g lass in ·lu ~ with 

buhble ·-a. ar to 1 c found in hyper t hcne. Th ·ry tal form i al ·o '' ry do e ly 

amdog u · to t hat of th orthorhombic pyrox ne. Th .' are tbe prism with hm ·h.\'-

pina oid ~ and mac ropinacoid. n.nd a tlat t ' rmimd form, prc:umabl,r n p ramid. 

·ually ho,vever th e pri ·m a nd the pinacoid: ar about qually dcv lop d. 

Parall l growth:> of auO'it and byp r: tb nc ar occa ·ionally to b ' ' Cll (ll171) 

in whi h th auD"ite fo rm. mor or le ·. itT D"u lar ·b ll · a round t he old r bype r. t he ne 

( ·ee fig. g of Pl. Xl V, p. 7G) : b ut t bi:> phenome non i' by no mea n.· a · common u 

with tb basalts of thi: reg·ion. A more dek'tiled d . ·ri1 tion will b found unde r 

th ba ·alts. 

A: a g rou ndma: R co nstituent augite i. ,. r y characteri tic and i · uui ,· r:;ally 

pr :P.nt. In 1roportion to the cl ve lopme nt of bypocrystalline grou nd nt a,.,,.., thi: 

min cml i · to h . ce n in mor and mor granular form. ln th e g reat Jn ajo rity of 

s pec imen . . however th i,.; mineral a m11 :well-defin ed .: lender pri:,;matic form. ln 

t he hya lopili ti va ri eti e. th form i ' 'e ry shftrp indeed. Th r y. ta'l mea:ur two 

or tbre o r e \·e n five t ime.-; aR lono· a. widr. fn rxceptional ca ·e, tbe length may ho 

proportionn.te ly c~Lt r :till . ( 1 ·un.l ly in ,.; hfLI'pl y dcvelopPcl c rystn.llit : th width 

vari : b tween . OOJ. ~t d 0. 00± Ill i 11 int tc r :Lnd th ' 1 ngth he twce n 0. 01 and 0. 03 
A DE ITE . 3 

millimeter. In the holo -r ·talline ntri tic. th auo·ites arc not only g rnn nlar tn 

shape, but u ·ually much larger. Both mi croliti c and granular indi,·iduals ·u. toma rily inclo.·e minute ntagnetite in octa,h dral and granu lar form ·. 

ACCP.: ' 'Ol{Y 1\IL'Il!:JtALS. 

Quartz do ;; not app . ar to form a.n :;:entia! itwrcd icnt in the~ and . ito:. C'X • pt 

a: it may form part of the all otriomorphi c c:o or c.-~ lllftterial to be ,;oen in most of 

th bolo ·ry talline vari ti c.·. \Vi tb thi.· ex<:cption thi:s mineral ha"' been <·rt'ta.inly 

identified in onl y tw·o a ·c: (-16. 7H), and in the:P two l:<'lSc. it do · not o · ' til' at all 

evenly distributed hut only in a few itT g ular grain: ti.Jat mfL.)' ea ily J a· ·ount d 

for by secondary o r ac id n~d cau ·c:. 

Tridyn it ' wa: r e ogni7.ed in on ly one ·a: . an <tnde. it of <l de cided ly dacitit· 

ty pe (79), about H miles s utlt of the catHI g round . 

Hmnblende.-A ve ry f w y >llowi:b -hrown and strongly pl och roi · eryl'tals of 

this mineral mo::;tly in fragm nt..-, a r to be s en in :pccim n l'iio. +±, from ncar t he 

camp ground, and :pccimen No. -:1:5, from Cftth dral Rock. Th larger g mins ha,·c 

the b la ·k r e:orption rim of magn titc. o common in andesites. ln ti.J ·maile r individual · th r . orption i compl t a nd only a black 11m. ;; of g-ranular magn tit 

r mai ns (sec Pl. X I, B). I o on : mall crystal i · ,;' n in No. ·+' a roc·k nw ·tti ona l between ;tnd ito and dacit<'. Tbi · min mi. \\'hieh is \' Cl',Y ommon in th 

da ·it s of "rate r Lak , i::> otbcn i · ntir ly wantitw in the and it ::; . 

Otirln ' o<: ·urs ,·ery ·paritwly a an oeca ·ional r ound d grain or fra rment, 

II tore pftrticuhtrly am JW' th n ' t::; of old r cry ta.llized mineraL-. ] n near! · all th ' 

a nd :its it i: ntircly wantino·. l t i: mo ·t abundant in t\o. -I:!J, wh re it is se n in 

well -rounded gntin: tbat ba Vl' marked rc ·orption rim: of magnetit a nd ap1 arentl,r. 

of augite. Jn o. -t3 ther arc one or two fo rm · wbi ·h rescmbl oli ,·in ery::>~ · 

an l which arc till d with a, y ell wish p larizing ·ubstanee, pre: urnably . crpcntin . 

"Jfagnetite form · an always pre ' ent but r atb r sparingly de,· loped ing red ient 

among the min ml.· of tb fir t generation and oceur:· frequ ntly inclo ed in 

plagiocla e, hyp r.-thC'n and augit . In the oToundmass it i · perhaps more abundant, 

a nd th n oc ·urs as ::;mall oetah dral ry:~d ;:, or a::> grains; al. ·o in the a ndesit s with 

a brown gla::y ba::>e, a: a,. r.Y fin ' powd r. It i::> likewi:c Yer y abundan t a indo urc: 

in th augite microlite: of th ' gr unclmass. 

lfel!latite app ars to oc ·ur o ·casionally either as a r ddi ·lr .;tai n ur a..- minut 

bruwoi b-r ed hexagonal . cal · (6-). 

CLASS! FICA TION OF ANDESITES. 

"While tb r pheno ·ry t." Huctuate g reatly in abun lan ce ~nd 1· lati,··e importance, 

they do not IT as w lJ a · doe th g roundma · · a,.· a ready mea ns fo r da ifying 
'4 PETROGRAL'HY o~· HATE!~ LAKE NATIONAL l'AJ K. 

the wid ly diffe r nt app a ring vari ti :of tb and 'Hi tic roek: . ' rtai n ·t ructu ral 

type:-; in the g roundm;l:: on the othe r b;tnd, r ·u r with g r at frcq uen y and n re 

worthy of detail ed d ~< ·ription. Tb • an le..; ite::; of Cm.tc r Lakr, thc r fore , llHIJ h 

d i,·icl cd in to four main tyr c:, ba::;cd upon th ·Intra ·tcr f tht uTou ndmass, namely, 

h,v<llopiliti c type : hypo ·ry::;tallin c typr, with two subtype: (A and u); ho lo ·r,v ·-

tall inc typ ; daciti tj pc. 

Although each of tb s four typ ::; i:; qu it di::;tin<.:ti,·c , it i · not to lw ""PL>O:cd 

tha.t all the xamplcs cit d in caeh ca:;l' arc cqwdly so. H.n.th r it may be "aid that 

th y all oTad into ea,ch othe r in :u ·h <t way a: to ma ke th 

ca ·y. Neither can the ro<: k · of an · on lant "tr am or of 

lituited t any one type. 

H YALO.J>ILITI TY.J>J~ OF XDJ': l.TE ~ 

s para ion not alwa ·: 

nc locality h ·aid to b 

The fo ll owing sr cim n · arc indudcd here: . l , :Z 3, -1:. 5, 6. i, . 9,1 11. 

12, 13, H, 15 16, 17, 1 ' 19, 20. a nd 21. 

Thi:-; vari ty of andesite ha · ma inly a very da rk-gra _,, to b lrt ·k, d n ·r g roundma.s . . and wh en it i: not por ous i::; apt to br akin : mooth ,;li g htly lustrous surfa ce ·. 

The . pecimcns tha t co ntain 1 .-.· g la ·s, a: w II a th more l or ou · on ·, ha,· a much 

lighte r color a nd roug her fracture. On account of th d~t rk oTo uncl ma ·: th 

plagioc la. e phenoc r.n .;t ar c u. ua1ly prominrnt. and for th : nmr r :t ·o n thr pyroxnc· a re hard ly noticca.hl . :\lost of the h,r a lop iliti c a nd .- it .. <tr chara ·tc riz d in 

thin :; ction: by the Il' once of lio·bt to l ep br own glass which i: us ually v ry 

abundant a nd perfectly c1 ar and unalte red (6, H. 11, 13 16, 17), or else thi · brown 

gla ·: i mo r o r les. e1oud d b.)' th pr : n ·e of ·oun tl ,': bo ·ts of minute b rown -

to bla ·k-lookino- g lobuli t s (b rown in ,', 15, 19 1, ~; 1 lack in 1-l:, 21). T n ca: th s 

g lobu1ite: a r thieker than usual, th g la::;s base I etwccn th mi c ro litc. hcc- me,· 

lig hter o r even almo:t ·olo rl e ·s: but : till the efl et of th g lobulit ::; in su ·h cas ,.; i::; 

to lenQ a browni h c lor to th e whol . In a few <'a c · a d ·ide l cban o- of eolor in 

tb gla:: is to b not cl , in tha.t b la ·kish . pot:> a.pp. <tr lo a lly in a g la. s othcrwi: 

hrowni:h (12 "'0). The: bla ·k . pot..; w the cd obulitc very thick and :om wh at 

larger , while th .in ·losing o·Jas: ba · 1 · l'Oiorl s. lt is more than like ly that 

mag nctit d ust is d ,. loped in addition to tb c customary o·lobu1it ::;, which wo uld 

explain th hla ·k color. Thcs dark r : pot-; ar si111ilar to th whole g roundma ·.- in 

·ome f th hypocry tall.ine andesites. 

This a li-p n ·ad i ng- g1a · · ba ·e i 11\'ariably i nclo: , · tnyriads o f pe rf ctly sharp and 

·traight augit mi c ro litc ; also plag ioela.-c fe par~'! in ::; lend r ::; trip.· of mi ·rolitic 

'izc or in hlro-cr laths and in r ecta.ngular individual: . The l'l il'. of the augite 

mi crolite · may vary co n ·idr rably in th e am c thin sectio n. Thus in o. 2, wh rc 

t hry arc un commo nly : mall , th ey vary f rom O.OO L to 0.00:) tnillimC' tC' r in ·width :wei 

from O.O L to o.o;) rnillim te r in length. [n g ' nc rul the width may be ::;a id to 
ANDY. TT'F:R. 5 

ave rage about 0.005 mil lim te r. with extrem · of t\.001 a nd <UJL millimete- r, a nd the 

length to a 1·era.ge a ho u 0.0:3 millimeter. w ith xt .~ of O.Ol ;tnd 0.08 millimete r. 

lt will b seen that they nrc :tbout fi1·e to te n tim 's ;ts long ;t;; wide. T he ·e mi crolite. a re very commonly free h om irw lo ure . hut 1 r ba.p: more fr q uentl.1· in lo::;e 

minute magnetit oTains, or octahedral nysta l · of the ;;am . The plagioclase 

mi ·ro lit ;:; and la th - vary ex r mely in si11e and fo rm. In the majority of en;; ,; their 

fo rm i: e ithe r d i.-tinctly mi ·roli t ic or, at lea.· t, :;lende r lath Hhaped and minntc 

~, 1±). \Vh n ver y mall the cu::;tomary twinning is not fll'l il y d i. tirlO'ui. hab l , but 

in t he larger a nd broade r i ndi viduals po l,v:.vnthetic tw inning is ;;tr ng ly in C' l7idc nc . 

Inte rsper ·ed wi th t hese elende r p lagiocla. ·e::; arc oth r" wi th ::;hor t, r ctangular fo rm." 

that :ornetime. sho>v twinning and ·ometim ::; do not. fn a fe ll' ro ks tb s r ctang ular fo rms fl.re very num ron::;, a nd partially r fLlmo. t eomp let ly :;uppln.nt the la th 

fo rm (11 19, 21). ' t ill large r p lagio •lase;; of rectang ular fo rm co nnect thcs 

r et.c'Lng ulfl.r p lagio ·Ia ·es of the g roun d rna,; · wi th the p h noery. ti:i. ·o tha t a sha rp 

disc rimi nation i · n t fl lway::; po::; ·ible. F luidal a n ang mcnt of all tb se g roun drn;h;s 

ing r cl ient'> is mor e or I s conspicuou: i n all th in sections. 

Intermediate ·tagcs between ;tndc:;itP;; of t hi.- type and the next ;tr I'Pr.l' 

common. a nd a r mo ·tly in cluded in those list d und r the fo ll ow ing typP. ln on 

·p t imcn, howrv r, No. 1 ", ·o.llected about on rn iiC' ~o thw ;;t of the ha.·c f Hrct 

' 11 , w ha1·e what i · C'Ommon . nam ly. a tran><ition to tb holo rysta ll in ty p . 

I n the t hi n . cction from thi r ek th r e :tppcars to b very li tt l~ o·la_ .. ,., b ut t he 

ap1 P:tranc· of du::;t-like ,,;lohuli tic mate rifll between the ahnndant fcld ·pars of the 

oTourr clma:;:-; ind ica t .- th prt> 'Cn · of mo r g la.'s tha n ~ at :fir -t apr 1ll'e rr t. 

IJY I' RY TALLINE TYPE OJ:' A Ti)'E TTE. 

Th i: may fa irly be :aid to he th norma l typ of ' rater L ake an de ·ite. ; at lea;;;t 

it is mo re abundanti · rep ro ·en ted than a ny tbe r. It may he d ivided into two 

:;ubtypc;;, ' hi h, th uo·h uni ted by num rou onn ecting link;; arr upo n th ;whole 

reftcl i ly d i:ti no·nishcd. l n th hand :;pccirnen, how 1·er t hi,; distinction between th 

two ;;nhtypes <·rw not be nHtd<' . Neither c1tn t he two b r ad ily st in g- ui cd f rorn 

the bynlopili tit type ex('ept in thin :;ection. Taken as a whol!', t b y a.re dcc idedlv 

dn.rk-col red r ockil with ;l basn lt i(' look, but the darke r vari ctie: di ·ting ni ' h thems·lv · hy th r lati1r promin ence of the plagiocht:,;c phcno ·r_v "ts. :K ot a few are a:; 

dark as th darke:;t f th hyalopi li tie a nde:>it -:;, but they lack tbc g lo ., y lu ter 

·ommon to some of that t) pc. Th :w rage co lo r i naturally lig hter thfln in th 

hyalopilitic type, as tb y arc mo re decided ly c ry:;talline. In fact. not a f w in cluded 

unde r both of tho two subtyp s ha1· ;t o·ray or even a lig ht gm · or dmb colo r 

break wi th r oug h fm ctur , a rr d approach to th holocry.· ta llinc a nde ites. Th 

py roxene ·, a:; usua l ftl' inconspicuou: and have a ·ligh t ly re ·inou:s lu tf'r w ith g r ee n 

to brown ·olo r:;. 
.PE'I'H OO HAPHY OF R ATRR LAKl•: .r A1'10 AL PAHK. 

II Y.PO HYH'I'.\ LLINI!: A~l) ).: l'I'E, Sl H'I'YPI•: ;\. 

Thi.- variety inclndC';; tlw follo win·)· sp c: ime n.· : Los. 22, 23, M 2:' . 26, '.t7, 2r:l. 2!! 

:)0. 31. 32, 33. 

Th gro un nHt ~s of tlwsc I''> ·k,.; <ts s •en nnde r .t he mino · ·op ', i · v ' ry d 11 .·e. 

It i · ro\vd d with mi croli t ic c·t·ysta lliz<ttion. im.ilar to hut mor A.b nnda nt thA.n 

tho;;c in th hyalopiliti · g roun d tn t.;.,; . (:;.la:-<s is prol n.bly always pr se nt, impn'gnating the w ho le, but. with on or two exc·cptions (:20. 2<'), it is not <tt a ll eo ~p tt s. 

In the two ex t ption=', whil'h arc• rocks nn cding t hi,.; typl' with tlw pre ·eding-, the 

la ~s is r ea.di ly r eog ni z<tb lc <tnd h<t" a d i;;tin ct brow n t'olor· t h rwisc the g la,.;s ha;.:e 

appeM:-; to be rtlmost colorl <'s,.;. .\.,.; stated above. in discu:-;si ng thr plaO" iocla.-: 

ph cnocry:-;t:, t he:-;c rock:-;. with a snm.ll amount of colorlr,.;,.; u·la,;,.; hast'. a r \'<' !'.\'apt. 

to c·o nta in clear b rown la,.~: inclo 'Lll'Cs in th plag io ·la.':lc . Tlw mnrkcd frat urc of 

t hi: s ubtype A, ns ]i ·t ing uisbin O' it frotn . ul>typ H i::; th pr s nc·c of innnme rahle 

minutr p hLg io ·la.-e mir roli tc:-; with tb ir ·ustomary tluidal a.rmng ment. Th ·e 

mi c roli ti · plag .iocla · n.rc m stly ve ry minut , b ing often no larg r than th fLL!O'i te 

mi eroli tc:-; (2G). Th lrL rg r. :quarish or ·hort-r tangulnr p lag·ioc h1s<' -rystals. with 

fL nd without t winning ;;tri;-e that a.r to lw 'C'(' n commo nl y in thP g roundma ·s of th 

preceding ty pe, are usually co n,pic uow; ly nb;;e nt. H e nce th contra;;l lwtwc•r n 

the p lag iochtse · of ~· g r oun dma:-;s ~t l of t h0 plwn oc rysts i.- I' P- 1'.\' pronoun c·Nl. as 

·onn t'<;ting· type;.: a rr ahsrnt. fn o nr or two spPC'i llt <' l1 :-< thr app<'amnc· e of fai nt ly 

drwcloi rei nllotriomo rph i feldspar (:2'1 . ~!-l ) c·on n(•d,; th i;; type \\' ith thn holonysta llin e nn lcsitcs. 

In the fin c:t-gnt irwd \·a ri ct iE's tit plag ioe lasl' mi croli trs a rc hardly d iscc rnihk 

in white li g ht. In such rocks the g round111ass prese nts a cl irty-h rown or u·myil:l bhrown itnd mi nutely granular app a rance, O\\'ing to th deYe lopmc nt of thil'kly 

c ro wded augit micro! it s, whi ch arc> in te r:pcr ·eel with minute grain: and o tahedral cry ·tal · of magnetit . Tb b rown c·o lor is d ubtle.·: d m in pnrt to the 

o·la s ba ·e and in p art nlso to th pr e nr<' of b rownish g lohulites. (-Tlobuliti · 

fo rm: are, how ver, by no means rLs ·ommon o r nbun dant as in t he hyal opiliti C\ 

type. On th othe r band , hoth mag netite and aug ite in mi cr oliti · fo rm arP much 

tll Ol' <tbundant in this type of andesite. Th r nugit mi c roliLe · are, as ~t g neml 

t hing , not as sharply e ry tallized. a lthoug h they do not cl ifte r g r eatly i n size from 

the simil ar mi ·ro li t : in t he hyal piliti c a ndc.-itc·;;. As the g r ound nHtss bceollt(' 

more di. ti nctl.1· crys t~tllin e th e siz of the ·e mi cr olitrs t nd.- to heeomr l<trgcr and 

the fo rlll le ·s sharp. 

A few cry ·ta ls of <ipatitr of a hrowni h olor meas uring 0.1 millimeter in I nO"tb 

a ud 0.015 millime te r in width were noticed . Thr y ar fa in tly p leochro ic with the 

·u. tomary ab ·o rptio n E > O . 

Hype r. t henc in two gE> ner ation:- one in ;.:hort, sto ut, ftnd r elativ ly la rge cry -
A DR TTR • 7 

tal , the other in lend r pn. m of mueb .·mailer . i7. - are u na,ll.\ to he ' en, but 

the distinction I tw en th t"·o ilj not a.· well d>fin ed aR 1s the ca. e m ntion d 

in the by alopiliti typ . 

In all but on e ca e (33) th C' e ande ·ite. appear to be ver y fre h, th a lt rations being hard ly more than iron tain . Tn be one ca:s ref IT d to th e gT undma .. ba ' under gon e con. id rable alteration whi ·h ba1:1 attacked mainly tb o·h1s" 

ba. e and the aug-ite mi crolit s. Th decompo. ition prod ue:tt rtre cnrhonfltE's nncl 

a nenrly homoo· neou, oT eni b ··ub ~'t cc whi ch. in pola,ri7.C'd li D'ht, app0a,r" to ])(' 

formed of ex tr em ly Lninutc :cale that polari11e ligh t . trong·ly. rl'his g r en substan e appear to b dele ·site. 

The g roundma of ubtype A corTe pond ly to what Ro" nluseh calls 

the pilotaxitic t.VP of ande ites, in that it may be dE'. ·ribecl ns n d0ns0 ly f ltPd 

n.ggregate of p lag ioclru c a nd a ugite mi crolite · impr g nated to a 111 or or less 

extent with an inc n::;pi non. g-la ' bn . 

Thi ·vari ety of hy po r . !K'Lllinc ande.' it is r epre ·e nted by tb foll owing· :-p .cimens: No . 3±, 35, 36,37 , 39 40. 4:1 +2, ±3, +±, 4: , 4:6, :1:7 4: , ±9, 50, 51, 51?, 53, 5+ 

55 . 56, 57, a nd 5 . 1t i a more abunda,nt type, th C' r f re, than i · sul typ A. As 

above .-t.ated, the:e n.nd it do not differ mate rially in the hand spec imen from th e 

:-; ubty p just d snibed. l nd r the mi op the chi f eli tinctibn li es in th ompa rati vr suppr s. ion of the di -tinctlv microliti I lagiocla. e nnd in the oTeater 

abundan · of tb la rg ,rand broa.d r f ld par that a.r e not alway:; to be sharply di ,_ 

ting ui b d from tb ph nocry. ti · pla.gio Ia e . In this nbtyp t b rock a,l o i.-

trongly in lin cl to d Y lop a,Jlot.ri omorpbi · feld ' par , and in tbi.· way , a:; well as in 

thr de velopment of mor nn d mor· lath- bar ed a nd broad 1· ctanguJar- baped f ld-

. pn,r , to pa into tb holotr} . tall in ande iter<. 

Tho p im n tba,t ar tran siti onal to subtype A (40, 43, 47 ±9, 53 54) ha\' l' 

plag io Ia e lath v r.Y a.bunrlnntly de,· lop ·d, b nt the a.re u unll~ · ·o mu h largP r 

tha n tl1 mi 'rolitic f ld ·par;:; above de cri b d that th y may hardly h le ·ig nated a:-; 

mi crolit . . t the ame time th aug ite mi rolit becom l:lrg r a.nd lose th ir 

:;ba.rp outlin a nd o·la -. is hardly di tin o·ui ba.bl . Other pecimen tra.u itional to 

th bol o ry tallin and itcs of tb third tn e, ·bow th d v Jopment of a 'mall 

amount f allotriomorphi · plag io Ja e or quartz a nd cont.ain a g reat a,mount of th 

r t.angular feld par form · (5 , 52). It '' en ha,ppen., tba.t both th e.· tend n ie,; an' 

manifest in th e ·arne ro I (5±), o that num rou · mall plag iocla. e lath.· in fluidal 

a.rra1wement oc m· with a rather va()'u pa.-t of allotriomorphic ma,te rial. 

The mor normal m mb r · of tbi · typ , although uhj cct to co nsiderable vnriation in SlZe and r elative abundan c of th e component mineral ·, a well a · in tl~ ir 
PE'l'ROGRAPHY Ol<' CRATER LAKE TJ AL P RK. 

·tructural arrangement, may be n.id to ·ontain num rou. · p~ no ·ry ·ts of hyp r. thrn 

and augite and ·pecia.ll ·of plno·ioelase, embedd d in a. hyponystallin , or at mo.'t 

very fin ely cry -talline grou ndma ·s of plagio ln.· , <HIO'ite, and mag n tite, ' ith probably a little hardly <.listingu i ·ba.bl e ·olorl e' .' g-la.· · ba · . The g las. ba::;' 111(t}' be 1 r -

. umed to be pre ·ent on a count of th pr sen c of n li tl browni.·h lobuli tic matt r 

in the inter tice.· between th fe ld pnr::;. Th augite of the g roundma ·: rar ly has ,ts 

. harp form -, and is a.l. o rarely as :ma ll n. in th two aJrca<.ly described tn In a 

number of th thin ·ection::; :;tudi d i ha · <t o·mnulnr o r rouo·hly pri mati oTanubr 

habit. The sha rpne · of outlin e ·e m::; to eli ·a1 p a r almo:;t r gularly with th 

in a. ino·. iz of the grain of the g roundmas . The 1 lagio la ' of the groundrm 

i. the mo. t fluctuating inoTedient both as to amount and a: to size and habit. In 

. ome th e slender htth-form, in other the . hort-r 0ctangular habit pT dominate:. Tb 

color of the groundma.::; i in roo t ca ~ · lighte r than in subtyp A, o'ving to tb e 

grea.ter coar en :: of grain and to th car cit of o·]a · . These ande ite · C \" 11 more 

than tho e just described pos ·e: the trongly felted structur characten tic f the 

so-called pilotaxiti g roundmas. of Ro.-enbu ·ch. 

Mr. Diller ha briefl y d ribcd a bype1·. thene-and ite from tb later lava. of 

Mount Sha:ta, in California,rc that i:· almo t identica l with everal of th ' rater Lake 

andesites included in :;ubtype B. 'Ih r e. emblan e xt nd both to the g roundn1a 

and to the pheno ry ts of plagiocla ·e, hyp rsth n and a.ugit . I wou ld, in fa t, 

b impo::ible to t 11 from the thin c tion alone fr om whi ch of the two vol anic 

area · thi ro ·k cam . Thi: and . ite :from "Mount ba:;ta i · o. 7 of tbe Educational eri e · of Ro k pecimen · c llected and eli tributcd hy the Unit •d tat 

Geological urv y, a nd was olle ·ted at Hor · Uamp near the timber lin upon the 

we ·tern : lope of the mountain. 

Anothe r well-known hyp rsthene-ande ito tha r·e ·emble · t hi. typo a far a · the 

groundma. s i concerned i · the rock from Buffalo P eak, Park County, Colo., 

de cribed hy W hitma.n Cro. . li Thi.- rock j , o. 6 of tb a,bo,· -mcnti ned erie . 

It differ · on.·iderably from all th Crate r L ake ancl e. it , not only of this hut 

of other typ , in tb much gr ater abundn.ncc of th hy p l'.3thene and nug-ite 

ph nocry:ts. 

.HOLOCRY TALLI ' E TYPE OF A DF. ITE. 

The follo,ving ·pecimen · are placed under thi: type : No . 59, 60, 61, 62, 3, 

64, 65, 66 67, 6 , 69, 70, 71 72, 73 and 7-:1:. The: ar mos ly light-g-ray rock · 

with comparati vely roug-h fracture and with relatively incon picuous plagio la::>e 

phenocrystr. A few p cimen of darker color ar not thorough ly chara teri tic 

of the type. 

<•Bull. bidcm, p. 224. 
AN OR. 1TF. . . 

ndr r th mi c ro copr t hesr dcs tcs do not d iffe r y ry matcrirtll y in appear -

an c from th o:;r of th hy po ·rystallin r t.l' pc, wh en Yir wrd in whit!• lig ht, <' XL' p t 

tha t t hey a rc ntuch li o·h tc r in co lo r and :Lr entire ly f r .l' f rom g lobuliti · mattr r. 

B twren n o.· ·ed n ('O ~< , howc1·c r. the r i:; a twtrkr d d i If re nee h t wee n t hest' ;tndc-

·itc. and a ll the precedin g- type:::. ThiH cliif e rc nec is to be ~<e n i n t he gTo nnd ma:;,. 

The o lorl ,·s (·on,·ti t u ntH a.re of t wo el i. t inct ki nds. tir:< t. 1lagioelas la ths not 

mark d l,r diffe r en t f r om t b simi lftr la th,. in t b othe r a.nd sites· a nd , He o ncl . a so rt 

of r esidua l p rod uct of c r.vstalii zati o n ~cc urrin g in incguh1r. <LII otriomo rpbi c I atchrs 

that hrw c a poikili t i • a.1 peara.n c . owing to ·r oweled in cl usio n:,; of the otbcr g r ounclma.·.· irw r d ient.-; . The:< patch s 1·ar.r co nsid rahly in ·iz a nd in ('O nspi <' n cs~<, 

b ut in geneml are from 0.2 to 0.5 millimeter in d i:wwte r. Th y do not s how poly -

sy nthetic twinnirw . but Ycr.r oft n po ·sc.·s a ntorc o r lc>Js u nd ul ou · ex tin t io n. 

The) a r e q uite d i.· tinct f rom t b p lag·ioclns laths wh ich lie emh -dded in t hem tn d 

appear to plrty t he rol of a g las.o; ha:'ie. Tb in cl il'id ua l pat h s Hho w w;ually 

·imul ta n ous x tin ·tion.· a nd arc bounded only by mr t ing other simila r patch . .;. 

This a llotriomorphi c ma teri a l i.o; i n sonr c ease:; undou btedly q ua rtz : in t h r:< 

it i pro bably f !d.-pa r. It wa:,; p rov d to he q urtrtz in No ·. 63, 6(), 71. a nd 73 by 

it.-; slig htly hi o· h r r efraetiH' p ower a,.; compar ed with adjacent f ld,.;pa r <Wd hy its 

g iv ing a p ositive, nni<LXittl irnng in c rll'crg-ent pola ri~ d light. lt i:· co nHid r d 

to be so tim ~ f eldspa r f r t he f llowing rca. on;; : FirsL fail ur e to "how· uni ax ial 

imao·r,.; : s con I. o ·ca.-,io na l und nl u:; xti n ·tio n: t hird, .-om of t hr plao·iocla 

htths have rtll otri mo rp hi · xt nsio ns tha t rxting-ui:;h wi th the oute r p a r t of th e 

lath a nd r " IU h i tb >'<' pate hcs (G' . 1)-1:): fo urt h. in a f w of these tn dcs i tes 

he httb-' bap d phw io lase is n a rly mi,.;,.; ing so t hat t he ou ndnt :-; i:.; a lmo.-t 

ntircly compo d of t he ·e patch s, e xcep t for the inclosed a ug ite mi cr Jite,.; an d 

magn tit grain ·. If in lri ~; Ia ·t <'<VC a ll t hi:'i mrttc rial we t· y ua rtz . it would g i e fL 

r o k far t a id ic in compo:-; iti n to he clas:; d a:; rtn nnclc:<itc. IYh c rea ' th o~; 

a . . ·o ia ti o n a nd rcsemh b111 c h e tw n all of t hese roc ks ntn k it impo ·ibl c to 

·cp:tmt ftny o n f them fr om t bi · family. 

Th m or e cham ·tcristi c of th c 'C holoc rystallin r ftnclc;.; itcs ha 1· a g r eat nh un -

dttn ·c of w H-d rtin ed pl aO'iOC' lasc lath,; wi t h flui dal anang- nt cnt. a · w >U a::; innume rabl e rtu ito mi cr olite ' itnd o tah rd ral l'l'.l',.;ta l::; a nd g rains of magn titc embedded in 

n hasc of th e all tri omorphi p ntclw.- of fc ld:-;par a nd of q ua rtz (60, 61. 6(), 71. 

74). The rtug ite mi cr o lite · arc, 1V a rul e. somc lrhat. lnrg•r and n q uit so ::;h1trply 

d v lop d a is the ea · in th oth e r rtn lrsitc.. Th ph oc y~< ,.; f plag iocla::;e. 

h y p er the ne and n.ug it cl iff r in no t ·sr ntial r •sp 'ct front the cl ·c ript i ns g i1r n 

for a ll t he rat r Lak 1tndc ·itcs. F ig . ('of P l. XVI (p. 98) g ive:-> a fa ir i lr a of thr 

allotriomorphi · pat h e. t ha t eh1tnH:tr ri zc these ho loe rystallin c a nd ·ites. 

The pre ·e nec of quartz in t b g ro und mn:;s of the · r ock s .- uggcst.-.; a mu('h nlOl'<' 
90 PETROGRAPHY OB' ORATRR LAKR A~l'T. ONAL l'ARK. 

acid ro k than the chemical analy c of rater Lak and ito · g iv n rl rwhere in 

the ·e page:· ~t ll ow. · the on ly analy i made ~f thi h l r '· tall in ' type i of o. 

6 , whlch is not thoroughly r pre · ntntive_, inn mu h ~ th a,llotriornoq hie patch l:l 

arc not v ry w ll developed it will b of inter ·t to com par' the ·r rocks with ~t 

. imilar rock oil ct d b )lr. Dill r n.n l ~tllu led to 1 y Mr. H. \"\ . Turn r in hia,rticle on the Ao· and uc s. ion f the Ign ou ~ Hock" of be i lTH. Nevftda. " Th 

ro k in que,,tion wa taken from Crat r P eak, Cftl ifornia La,.; ~:Jr n P ak qu adrangle) 

an l i:; o. 1 29 of tb Cascad Ha.1w collection. Mr. Tnrn r doe.· not d cri b the 

rock, but be refer.' tojt a a pyrox ne-and ite and give · the chemical analy i mad 

hy W. F. Hillebrand. b Thi. analy. i will be foun l l'CI ated on pR.ge 94 of thi::: 

paper. Through th e kindn · of J\lr. Diller the writer wal:l nab! d to -tudy a 

thin section of thi. Crater Peak and site and to omparc it with th thi n . e~ti n 

of the r ck .h re under eli. C!L'; ion. \i\ ithout any noticeabl differrn c it appear. to 

b identieal with th Cra.tcr Lake holo ry k'LWn typ of and . it . Thi. · i · tru not 

only of th e groundmas , with i · allotriomorphic patcbc. inclo. ing· plagioela e lath · 

and augite microlite etc. , hut al · of th ph no ry t. . It will b .· n, in comparing the analy. i ·with tb anal~· e ' of otb r ande itc · from rat r Lake, that thi 

· ntain. b twe n Hand 10 per cnt mor ilica. It i ·, in fa ct. l · l y ana logou,.; to 

the dn.cite ', su h as, foT in tan e, those from La n Peak a nalyz d by T. M. 

Chatard and Vv. F. Hillebrand. c It i highly probable, th r efor , that th e and e-

. ito · are, in part at lea -t, dacite::;, althouo·b no w 11 -dcfi n d qmutz i · to be en in 

them. 

r o. 19 probably belong with tb holoery tallin and ·ite , but owing to 

cxtcrv iv altNation i !:l characteri. tics are not r adily made out. Th groundma. · 

con ists of much homoo-eneou -lool ing chloriti c matter, with rather faint lath- hap d 

plag io ·In and not a little allotriomorphic, colorle. :- material that i. probabl 

feld par. The magnetite ha · been alter d to leu ox n and th pyroxene of both 

th e ph nocr.v t' and of the groundma · · to chlorit . Th pben ·ry tic plagio lru ·e · 

ar partially a lt red to carbonates Lod prohably to kaolin . A (J' od deal of quartz 

:is to be een in di tinct grain , two or three of whi ch ar quite larg-e, while tb 

re -t oc ur in bun hes of al lotriomorph ic grain . A,.; thi i · th e on ly a,nd it 

from Crater Lake that ·how. w 11-d fin d quartz, thi. mineral i in thi c-a.·e 

probably econdary in origin. 

These holocrystalline aude. ite , a i · the case with th other types, ar w·idely 

di tribut d over th e Crater Lake area. Ther may he ·orne .·ignificance in th fact 

that . ix out of a total of fifte n ar situated at th water edge; that i , a large 

proportion of them belong to the olde t lava fiow.· expo. ed. o. 63, which come. 

from the ba alti · ·one ralled Crater Peak, south of the lake, i · taken from an 

t' j ted fragment, an l wa doubtles~ tom loo!:le from a deep-lying rock be low. 

«J our. Oeol., Vol. HI, 1 95, p. 410. b!rl m, p. 407. ,. Bn ll . . . Geol. Survey No. 150, l 9 , p. 218. 
A DE !T E . 91 

DA ITIC TYPE Ol!' ANDE. ITE. 

This fourth type of ande:;it i.· int rm diat h WC'en the and . ite · and lnt it<'s. 

but seem: to pos::;e -.. chara t ri. tic' that ally the rocks her in lud d mor ·lo ·ely 

with the ande, ite:; than with tb dacit . It i · 1 os ibl that a chemi cal a nah· i · 

would pla e on or two of tb m in the li. t of da ite . 

Of th . ix sp ·imen.· placrd in thi g roup, thr ee (75, 76, 77) hav th da itie 

feat ~< particularly prominent. The g roundma ·s in th s thr C' ·on: ists \'Cry large ly 

of :l nearly eoloriC'ss g lass in which li e my ri ads of the r xtrcru ely minute r d-lik e 

augite mi r olite · chara teri tic of tb g la' ·y dacites (77). ln two (75 76) thC' 

groundmasf'l to nsists of :omewhat larger 1i1i ·roli tc of th same mi neral inclo;:;ing 

minnt black spe ·k:; of mag·netite or 1 o sibly of o·lobulites, SHO'O'f', tive rather of th 

andesite . In add ition to the e augite' mi ·rolitc·· ,. ry ·1< nd r frld p<H' microlite · a:; 

wel l a · a f ew oth er lnrger and broader plag io la cry tal ·. ar .'pa,ringly devC' lopf'd . 

The gln.·s l a.'E' is r nd r ed dnrk looking, c ·pecially in No. 76. by globuJiti · inclu ·ions 

and hy th presen e of a very little mao·n titc. In No. . 76 a nd 77 o •cu t' deep 

ru. ty-hrown and ·omewhat granulat-d spo s thn.t tend to fo rm around the po r<' ' 

a,nd al. o to ·ome extent around the p lag ioda:; phenocry ts. Th pore · nr :lpt 

to ontai n a li ttl tri dymit , pat'tially o r entir ly fi llin o- them. Th se darker. ironrn ~<tf'd spot:; hear a ·li o·bt r e:emhlancr to the ·pheruliti e g r wth.- in th dft ites, 

hut lo not app<'a r to pos:es: radiated :;trnetur . 

Tlw thr c oth r ·p cimen (T 7\:1, 0) ar ·imilar . . o far a the augite 

microli t .· ar e o ne rned; hut th y co nl:.'tin ]itt_] o r no glas. ba ·e, in. tr ad of which 

th n' is to b ·een mu ·h more abunda.nt plag.io ht' lath;;;. as well a:; ~<qmtr h or 

sho rt r ci:.'l ng·ular fcld. par" with undnlou ;;; xtinction or rath r. wi t h ;, nal strnctur<' but n twin o i ng ; J ikewi ' e rna 11 i rreuular or itllotriomor phi olorle:. shr d · of 

fold ·par or, p ·dmp. , of q ua.rtz. 

Th ph no ·ry;-ts in th s ·ix r ek a r not . ntially differ n t from those in 

other a nde it s (brown ula,-;s in I : ur :;. abundan in 1 lao·io Ia e of 75). Hyp r-

;;thon<' in two o· -neration,.:;- tb older in : hort stout, and r latively hlro·e cr y i:.'ll:, 

th yonnger in . m, ll long. a nd lcndcr pri:;ms- i;; clear]:· d ,. lopC'd in No. 7 . 

The last thr r r ock:-; . withont per ceptihk gla::::;; . a rP Ye ry li o·ht ·olored in th 

hand 'I ccim n:; whil e th e g la .Y ya,ri tie · a.re much dark r. 

ERTAIN T PE . 

With th f'xception of tho r f " i;,ard I land th a nde it lava of Crnter 

Lak do not appear to be di. tribntcd in a.ecordance with the typo · her ein described , 

but the variou typ occur over all the ar ea, ~tmo g both th old r a nd the 

younger a nde ite flows. In the ca · of Wizard I land ft p::trtia l cxc ption 111 ay be 

notP.cl i n that the mor tho roug-hly l'l'~' talline t) pe · ar e almo: t wanting. The 
PETROGRAPHY OF CRATER LAKF. ATTONAL 1> RK. 

and itc: of \Vi11ard [.land nrc unu m1lly black <lnd ha:;a.lti -looking, a nd ontain 

much brown O" la.·,;. Otwa,.ionally they arc ~(}l in d <t clrrp brownish red by iron 

oxid ( 7 !J). 'onw of h more o·la;;sy hhtck portion~ s em to ba Vl' ern eked i u 

the 1ro ·c ·,; of uoolirw . the nack cl .-;urfnn ·; being left with a, cl cid d g loss. Tbi 

was parti ularl.v noted n a specimen collected by the writ r from a lnrg·e block 

in the ·rat r on th summit f the i, land. 

Of th , thirte n rocks from \\ i11ard I.- land ~tudi d in thin i'le t ion, fi,, M of 

the hynlopilitic typ : six of the bypoerystallin typ . suhtyp Ai two of tb same 

type :ubt,,·pc w while on ly one, and tbi: a somewhat doubtful on . is of th 

bolocr . tx'tlli ne t)·p . 

mong· tb <tnde. it s co li cted I y Mr. ,1. . Di ll r on \\ izfLl'd J. ·land ar t n, 

No. . 1 to 90 intlusi,-e, tb · exact lo ·ation of which is no gi ,·cn. Of tb sc .r o. ': 

bas no co rrespon ling thin s tion. The oth rs do not vary C>T atly from th oth r 

:pecimen. f rom this iJa,nd cnum rated abo ,· . Nos. 2, c6, nnd ar plac d in 

tb hypoer. ·. tx'tllin t,q.J , suhtypc ; o r po::ibl.'' :2 might cq nall)· w II b put in 

the hya,lopilitic typ . ~o. "-1: i . .,; a, hyalopiliti · ande. ·it . i\o,;. H , ' H, and 90 arc :o 

strongly imvregnated with r d hetnf tite powde r a. not to b a ily clas ·iii d. They 

ar probably of the h,,·po ry. tallin typ , :ubtype A. ?\o. ry. tallin 

ande ·ite with basaltic appearance. It contnin· sma,ll augite pri ' tns too la,ro·e to be 

called mi crolites, and also con ·idcrablc ,tll otriomoq hi fe ld. par in th groundmas:. 

hut no poikilitic pa,tcbc.· su h as <· ·ur in lliOst of th holoery ·tallin andesit ·. 

At th bectd of ' tee! Bay, just to the cast f Llao Ro k occurs an ande ·itic ro k 

lo. to th dik fr Ill whiuh :Ko. 96 (page 93) was collected. Thi · andc. ite i · r pr -

. nted h,r o. !H . ft nd i,· a nearly hc,lo ·rystallin · t'O k with very abundant ph nocry. t · 

and with a. g roundma ·: that r~ miles that of ~o e of th ba. a lts, notnhly No·. 176 

and 177 of the porphyriti · inter.· titial basalts. The main feature: that di tin ui h thi · 

rock frolll th e ba aJt.- ar the ab:;enc of oli,·in and th Ycry marked porphyritic 

clc,·elopm nt. Thi · a.nde it do » n t clo:ely r esemble any tber ande ite f rom 

Crater Lak , at 1 a t not lo · nough to ju tify pu ting it in any of the abov -

d : Tibed types. lt more clo ly resembl · th ba:alt: than any th r rock oil ct d 

on or within tb crater rim. 

ANDESITE DIKES. 

With the exc pion of two dike. under Llao Rock all thr dikes that cut the 

walls surroundirw th la k belong, al':! far as may h judged fronr th : pecimens 

oll ected, to tb andc ·ite . . 

Two : p ci111cn. we re ·oll ected from the rather large dike that run diagonally 

down from The \.Y atchma,n to near the lake lcYel. Tbe e two ·pec imen. (92 and 

93) may be lets ·ed with the hypocrystall ine a.ndc itc..;, : uhtype B. The ph no-

('J'y st: do nut prc:cnt any spcc i:tlly di~tinctivr fcaturrs, hut the gTound nJaSs of th 
A DEHlTJ<:S. 93 

two ·pecime n::; show · two extr mes. ~o. !l:2 i,.; rchLti1·e ly con,r:-;e gmi n<'d and pre nb 

a tra.n ·iti on to the ho loc ry. -tall i ne type, in which how v r, the a llotri morpb ic pat he,.; 

ar .- uppr :;::;ed. It ~-; furt:.h r chn,mete rized h.r the pre en 'C of unu,;ually abundant 

plagiocla e lath;· of a ve ry uniform and fairly ln,rge .' izc. , o. H3, on the oth r hand, 

m~L.Y b con ·id r d as trau.-itiomd t subtyp A in h~Lt the pla.g ioc la.-c lath:; .- ink to 

minut siz . But thi · g r oundmass :d ·o ·onta in · a gTl'>rt man~r ·qua rish or short 

rectarw ular fe ld::;par · that ·ug,. st lln n,ffi ni t.1· wit h ·tb dac ites. 

Fr?m t:.bc upper p a rt of. tb d ike !:.bat. lie bctw en lat' ier P a k a nd The \Vat ·h -

man o. 9± wa · ·ollectcd. In th hand specimen thi" pre.- nt.- a strikingly uniform 

appearance. It has a mtb r ligh -gray ·o!or is ,. r.r p rous, an I at a ca;;ual o·la nec 

app a r · to b f r e from ph noC'r.v · ·. On the contrar.1·, ph nony:-:. s ar ,. r y abun -

dan t., as in t hin ·ect:.ion t hey appe:< r to f rm rLbout on -half of. the e nt:.ir nHt.-;;. Thi.· 

i · in fa. 't, a t horoughly ·haracteri ·tic a ndc,.;ite and i.· ,. ry .·trongly p rphyrit:.i ·,wit h 

great. ·ontra:;t bctw en be ph no 'l'_l'::;t:; and the groundrna:· ., P lagiocla,.: , hyp rthene, a nd augit are a ll ab un da nt. Th pyroxcn occur both in .-harp c ry tal.- and 

in ne.-t,.; of granula r incli,·icltmls. The feldspar e ·u r.- in two distinc-t ty r c· ; in t he 

larg r ma ny-fac d fo rm · ha1·ing th euHtorna r y g la ·:; inclu.-io ns. and in tb e :;mall er 

r e ·tangu lar fo rm . From the cbara. t r of the g rou ndnHl.' ' th i · rrt ay he 'On ·idcr d 

a typical illu -tration of tb bypony.'tn lline t:.ype, ubtypc A, chara teri z d by th 

abundan e of minute plagiocla · mi crolite·· . 

The a na ly ·is of this ro k i · u·i 1·co on pag 9-l:. It i ndicatc · that t:.hi ' i.-

thoroughly r pr ' Cntati1·c f th 'rate r L ak and sit s. 

ndcr h nort:.h nd of Llao R ·k cu r" a <li ke of which Ko. !)~ i.-a .-rt.m[l e. 

It ve ry clo:-;c ly r mbl s th rock just d sc r ibed. nd cr t:.he rni ro:;eopc it npp ar:'l 

thn,t t h pheno ry ts ar not quit ·o alun lant a nd not :;o unifo rm in siz . Th e 

gr undma.· · co ntain · cons)dernbie a llotriont rphic feldspa r. " ·hi ch to a ce rta in 

ext nt hide the rni ·roliti c plagi cia · .-. lt l c long · with tb abo ,·e-de.-eri becl rock, 

to ·ubtype A of th hypo 'l')'otallin , andc ·it ·. 

At the h ad of 't c l Bay, a littl to th ca t of Llao Rock, o ur.· ~· d ike 

from whi ch }lo. ()() wa,.. co li ct d, whi ch Hhows under th ntino,..cop a. ,. r y pr tty 

lc1· lopmr nt of t he byaloprlitie structur . r~· abundan t p hc n nysts of the 

cu,.;t rnn.ry ·harn.ct r:; It embedded in :L g roundllta:;,.; co .- ting of tl d p -brown 

gla:;s tbftt app ars to irnprevnatc a I o,.;ely f It d aggr gat of sl ndcr ftttgite a.nd 

1lag i cla c mi ·rolit . The g· la.-:; ba ·c '"' f r , o r nearly h e', frorn g lo bulitic 

ma tter, but co nta,rrl ·. in addition to th abo1·e-mc ntion I m1 crolit ·, octahed ral 

·ry.-ta l · a nd g ntin,· of mao· n tit . 

On the a:;t sid of the Ia ke ar to h0 seen two dikes ncar 

o f t h<'.-c (33) oc ·t~r s exaetly b lo w :::; ntincl Rock n.nd th e otlr 

e ntin l Rock. One 

r (21) about a thircl 

of a rni l ' to th(' no rthca,.;t. Bot h o f th<'HC ro ·ks ha1·c air ady b en rde rrcd to 

in conn ·tio n wi ·h th d ·crit tio n of the antic ·it ·. No. 33 b longs to t he subtyp A 
04 P E'l'ROGR A:PHY 0.1<' RA'J'J<:l~ LA KE ' A1'I ONA L PARK. 

of the hypo ry:ta.lline andesites fLnd I o. 21 to tho hyalopilit ic ty po. \ ' the c 

ty pos hav been fu lly de.' cribed abov , a repetition he re is lm rd lj n ·e ~a l'y . 

1n co ncluding the de ·cription f tho ando ·ito in dike form, we lllfL.I' not • that 

many of the Vfl.l'iou · type found in the ande ite fiow::; are ropefLted in tu o d ik :, while 

110 umrkedly differ nt ty pes have been wet with in t he dike aude ·ites. 

CH E MICAL ANALYSES O F AND E SITE S . 

The amtly.o;cs o·iven in the followi ng tabl a r a,ll of Crat r Lake ro ·k ', wi t h th e 

exception of the la ·t, which i · from Crat r Peak , Ca,lifor nia,, and j s ·iven fol' colnpa l'ison. The ann.lyEe · were made by the ch mi ·t:; of the United tatt'. G olog-ica l 

Survey. Tho munbers at the head.· of th column · arc tho -pecimeo number' . 

Anaty.~ of Crater Lake andesiteJ. 

(Analyses by H. N. 'tok •, except of I 29.] 

'iO, . . ...... . ... . ......... .. .... . 

Al,03 • •••••••• • • . • • • • •. ••• • .••• •• 

Fe20 3 • •• • •• ••• . • • •••• •• ••• • •••••• 

.FeO .. . . . . . . . . . ..... . ........... . 

:'IIgO . . .. . . ..... . .. ... . .......... . 

'aO ... ........... . ........ . .... . 

Na., 

K,O . . .... . ... . . . . .. .... . ....... . 

H, - .... .. ........... . .... . ... . 

Jl,O+ ...... .. .. .. ..... . ....... .. 

TiO, ... . .. . . .. ........... . ..... . · 

Zr :! _ •••• ·- • •••• • •••• • __ _ • • •• _ •• _ 

0, ............ ... . .... .. ....... . 

P,05 .••••• • • •• • •• •• •••• . • •.. • ••• • 

• Os-· ·· . .. . ..... .. . . . ... . ... . ... . 

'l · ·· ·· ·· ··· ·· ····· · ·········· ·· · 

F .. ........... . .. ...... ...... ... . 

I · · ·· ···•··· ·••·••• • ···· · · · ·· · •·• 

'r,03 • • • ••••• ••• ••• • •••• • • • • ••••• 

KiO . . ........ . .... . . . . .. ..... . . . 

MnO . ... . .. . . . .......... . ....... . 

13a0 ... ... . .............. . ... .. . . 

Li,O ... . ... . . . .. . .... ......... . . . 

T tal .......... . .... . . .. .. . 

25. 

ii9.39 

1 .r 

1. 79 

3.90 

3. 13 

6. 29 

-1.29 

1. 29 

0 10 

.-!2 

. .JL · 

~on . 

'one. 

.22 

."\on . 

Trace. 

Undet. 

X one. 

'one. 

X one. 

Tra e. 

.05 

0 0-! 

Trace. 

26. :~ 1. 

5 

17.85 

2. 67 

3. 2!) 

3.61 

. -!5 

.71 

X one. ' on 

N ll Jon 

017 .2-1 

X one. None. 

Trace. 'fra e. 

ndet. Undet. 

~on 'one. 

Kone. None. 

N ne. Jon e. 

Trace. Trace. 

.06 0 05 

0 05 . 05 

one. Faint tr. 

99.71 99.87 

I 

6R. \l.J. J, 2!l. 

1-

62.09 I lill. O~l (j 012 

17. 03 ().2~ 

2.3 1. 2(i 

2.0 

I. :;.-

!). 6!5 H. 0 

.J . 10 3 . !) 

1. 67 2.5-l 

. O.J 0] 2 . 40 

0 13 0 2(i ---------- 0 6~ ·' !54 0 2ii 

X one. Kon ·····-- ---

None. ~o . I 1' . 19 0 23 

Kone. Kone. 

Tra ·e. Trac 1---- -- ---- U ndet. nd t. -- ----···· 

X on 'X nne. --- -- ---- · 

'on ne. i\one 

None. 0 05 ------ --- Trace. Trace. 0 J(J 

0 07 0 0-5 . 09 

0 07 . o- .02 

Kon e. Faint tr. , ___ Trace. 

99. 4 100. 2R 99. n I 

-2------~------~----~-------------- NOTE.-0= I. 
ANDE. I'IE . \1 5 

No. 25. Jl ype r,;thene-andesite, ypoe r~ ·stallin typ , ~ubt pc A. west, ctg' f Wizanl lsland. 

, e page 6. 

No. 26. Hypersthene-ande·ite, h,vpoC'ryRta lline type, ubtyp " • rim jut Routh nf Th E' 1\'a tehtnan. ee page 6. 

o. 31. l.lyper th en andesite, hypoer.vsta llin t~ pe, Qubtyp .\, a.t. the lake Jon:l undor Lla" 

I{ ck. • ee page 6. 

N . 68. H_vpersth n -andesite, holocry tall ine type, Palisades, 1111\l r Round Top Oil L110 Horthea:-t po rtion of th e rim. 'ee page 

~o . 94. Hy pe r thene-and ite, hyp y~ta ll ine tn e, .·nbtype .\ 1 from a larg dik entir ly tmn;;-

cting th e rim betw en Glacier Peak and Llao Hock. • ee page 6. 

~o . 1 29. Of t he Cascade I anae oil -lion, a r ck called by :.\Ir. Turner a pyroxene-an l >'ite, 

holocry talline typ . From rater Peak, ali[ornia. Analy i by I V. F. Hil lebrand, taken from 

Bull. . . 'eol. urvey Xo. 60, p. 157, No. 19. ee page 90. 

It i a little urpri. iog and al. o unfortunate that out of five. p ·irncn - of n.nde ·it 

eel ctecl by Mr. DiUer for chemica~ analysi.· fo ur should turn out to b loner to on 

type, and thi not the mot common one. It i.· urpri ing, b cau:;c the. c ·1 ecim ' rL' 

were . ·elect d with a view to repr . ·enting typical o ·currence. . \ the -ele ti on wH. 

mad b fore an opportunity wa · g·iven for micro;;copie tudy, it wa · impo::; ·ible to 

distiugui h the different type · from th hand ·pecim n alone. 

SECRETIONS IN ANDESITES. 

In a number of the and ite rock. at differ nt localitie. ar found inel . urc or 

nouul :; that a)Jp 'ar to be ecretion of the IDOl' ba:i minerHl' . 'om time: t.bc ·c 

i ncloi:iure ha\· mor or l · · rou ndi h form and ur ,-idently inclos d in the en::; 

tha t tb y a rc not; literally form d io pine'. Thi i · particularly viti nt in a p cint n ( -) ollcct d in 1 '3 from tb south rn rim of th rater. Th ro ·k i ·elf, of 

which no thin · ction ba::; be n made, ha a nearly 1 lack groundma: '-whi ·h i::; 

probn.bly h_ alopil itic- inclo· ing numerou' and very con ·pi uou pbgiocla c phenocry t:s. Emb dd d in thi ~ ro k i.-a roundi'11 ma · 2 or 3 in h in diameter from 

which th ande ite app ar- to hav hrunk away in coolino· as though fronr £L 

f reio·n inclo. ur . Th in lo ·ure i blacki' h g-ray, compn. t, with9ut; phcno ry t::;, 

a.nd li o- ht;ly porou ·. It ba ' a v ry ba ·altic look. 

In thin ction t hi pe im n i · fairly chara ·teri 'ti of mo ·t of the inclo:- ure . 

H con. i ts of a deep clear-b rown gla:. in whi ch lie in loose! · f lted armngem nt 

·lende r and very hrtrply d tin ed lath. of plag io •Ia .-c and equally >: lend er but not 

alway.- :;o harply cut pri m · of hyp r then and augit · al ·o a little mao·nctite in the 

<·u ·toma ry octah dral form. Hyper, th nc i. more abu ndant than aucrite, but both 

ar e much mor abundant than i · u ·ual in th a.ndc-it s. The two pyrox ne 

appear to form about a large a, per nta ·e of th e rock a doc the plagiocla. e. 

Pamll lism of g rowth b tw n t'IJ c augitr a,nd hyper;:;tb n i common. The lerlO'th 

of the:c pyroxene- is often t;en tiru . · as nwch a · the width. Th 1 hwioc]n. c is 
l'ETlWGHAl'HY OJ!' l~ATEH LAKE NATlO AL l'Al'tK. 

ntth r simply t\\'inncd with b ut two or thr ee b::tnds::tn l show.· large ex tin ·tion ftn g le ·. 

They ha ,· ·qmtr cro · .· ·tion with dino·onn.l extinction. Pb ' nocry ·t. · ar entire ly 

wanting. 

F ig . l of Pl. XVl prc.·cnt: a photograph o f thi: thin · ction in polarized lig ht 

a nd Fig: }) of II. X I l1 photog-raph o1' thin :; tion of No. \)i n white lig ht, : h wing 

both th ecr tion and tb in losi rw hya lopili ti ·and itc. 

Analogou.· to the abo,·c arc . 9. f rom th pH,th thHt leads J'rolll the Hlllp 

gronnd do11·n to th ,·vater·:; dgc; 1\o. 16, from K en ::\otch. a t t ht' bead o1' 'and 

Cr eek ; a.nd No. 75 from ncar t he road on Anml Cr k. The:c thr :;p e ime n · con-

·i: t of ·mal l inc lnsions in mther g lassy a.nd :; ite ·, th e f"ir:;t t\\'O of t he hy;dopiliti 

and the last of th dacitic type. The incl usions form only a small part of the thin 

ection in acb <:a ' e. 'fb _\· do not, hO\\'ever. ap{ ea r to 1 e fo r ign to t h rock. 

On th e contrary, t he junction of th :ecr tion \\'i tb the :;urToundi rw and ·it i. ·n 'h 

<L: apparently to preclude the icl a of a n entirely · pnratc orig in. The ·l ear g lass of 

the ecr eti n is exactly of t he :;am olor as that of th main r ck a nd th j un t i n i · 

not :·harp, but th ing redi nt.s se m to htw c oTown fr m the :ccr tion out into th 

surrounding rock rna. . The tir -t two contain phenocr yst: of pl< o·iocla:s , and to a 

le ·· extent of hyp r th ne similar to th e · LT ·ponding phe no rysts in th in losing 

an ]e ite. ln son1 e ca e · one of th plagi c- Ia ·c ph enocryst app at·: to h lorw 

about equally to th seer tion and to the mn.in mas·. 

res mbl s an enla rged ar a lik tho.·c on f r· quently meet · with in t h m r g la · y 

a nde ·ite·· of Crater Lake, \rber e a de p a nd cl ar br own g la s, fr e f rom the cu -tomfll')' mi rolit s occur ·. tiJlirw th e ·'I ac betw en two or thr e adja · nt ph no ·ry:ts. 

No. 9 ' i. one of th e ·e inclu ion · f rom a lar ge bowlder b -t ween S ttn r e k and 

and 'r k. 'Ih rock in whi eh tbi i in lo · d (76) belongs to the dae iti c type of 

ande:" itc, rtnd has a.lrea ly b e n d ·crib d. ThL in lusion contain: large, cham teri. ti · plag:io ·Ia · pb no ·ry t · that a r cr owd d 1ritb the usual in clu ion. , a nd that 

pr s nt d ar margins; it co ntains aL o phenocrys · of hyp rHth ne. The g las i · 

·tain ed a ,·cry d p r ed \ ith f rritic matter. 

o '. 99 and 100 a r s erctions in the abo ve-de:cri b d hypocrr talline a.ndc:ite (40) 

found a t th ·pring- near t he camp gro und. They both r esembl e N . 97 in b ing 

nt ir ly without phE' no 'l')' ·ts and in ha ,·ing th :am f lted : tru ·tur a nd the Hame 

compo.-ition as that r ock but they d iffer materially in that Cl'}' tallization appea rs to 

bn ve p roCJTe:. ed un til bu t li ttl g la ·· r emain:, and thi li ttle i: n arly ·o lorless and 

not readily d isc rnihl . In fact the:e two inclusion: w r c at tint taken for basalt 

in lo:ed in tb 

the e and th 

[tndc ·ite. a nd wer e it not for numerou · int rmediatc tage u etween 

mo re eYidcnt :ecretion s t he d te rrnina.tion as basalt mig ht hold . 

Othe r ca: : of s c retions rcs<'rttbling lms:tl ts arc mentioned in ·onnection with the 

desc1·iption of th e dacite · o f Crater ~Lkc . 
PLATE XVI 

• 

9255- No. 3-02-7 · 97 
PLATE XVI. 

TTTI~ E 1'10 . O F AC\DE ITI,; . 

F 1c: . / I.- crel ion in and .. ite f1 ·om t he , outhern rim ol th o <·rate r. :IJ>wnifi •d . d iameters. 

F;pecimen No. 97. .\ photomicrograph in 1 olarized light with ro~sed nicol.. The ct on •·un-

~i -ts of a de p-brown la~;; in which lie well-defi ned htths of pifwiocla.·e and equally nd r pril"m 

of hypersth np arul augit ; al~o a little ma netite. The pyrox ne. ca n not w II b• di tinguished 

from t h plagiocla,·e in the photomicrograph. Se pao-e 9 >. 

FrG. B.-Anrlesite of th hypocry tallin type, from Ca.th edt·a l Ro k. ;\fagnili d 20 dian11't ''"'· 

Bpecimen o. -!5. A p hotomicrograph in whi te li«ht. The ragg d black -r~ tlll is a brown hornblend almost romp! tely altered t hrough r. oq lion to a hla<·k aggrega.t of magn lito and Hn).!itr>. 

Th F ction al,;o sho11·:; two gene rationH of plagior.la ·c. Th large phenoc ry. ton th right n·pre nt l; 

the oldest 1-(enc ration wi th •lass in lw ~. Fo r dc~c ipti n Sl' 1 ag , 3. 

F1 :. .-.\ ncl site frum the wat 'J · edge at the I wad of • 'nn C'r ek. :\[agnilled -! d iamut' ''"· 

.·p cimcn No. 73. A ph microgr~ph in polariz d licrht wi th n :sed nic l~ . lllul"tra tes the third or 

hnlocrystalline type of andcsit and i~ characterize<! hy t he present of allotri omorph ic patch'" of 

fc ld. pnr, which appear RS light sp If' in th e photomierograph. · e page 9. 

F11:. /J.-AndeFitc from th e pat h I a di n' from I he camp ground to t h water at Eagle O\'C. 

"'lagnifi 'd ~ d iameters. Specimen Ko. 9. , holl' t h junction between a hyalopilitk aude it ou the 

right and a~ l·retion in the ~a me (Ill the le ft. Th ~ <·rl't ion co iFt.,.. of a decp-bro\\·n g-laf';; und ·lender 

lath · of plagiocla .• and pri ~ <) f hype1 ·th ue <U td augi w ; ~o a liltle Ulagnetite. e page 96. 

9 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 3 PL. XVI 

(D) 

THf 1.1 (11100< 0114'11,.'!1( CO. 

DA l'L'E . . 

Tn - . ~, ft hypoe rystalline amlesite from '' izar<l Tsland, is to lJ s e n Hll 

in<:l o.-ure that may wi th lll ore probrtbi li ty In• take n for husalt. Thi;; co nsists of slllall. 

irreg·_ular, a nd :Lpparent l.v iso lated gra ins of augit , or pos ·iblY of hypersthenr - th ' 

di.-ti nd ion is not terta in in this uvr- that oxti n<,·u ish simu lta.neousl_,. on•r ·onsitkrablr arr as. Th ' space.- uetween thc:;e gra in :-; :li'P fill c1 with ·hort and not \'C'l',\'Hh:t.rp 

plng ioda,;<' lrtths . 

. \rock coll cdl'd b_,- th writ r f rom th e bottom of th ' ·mte r o n Wi;mnl Island 

(:WL7, +of t he print.t ' coll e ·tion of th ' writer);; 'IllS to lhrow HO iliC ]io·ht on thcs' 

see r tion.-. In the hand sp ee i111 en it ·onsist.- of a rath r conqxtd and no nporo u:-: g- ray 

and •site, with it-r 'gular. li o·hte r g m,,- patc· h .- se :~tt cd promi.-cuously throuo·h it. Tn 

thin · <:tion th e.· li o·htor patch s are .-c n to b • holocrysbdlin , with'" g rou ndmas,; 

co1n p .'eel f plag io<'lase, augite, and Jnag nt'titP. Th e plagioda.-c i: htro· ly in th r 

form of . bort lath ·. but betwren these laths th e saul mine rnl appNm-; in allot.·ioulorphi e fo rm. but not in p oikiliti patehe::;. Th <• darke r portion:; of th ro k do not 

appear to diff r from thr li o·hteqntrt, CXtt'p t that th all otrion10rphi · feld.- p:-tthi · 1 art 

of the g ro undula ... is I' ria ·cd h_,. a drop ·lea r-b rown g la::>s. That ·e ,- nd i'Ut'h altt' l'-

nation,..; in the g rounclma · · nifty occur within th a rea of a thin ·tion mak .- it more 

likely hat t h appar nt i nclosure,.;, in whi ch brown g ift.' ' i.- ·o very ·onspi ·uo us ar' 

o nly loc-rd cl if:l' •r c ntiations in a com n1on nuwma. 

1I Y PB 1-t::n• U KN }!;-DAC.LTJ< ~. 

In ;til the cl :-: ·riptio ns of tlw r oc ks of rater L ftk h retofor I uhli ·bed tb' roek 

which arc h ' I' ' d .siu·mtted as dacite.- hfw b '•n callecl rhyolit Thi.- i · not to he 

wo nd r cl1tt rr.- th e:;e ro k · prese nt all t h outward ebaract ri -tie · of rbyolit · and 

\'(' n a mi cr .- OJ ie examinrttion doc,; not at fir::;t g i ,. str o nu· o-round for the r hanu· 

of nam<'. Pre ,·i uH de::;cription~< ha,- hrcn ba.-ed larg ly upon fi ld obs rntt,io ns. 

But, in H[ it of the fa tba,t coni1 a rison Jll:l,'" fr '<] U ntly h nmd and i · made in thi.-

1 a per h •twren t])(•>:c dacite · an d rhy oli te. of w ll-known oecurr n . 1t arcful r:; tud_r 

of th ' min ralog in d ha,ra etl'ristic ·,; . .- upportcd 1,_,. th h mica] nnaly ·p,..; h1tH led tb 

' rit r to th con viction tha · the <' h~Ln g of nanH' i.- ju ' tifiPd . \:;.; will appe11- r lat r, 

the de tr rlllinatio n o f' t h(•,.:(' I' ·kH fll'i da ·itt's j,; f urth e r str e ngthened by re ·cmhlan ec 

tooth r claeit r:; in tb ' adja ·c nt n 'g ions of no rtht' rn (} tlifo rni fL. 

\ :; wil l he .-ecn to l~t• til(' ca..;<' with thl' haHalts, the dacite · of 'mkr Lake arc 

so1newhat lo ·al in Lh •ir distribution. /1.. · th '.\' ar ' chi ' fly ·o nfi1Jl'd to di.-tincti,- lam 

f'low tbnt, with o ne rxecption, r cpr · nt t he Ja,t .-t rupti n · to I> -e n o n th 

rim , ;tncl wh ose ontline · v:tn he ddinit; ly tnwed. it is po iblc nne! desirablr to trcaJ 

l' :l h o f tlw cla c itt' flow" S l paratl'ly. B o·innino· with the most conspi 'llOus flow, that 

f Llao Ho('k. :tnd pa, .- inu· :tround th' htl e toward the a. t, the dac it t-l o w · will l c 
100 P Kl'JWGRA I:'HY 0~' RATE!{ KI ~ AT W A IJ PAHK. 

described u nder the followirw head : Ll ao Hock G rouse Hi 11. 'lcctwood 'o, , 

\i\ ineglass, loud Cap, un r k. Ou t ·id' of the: . ix a r eaR fts ' II as within the 

t>a m , th r o ·c ur~ abundltn t clac i ic mn,tcria l, in the fo rm of bomht> <Ut<.l tufaccou · 

matter, t hat will id:o rc ·ci v .- P<L rate consideration. 

~ .. i.- ustmll y th ·a::; with dacit ·, the g roundma · of tho.-e ro ·Its pr :;cnt.- lt 

11 10 -t r entarkable ya ri ty of -tru ·tur ·, fLn d upo n tb variatio ns in the TOundmass 

most of the di tinctio n.- arc to b ba ·cd. To n. c rutin ext nt thi:; i · t nt of th 

ph nocry::;ts, at lcat>t a: far a · their r clativ abundanc i ·on ·ern cd. po n the 

whole, however. the Crater Lake dacit ·, irre pee i,·c of t he extrom variations in 

the g roun dmas.- a r chara ·tcri zed by the pr of well-d fin d p heno ry · ·. 

Thee minemls ar labm.dori t hyper. tb ne, and brown horn bl nd , all of whi ·h 

arc u ·mt:ll) present, al · augite and olivine. which may oc ·a ·io nally be se n. 

MINERAL COMPONENTS. 

FELD PAll. 

\~ hil phcnocr y. ts of feld ·par are fa irly abundn.nt in all tho.-e da ·itcs a nd in 

!:!O m ·1 eeimcns very numerou indeed, in no ca · eould ortboclat> be d t ct d. 

Not only i · it tr u that the fcld ·pars turn out to be a~Yioc a ·e, b ut plao· io !a.- of a 

decided ha ic m ricty, usually labr ado ri te. In fo rm t h y do n t appear to difl r 

materi ally f rom t h imi la.r phenocrysts in the an de ite ·. T b rc a r to b n comparati,·ely larg , stout crystal' with th basal p inacoid and h rachyp inn,coid, th two 

half pri ·ms, a ncl a n additiona l dome o r I y ramid; also crvstal · that a.re ru rc n a rly 

r ectang ular in ·ro.- · section and usually ·mall r in ;::izc. The ·tout Ty:,; tal · with mor 

elaborate forms ar probably olde r t ha n the othe r ·. at 1 ll:t they app a r to hav 

g r at r extinction a ngl sand to be long t a mo re ba i • p lagiocla . Tbe:>e cry t al.-

ar c usually not numcrou · nough in a ny nc thin sc<.:tion to a ll w th accurate 

determinatio n of t he maximum extin ction ang l s: th extin tio n a ng le::; g i,· n hel w 

tb refo r , althoug h they a re tb max im um oh,f'lTcd, pr obably do not indi ·ate feldspa r.- as ba ic a · tho ·c a t ually pre;,;ent. e ·t io n · cut pcrpendieul ar to the twinning 

pla n a nd th rofor ·bowing symm tri ·al extinction,; , o·av th e following maximum 

extinction a ngles Yi z: 30° in No. 101,31° in o. 10±, 30° in No. 1. 7, and 33° in r o. 103. 

All four of the.-e spccim n · cam ' from the dac ite f Llao Ro ·k. o. 101 i::; a ,·itrophy ric dacite f rom the soutb m edg of t h fl.ow, a nd is n.lmost id ntieal with Xo. 102 

of whi ·h a ch mica! ana ly: i.- will be fo und o n page HO. No. 104 it> a ·p heruli tic 

m ri ' ty of a vitrophyric typ a nd Nos. 197 and 103 ar approximately bolo ·ry tallin typ -•·. The c meas uremcnt · indi catca. plagiocla.-eat leatas basicas la bntdo ri te, 

a nd probably more , o. Th above extinctio n;:: rf'pre.- nt, howev r not the whole 

l'I',\'Sk'l.l, hu t tb inn •r part. Thf' outer shell oft n g iv .- mt teb sma ller a ngle,.,. For 

i nstan(·e in ('\ o. 101 tlH' Jn:u·g·i 11 ,,.i V<'s a n cxti nttion :wglc of 2-:1-0 , which .i .- six degr ee.-
DA OITES. 101 

I ~s than at the center. but \ en thi i not too . mall an xtinction for la.bradorite. 

The mea urements o·i ven for the plag-ioela, ·c pbcno ·ry.·ts of he Ll:t Rock tlo'>'· do 

not differ materially f rom the oh ·erv d xtinction angl · in th other da ·it ma " C;' . 

Zonal structur i · very strongly d velop d in tbesr larg-er I lftgiorlasc I h no-

·ry.'t:-:, and is patti ularly con ·pi ·uou:; in . ctions ut appr oximately parall 1 to 

the bracby pinacoid. In . uch ·cction. tb 7.0nal banding, as ·e n in I olariz d 

lig ht, indicat that tb crystal. in the earlier .taO' . of g row b bad ·impl er 

form'- For in ·tance, in a .· rti on parallel to the bra ·hypinacoid .·bowin g xt rnally trac of th ba ' al pinacoid pri ·m, and two dom · th c ntral or :;bow.· 

only the ba al pi nacoid and on of the dom s almost at r ig ht ang lrs t th , firRtnam d form. In .-uch .- cti ons th e zon f differ nt xtincti n · usually . had 

g radually into each o~ , so that from th ent r ontwa.rd the xtinction angle 

become. l · · and le. ob liqu to th tra 'e of th e baa,] pinacoid. \Jmost ahvay , 

howev r, ther e arc to b ·een one or more quit i" harply defined hell with ratb r 

abrupt differ ence in extinction. Furth rmor e. this abrup n s:-: of change from on 

!>hell to the n xt i: not infrequently ac entuatccl 1 .r the fact that the cxtin tion · 

do not chang regularly from the ente r outward. but oscillatf' mor r 1 s:;. ]n 

oth r words, the plagiocla · con. ·i.· ts of conce ntri c ;;hell ·· that alt rna.tc b twe n 

les. acid and ·more acid feld par. . A ' far a· obse n ·ecl, th actual ce nte r i nea.rly 

always th 111 0 t ba. ic po rt ion f th f ld par but th ·bell immediately ·urroundin o· thi. C'E' ntcr may h m rc ncid than the n0xt u · ed ing on . Tb altcrna.-

tion of mor and I ,:; acid sh 11.· i!:! not tt. ·mtlly . harp nouo·h to admit of po.-itiv 

11 1 nsurem nt. In th two following ·a, s th - measur ments wer ·harp enough 

to ju:tify r ording . 

In o. 102 oc ur :1 ' ction f plngiocla · that is cut approxima tely parallel 

to th brach} pina id and that show:; th altrrnation of 7.0nal ·b ]J·· ,. ry clearly. 

This may b · en illu tl·ated in fio·. Fof Pl. XlV (p. 76). Th three mo.-t con ·p icuon · zon ~ are mark d 1, ... , and 3, fr l1l th <: ntcr outYI7 ard. The ry."tal form:; 

that ou ld br identi1i d hy mea n:; of th e cleayao·c cracks a.rc tb haF:al pinacoid 

(001) n.nd the pri ' Ill (110). Two othrr p lao·ioclnR ny ·tals are grown into tbi.- oneon almo ' t at ri o·b t an D']e., to 1 e s n on thr I ft side of tbP f:ig ur ; tb oth r, in 

the u1 p r left ·orncr of tho fi g ure, appear;; almost to continuo tho outlin es of 

the main cry tal. The E' wo cry: ta ls do n t appear to 1 e in twinning r elationship to the oth r. Th xtin 'tion a rw le , a · mea;;urecl to the trace of ba ·al pinac id , a w II a:,: th orre;;pondirw p r ·entag of the anorthite m leC'uk, are gin' n 

h low for the tlu e ;~,on e : 

l = - l 2° = 43 pC'r c nt An = basic a.nd sine. 

2 = - 21° = 53 p r c nt An labradorite. 

13 = - 5° = 30 pC'r <' nt. .\ n = ha c ligoclase 
102 Vl~'l' W tHA PH Y OF CRATE!{ LAKE ATIO A L J:'AR K. 

Th <' percentao·e:'l of An a r g·ive n a~ C'O l'l' ~po in g t.o cxtin c io n n,ng les mea·-

urecl o n a sectio n xadl_,. pflntllel to th hra<"hypinncoid. Thftt thi.· is not quite 

tnt ·of t his section is pro,·ecl by the fa ·t that tht' ang·lc of q ual illumitmtion for 

th thrc' zon . i.' + 21)0 in.·tead ot' the r eq uired <t ng lc of + 3-:1? . A the::; cxtinetion a no·J.,.: do not indicate quite a::; l a. ·ie n, plag·io las' a.· do t h-e extinction angle· 

o n mmetri nl sectio ns, it i prohahlc that a s ttion cnt cxaetlv para ll J to th e 

lwaehypinacoid would o·iv still larger extin (·tion :tng-1 ~ han <trc he n' indieatcd. 

But. at lea:t t he:e mea urementl suffi ce to prov that in this ea~:>c the inn r portio n of the rystal i. not as ba::;i · a: i::; th in ten n d iate zone. 

Tn o. lOl wa.· se n anothe r se t io n of plagio lase, nt Himi la rl r to thi;;; onC', 

n.nd a lso s how ing simila r extin ctions. Lilt ' th - c xantpl o·i ve n ;dwv , 1 is the 

c nt r and ± th mfL rg·i n. 

1 = - 22° = labradorite. 

2 = - 14° = b~i c ancle. ine. 

3 = - 16° = ba ·ic <ende, in . 

4 = - 1\ 0 = I a iC' olig Ia <'. 

A compari. o n of th r Pfr a. tiv po' e r:; of th plagioclase ph nocr y. t: in th 

r ·k. c·ont<tining th se tw cry tt1l. : how: that th y hav hio-h r rcfl-active power 

than ha.- the adjac nt 8anada ual·am, i. e ., high r than L. 540. Thi.- wou ld . indi -

cn.t.c t hat th y an' mon" lmsie t ha n oligocla e, <'Vt' n at tb dg . o:f th e ·rysta l. 

The plag·ioclasc ph noc ryst,; lLl'C f req uently hrokPn ancl th frag·tn nt '-~ ~cattered 

through th g la:,;y g ro uncl1nas ·. Th _v al::;o show frcqu n conosion hut. unlike 

t hr a ndesiti plag io la:es th y do not often r·onta in abundant g la:: in cln ions: nt 

lea ·t, the ·row linu· w ith o·la:: inclu. io n.-: ltnd their di,;tribution in an int rm d iatc 

zon is not ·baract ri -tie. An xeeption mu ·t be tak e n to this tat m nt, ho we ,·e r 

1n fft\·or of tb dark-colored ·ecr ction.-; that r ec i,· :pecial trcatnt nt furthrr o n 

in tbe pages. In lusiont> of ·lend r apatitC' n d l ::; are ommo n; a.l o zircon 

cr. tal.· in :hort colorles · o r li o·htly hrown i:-;h pri ms may h seen, but ,·ery 

pa ri n ·l_v. 

Th p lagiocla · t hat helongs mo re partic- ularly to the gron ndmas · scrms to 

he o ligoc· las , on account of th r ,-e ry ,;mall ext inction angleR. \. mor<' detai led 

dC'seription of t he g ron ndma:s f ld:-;pars will he fo und in co nne ction with th0 

descriptio n of tho dift rent dacite tl ows. 

Ortlw ·lase Lnd q_IW?'Iz arc al. o entirely ('On fin ed to th e oTo undma · · a nd will hC' 

dis ut>.' d later. T,·idymlte is not common. It oec·ur: in the cnstomary elu t rs, 

appar ntly fi lling- snmLI ·avitie (121)· also to some ex tent in t he flui dally a r mng·ed 

lithoidal clac i.t ' . 

HORNJ3LE~DE. 

Tbi::J i · a very characteri tic ingr chent of t he C ra.ter La], dacite. . While it i: 

aJmost ntire ly wanting in th twde:ite., it i.- con: pi cuou.- ly pr ·ent, althoug h in 
DA l'J~8 . 103 

on ly o ·a.·io nal ·ry:;taL, in t ht' dacites, or. :tt lea 't. in lllo:-;t of them. Out of Lwentyc ig-ht. thin scetion s prcp<tr tl from d i tl'en' n t rock . ·p<'c im ' ns l10rn hl encll' could h 

found in all but Jiv . Tr11c, it i.· to he s • ' n in :t few of tlw t,hin sel·tion,; in n•ry 

small Cr j ·tais fl. nU in none of th ' ro ·k . doc:; it HSSUnl ' :t prOl1linPnt ro le a,; fa r as 

qunntity is eo nc rn cd , but it ir,; alwa.\·s ,·c ry ea ·ily n' c u·ni zecl hy its p culiar ·olor 

and ·haraetc ri.sti pl cochroi,·m. (t occ urs alwn,y:-; in long sh' nclc r prism;;, sen ' ral to 

many t imes as lo ng a.' thick. The pri. m irwari:tbly <lnd .-omctinws also ton slight 

extent th<' tlin opinacoid is ::> trono·l.'· and .. harply clc\'('lOI d. Terminal fa ·es are 

oft n wanting, nn l wh e n present appear to he th e u:;twl fhtt h;ts;tl or pyramidal 

face.-. They are fr £tucntly rninutP and arc rar ly ,. r l. i) lllillirnct' r:; in length. 

The. e born blonde may a ll be classifi ed a.- bel rr g i ng to th brown \'arirty . n lthouo-h 

th .rr i. r ally a gr at rarwe in color. They may b e fu rth r r dividrd into. first. 

browni. b-oT n ; and . econd, b rowni.-h-red Yarieti . . 

Tho fir.-t., or brownish-green hornbl nd , is much mor e c-ommon than is th 

. econcl variety. Jt may he , t udied in No ·. 10:., 117. and 11 ' . .Piro hroi.-m is ry 

. trong. ( = dark olive g ree n with usually n, trac of hrown. b = d11.rk g-rcr ni;;: h 

I rown , '\ = lemon ·'· ell ow to gTe ni::; h yrll0\"1'. \..t timr · t he ray. vibratinrr parall el 

to .c n.r almo t n purr de p oli ,.r g reen. 1 n any r 1·e nt brown is m o ,t ·on ·pi ctt ou" 

in th ray. Yibrating paralle l to :b. Thi · hornbl ndC' bas a Yery unu"unl ah o1·ption, 

in that th<' ab ·orpLion parallel to b i · g r eat r than that pill·all 1 to .(, tints, 1' ( a. 

J n ·om <lSC" th r appear · to b ,. ry little di fi'e rencr in color a nd absorption 

l t\\'C'Cn b and .c, but' h r ever th rc i · a mMked difl' r nee tb ab' orpt ion i.· a 

g i,·c n abo\·C'. Profe ·or R o · nb uscb " r f r t an b. n ·ation by A. 0 ·ann of a 

hor nbl nd phcno ryst in a n and ·itc from Ho,vazo, n.ho d e Gn.ta, which ba · not 

only thr 'll lllC' ab · rption but a l,;o nra rly th e .'atn c color ' a::; ha,·e tbe ' c hombl ndc 

pbenocr y -ts from rat r L <L kc. The pic ·hr i rn a.- g;i,·cn i a,; follows: a , li o·ht 

g r ce ni.' h y ellow; .b g r ni.- b b rown: c, dark g rc ni~h y !low: a nd b > ( '\. 

Th extinction ang-le· fo r th :-:e h rnblrnde ny ta l:- ar 1·e ry ·mall , 6c or 7° 

beitw the max imum ob CtTrd. FurtbeT optical pr p crtic ·, a · far as onld h 

ohs rTecl , a.ppe,tr to co rTe;' p ncl " ·ith tho r of t he similar hornbl ende th;tt forrlls a 

largr lXLrt o f som o f t hr Ho-callr d sec retionH to be de ' crihed la ter in thi~ p<tprr. 

Twinnirw pamll I to tlw o rt hopinacoid is Ycry common. 

Tb dark bro wn U1-red yaricty of horn b l nell' is t be :c n in No . 104, 11 , 

lL, ancl lH· it also occur: le:-< s :riHtndantly c l ' ewhe r · . In form it do · not diffe r 

from th e ahove-dcscril eel nnic•ty. Tir e plcoc hroi m i · fu lly a:-< marked , but tbe 

colo rs arc ,. l'Y l itforent .c = lark hrowni ·h r d b = r cldisb brown. n = y ell ow. 

with .c> 1' >a.. Th · nb. orption is normal. Tbe d p hrownish-r d col r of th e 

ray · \ ihmting I arall l to .( arc ,. ry :;triking and ebara tcri ti c. This co lo r ·is 
104 PF.TROGRAPHY OF RATER LAKE NA'l'TONAL ]>ARK. 

ometime. n,lmo:t blood r d and r mind one trongly of the c lor of hematite in 

very thin ::;cale: . The extin tion angle doc. not differ materially hom tha of th e 

fir ·t vari ty. 

In on or two ca::;c::; both of the:e vari eties of h rnbl nd may he ~e n in th 

same thin Rection (104). They are I oth of them u ually perf ctly sharply cry tallized and unaltered. Only in rare ca es an a partial resorption with clr,·clopm nt 

of black rim. b noted (12±) and from tb ve ry few ~cctions oh.' eJTPcl , it is not 

po ible to state wh ether both of th Yari tie. may have :-~uch resorption rims. hut 

it appear;; a. though thi::; wer e the ca e. A. far a · can he se n there upp ar · to be 

no difference in the rchttiv ages of the e two va rietie . Tbe.\ ar th young t 

of all the pheno ry ·t.<J. The greeni h-brown variety rt.t lea ·t, contain · in lo. urc · 

of plagiocla e, hyp rsthcne ftn 1 augit . The hornhl nd o ca. ionally app an; with 

other mineral 1n the form of nc::;t. and then i not as apt to occur in . lender 

pri ·m a in mor irregular D"rain . . 

TIYPER 'THEr E . 

Thi mineral i not a abundant a · it i · in the ande ite ·, but it i.' never entirely 

lacking. It occur in the arne form - na,mely, pri. m, two pion oid · and fl at trrminal face ·, in the sam habit and with the ;·am color, pleochroi. m, and inclo ·-

ur · of D"]a · ·, etc., a · it doe. in th e an de itc: . The reader, ther fore is rcfen cd 

to th i .' ription of this mineral a: g i,·cn under th e and ·ites on pp. 7 to '2. 

It could not be noti ed that the pl ochroi m is le pronounced or the color le::;. 

deep than they are in the ande itic hyper thene o that there is no rea on for 

con:idering the e ortho rhombic pyroxene a ' n. tatite rath er than hyper thene. 

The cry tal ar mo tly very ·harp, although th y may at time : hm some rounding of the corner . T n only one case wa · a r e orption noted, accompanied by th e 

d velopment of a dark bla ki ·b-red, opaque rim (112). 

AUGITE. 

Thi mineral i · to be een in ahout one-th ird of the thin . ection tudied. It 

1: much le:s abundant than hyper th ne and is inclined to occu r in more or les.' 

irregular grain: rather than in harp cry: tal , although th latter are by no mean: 

lacking. In color it i a pale green without noti ceable pl eochroi. m. It ha been 

noticed to inclo e mag,netite and apatit . It i }'Otll1g r than hy per:thene and al:o 

as R gen ral thing, younger than plagio lase, but is older than born bi en de. 

OTHER :MI ' J<.mAL . 

Olimilne wa ob. ervcd only in the older. ecr etion: that accompany the ·e dacite-, 

and will b referr d to und r that head. Apatite and z1'·rcon occur a · occasional 
DACI'J'F., . 

inclo ur s 1n the d iffer nt phenoc ry,.;ts, a;; do ,.; a,l,.;o mag n tit<'. Tl1<' tir,.;t of th es<', 

howeYe r. is 11 t ca •ily found. J ts co lor j,.; :-<O IIl tim(',.; a d isti n(·t brown, nnl th • 

form ronndi:·b pri mati c. 

The o rde r of c ry.'tallization fo r tb :tl>o,·c 1nin rnl:. l •;tvi ng· o ut these lctstnamed ac e. sory mi nern,ls, is as fo ll ow,.;: Hyp r::;th n . plagiodas\'. aug ite. and 

hornbl ende, with ::;om varirthility as to th e plag ioela:<<'. n,.; this min <' ml is :I t 

timr,.; oldC'r t hn,n hype rsth ne. 

DISTRIBUTION AND D E SCRIPTION OF DACITE MASS E S . 

LLAO ROCl\ YLO\\' . 

A.· fn,r as may be juuged from the few sp c inJ <' ns voll ect<'d from this mo:-;t ·on -

picuow of th 'mtcr Lake dacit flow ' , th0 Llao Hoc k mas,; s how,.; thn' C' quit<' 

di:-;tinct ntrieti .-. of dacite--namel.,-. ,-itrol hyric, lithoidal. a nd ,.;phern li tic dn ·itr . 

\TI' HO PII Yin(' ll1\ 'ITE. 

Thi. vari ty was 'ollected from the <'xtr me soutb0rn dge of tiJC' lam flow. 

wher e it i. nece. sn,rily Y ry th in. It i: r p resent<'cl hy ::-l os. 101 n, ncl L02. Th hand 

·p im ns prese nt the appen,ran e of a pe rf tly f rc ·h v itrophyr in whi ch th oh s:c: 

ha::>e, which c·o nstitutc ;tt I a t four-fifth s of the ntir<' mRss, has a clark, g reenishg ray ·olor. In tbi · g·la " l a e ar i nrlo:ed nume r u · ph no ·r.Y ' t · of p lno-iod:lsc that 

111 a::mre n t O \' r 1 to 2 millimeters, and tbn,t ar white <tnd g lru ·;;:y nnd show bn,rd ly 

a tra of lea ,·agr. ln a ]clition to th se ar a \'ery fmr minut , deep-hmwn to gree n 

and hla k. r c:;ino ns-lust red cry. tals that are h:u·d l.r to be se n without a mag nifying 

gla ·s <tnd that. in thin s ction, 1 rov to he n ··ually h.\ pc rsthcnc or homhlende. 

Th r a r - a lso to h n ted a f w :uwu lar fnwments, cOJnpact, gray ish brown <Lnd 

du ll lu: te r d m a::;uring on -qun,rte r inch t one in h or more in diam te r. The ·e 

a.r<' r f rrecl to later un d r the h ad of nod ular . cc r etions. This rock is m r e or lc.-.-

cra. krd in difl:' rent di rection:,: owing to ,;hrinkag·e in coo ling. The rock parting 

a lo rw th e crack ' . wh i h ·ometimes gap br ak · into ,·e r.v sm oth fl at surfaces that 

have a d istinct o::~s . Otherwi. th e fractu rC' i ' rath r r ough or ,;nJH,Il- onco ida l, 

owing to th e pre · nc of th abn nd a.nt phgioda,;<' ph no('l'yst..,:; . Thi: Yitroph_rric 

da it m::ty n,l. o b str eak cl h.v more or l ss pamll e l bands of g rayi h-looking pumice, 

as may b s C' n inn pe in1 n co llected by tb writPr on the ,.;nm :-;p t. (No. 2013. 1 

o{ coli c ·tion of H. B. Patton.) 

T n t hin :; t ion the g·lrt "' ba:'c n.ppea rs to b cle:tr and color! s and to h now 1 l 

with v ry . ha rp nnd st ~t gbt rtnd r maxkably evcn-.- izecl mi cro li te ' of aug-ite that 

mea ·ur 0.003 millirn ter wid by 0.0,<1 to 0.0-! millimet r long. ( e fio·. of 

Pl. XVIII p. 132.) Th . e microlite a.r e too .-mall to . bow any e lor but th strong 

refraction i · evident as well a · doubl r 'fnt ·tion and n,n extinction a,ng le up to -1:5° . 
106 P ETlWGH Al'HY OF 'RATER. LAKE .A.TfO AL PARK. 

Th r ar ttl ·o to he :>ccn • 1·cry few upaqu cu LT!'d bin. I· tri ch it '"· Th , ::; tmio·ht, 

colorl e. ·s ;utg itc nti c rolitt'::; app ar to h • th ' sa1n ' <~> e to ht> ,' ' ' n sparinv·ly cl(' l ' lop ' cl 

·~ thi n ·c ·tion prt> par •d by th ' nitr(l 'tate:-; r o lugi ·a l ' ulTCY fron1 t he rh yo li tic 

pe rli t 'of tlw Y llow.t one Nati nal P ark_. " Thy ::; till mor ' ·lo::;c ly r ::; mbl in iz . 

a.ppenxan · ', and nnml cr.· the :-; tra.ight colod c ·:-; n1icrolit ,.; in th e da ·ito from Las ·0n 

Pen,k, (Jn,liforni <t, . R2 of th l'tbovc-m ntioncd ~ lucational e ri li Th ·lo:-;' 

rc,;cmi>Jancc IJ tween th Llno Rock dttcitc and thi.· dn. ·ito from Las. en P 0ak will 

b0 again rrfc rr0d to in the ·c page:;. 

\. f w f clcl .·par minolitcs o 'Clll' in ~o. 101, but almost none in 1 o.l02. The ·c a rc 

in part lath -.'bapcd phtu·i oe la '<' with ,. ry : mall xtin ·tion a.1w l but .n1ainl) sh rtrceta no·ular to syua.rc , un twinn ccl f ldspn,r that u: ual ly xti ngu i:he · " a rl y pamliC'l 

to tbc .'ide·. In No. 101 was .'C n a ncn.rly da. h~ · section of f eld ' PiU' thn,t wa · 

not h~r r than nor cv "a.' larg·e as mnny of th fold. par mi cr lit :,; (0. 5 mil lim tc r 

long), in the e ntc r of which was a brown-gla ·. inclu ·ion with ·ide· pamll l to t he 

cry. tid edge" and occ.upy ing- at 1 :vt one-th ird of th E' whol e ·ry.·tal, it · If in lo ing 

a compn.mtii'Ciy l a.rg a.ir bubble. Tb xtinction ano·l mea ·ur d to th long t 

: icl wa. · 1 °. o tw inning wa. appn nt. A r produ tion of th is I'} !'tal may b 

: en in Ji g. 0 of P l. XIV p . 76. 

F luida l stru ·tn re, whi ch is hardly to be . en in .the band . pe un n 1s ,. ry 

(.;On.'pieuou.-; i n th thin ::; ·tion, owing to tb ' more o r 1 :· paml l l a rrangement 

of thP llli ·r lit c~ whi ch oc·ttll' in li owing lin <' ~ lapping arounJ th e ph cn c ry.t ,; of 

plag iotla. , hyp ""then , nnd bornhl nck and of a ·ces:ory mag net ite and ap ~titr. 

H ) p 'L'.'thcnc is :<:arcc and hornblc>ncl ::; t ill more ·o. Tb latt r o cu r. mninly in 

very ·mall n<'cdlcs ttncl only occa ionall. · in er y:tal " comparable in ize with the 

bypcrstb ne. In n in :; t~tn ce a m~tll ry.' tal of hornblende with ·harp cry ·tal 

form: wa · ob ·en 'ed cl arly inclos d in pla.gi cla · . Thi i:; a, d cid d ex· ption to 

thr rule that hol'llbl ndc in th e: o dnc·ite:; ;,. th youno·e:t of th ph no ry.t · with 

th po:sibl exc ption of an o·i t . 

Th' hcmital analy:i: o l' . 102 J;4 o·11· n on pa.g U O. 

Thi. r o k (103) eom · from th :ummit of Ll a.o H.o k. Tt con ' is · of a lig-htgmy. 1 n · . <tlld s 111 what po rous g roundma:: with thickly s ·attcn•cl , :mall, white 

f eldspar ph noe r,vst: , : imil a r to tho ·e in the vit rophyri · m ri et,r; it l'On. i. ts n.l. ·o of 

a f ew ~t lm o ·t unnoti cefl,bl cla rk r p henocr,\

7 ' . lt h r a.k: with <~ deeidecl ly r oug h 

fmctur and do · not ·· bow an.) fluida l stnictu re. 

In thin . e t io n the g r oundnw ·s i.' ·een to conl:.o'tin sma ll plagiocla e htth , 

'imila r to b ut much morr abundant than tho:c 111 o. 101; 

"No. Gl of thr Erlurnliorml , rri ~o f l<ork<, dc•cribe<l by J. 1'. ldrllngs in Bull . . S. 

bJ . . Dill,•r, op. cit., p. 7. ' 
DA l'P_E, . 107 

ah;o n few feld. par ry:tallit .. with r ct:wgular outlin (\' n11d mu<"h mor frld . .;;p;lthi<' 

matt r that : how·· no di,..tinct f'om1" and that i.· not Ull allr of aiJ lu t\' i(l\'ntilimtwn. 

Th rc ~ undoubtedly mu ·h gla~.- pret<e nL hut, lll'irw <'o lorl esl", it j,.. alnrosL cO IH' 'llit'd 

by th. abundant ny. talline m;Ltt•r in ·lo,; cl. ln white li g-ht with wpak rn:wnifying 

power: the thin ::>retion ha ' a ·on1 ewhat du -ty appL'aranc: ' . \\ hrn strongly mag·-

nifi ed thi · du. ty matter r e' oh·e i ,; If into minute, co] rle s, strai o· ht :wg·itr 

minolit . , like tho e ~ ·cribed .a;; charact ri-ti ·of the vitrophy ri rhyolite, togrtlwr 

wi th some \Yh !Lt larger nritrolite · of thr same n1ineral that in ·lo.-r a f w \' cry 111inut!'. 

l>laek, and opaqu g rain:- prc ··umably of mngn tit . Prob;tbly the dusty ap1 C'H rn.n · is int nsifi d b. th pre: nee f small air lmhhl s in the o-lass ha.-;t'. Plwnocryst · oc ur about a in No . 10:., and 101, with thf' atld iti0n of a \'f'ry liti'IP 

augite in .-harply d fined and almo t · lorle .- cry;·tak 

Thi.- an not h aid to be a . I ic:a l lithoidal dac itf'. Th ;d_mndan ·c of phtgiola ·e mi rolit and the ' car ity of the untwinn d gronndmass frldspar wi t h Hq uar<' 

orr eta rw ular form:-: cau:::e this rode to res mhl(' ,.;omc of th more dncitit ;lndrsil!'s 

of this r g·ion. 

, I'll ER !,1'1'1 (' DA CITE, 

A spe imr n of ·pherulitic dacite, No. J.OH, wa:-: coll ected on Llao Roc·k in .L '83. 

Thf' fipld lnhf' l aceompanyino· th 'P cimen do .- not .tate tit<' cxact lo ·ntion. Jn th f' 

hand spf'<·imell t·his s~ en to cowi t of a nea,rly black glm;. Yery thi kly n wdl d 

with br wnish ·pherulite · hat m a.snr from :i to millim ten; in diametrr. o 

t hi kly crowd d arc th ·· sphC'rulitc:; tha,t lh y often interf r and tnak up mu ·h 

morr than onC'-half of th tn:ct.'s. The spherulites consist of two, ::;ometimes thrPe 

part:;. The t'ntl'l' is of a dnrk-oTay col r. and ha:-: a Yf'ry den -c, fel.·iti · texture. 

round thi · is IL rin o· or zone about a m1llim t•r widf', of a le:; d n e ore,· n of 

minut ly porou ' mat rial , and of a l>rowni:-:h. rccldi, h-hrown. or light grayi h-br wn 

color. Out.c;id f this nga1n occurs u ·ually, but not nhra~ s thC' third part, dEo n"e 

It k th ·en hal p rtion . and either gray in eol r !1 kc the <: .nt r or of n de p r brown 

than the inte rmediat zone. 1lnny of the. ph rulite.- show o·apprn g tratk.- that .-e 111 

to he ('O nfinC'd t th< n1i dd l zonC'. TI1C' rc is how ,·er, no trncc of litlto1 hpnl cl<'v<' lopnt <' nl. The inside of th sc ca vities i:-: rouo·h , ;tnd [ about the same color as tlw 

micld l zo n of thr pheruiltes in \rhich they li e. They do not a1 pear to ·ontain 

erystal . pon ero,;s fractnr the ·c ph <' rulitcs ha,-e a distinct radtated apprn nwe . 

'L'hC' customary phenoc ryst oc ur <] lllte indifferently in the gla ·s.'· I ortion a.- w II as 

in th spherulite.-. 

l nd e r tlw mi cro. cope the o·Ia.-:y g roundma · is almo-t id ntica.ll _, . the sam a 

that of t he vitrophy ri · da ·it de'('l'ibed abo\· . The :-:n m olorle H.ugit mi roli tes 

of a.bout the arne siz , 0.03 to 0.05 millimeter long b 0.003 millimeter wide, rn ay 
10 PETROOHAPRY 0 1•' CRATJm LAKl~ .\TTO N"AL P RK. 

b .· en. \. vcrv sli o·ht diMinction may h noted in that thcsc nuo·itci mi crolites a.r . 0 .., . 

not perfeetly clear hut often han; it ~ma,ll atllount o£ b lack, opaq ue <lu ·ty matterprobH.bly mao·n ctite- c ith r adh ering to th outside o r indo: d within. Cun- d, 

hlack mi cro litc;; w' r not obst> rvecl. Mo..;t of th ~]Jhcru li tes : bow two or t hree 

period of gTowth that ('O LT :pond to the differ nt colored 11 nc~ n ti cable in the 

hrwd :>pecimen. On r two appear to bfi.Y hfl.d but on p ri od of g rowth- that 

co t-r c~pond in g to the inner portion of the other ·. Thi:> inn r part ha: a di rty-brown 

or g ray i,;h-brown color, let" th rough hut littl e light, H.nd . how" a d i ti'nctly fibrou " 

rad ifl.ting structur . The fibers a.r \'C ry f:in and ba.rdly di ·tinguisha.blc from 0ach 

other. They pola ri?.c light f ee bly, fl.nd haxc ~t positi,-e cxten ·ion. Owing t th 

partial opacity of th i: entra.l 1 ortion , the u. ual bla k ros. i hardly di:c rnibl e. 

The portion of th e ·ph rulites that b ong~ to tb0 · eond r int rm l iate z ne 

doe: not .·e 111 to he a porou." a · th e rather rough appea.rHnce in th hand "P imen 

would indicate. It i , in :fact, 1110 tly quite s li d. lt appe11r · in }L light-brown color, 

very much lighter than the central part, and i: compo. de " ntial ly of <li . tinct shred: 

of a olorle. · min ral diverging f rom the c nter outward an 1 bran bing at low angles. 

The ·hreds a,rc coar "c en ugh to show xtiu tion nngle · oft n quite obliqu to th eir 

longer axe. . They hav invariably a. I o itive xtcn ·ion. In po lariz d light they 

app a,r to continue tb' finer fiber:> o:f the c ntral porti n. Between th a.rm of th 

br:tncb ing po itive bred.· ccuroj fr qu -ntly u ni nd ivid nn l ized mntter that ' how fee hl_v 

11 u·ati v · polari:.mLion- ·ousille ri ng thi: s11 b : L;w(·C Lo 1..> abo fibrous; but all th mor 

di: tin ctly r cognizal)lc . hr ],.; ar positi,·c. 

The, e coan;c bmn ·bitw . br ds so Jo,..ely con ·pond to the feldspa r of the sph rulitc · in the obsidian of Ob. idian lift in th Y !low ·ton Nntional Park a: d ·crib · 

by Iddino· .,a and to tha,t of th sph ruli tc' from the r egion of Ro ilx'L and ilver Cliff, 

Cu ter County ol . , a. de ·crib d by ro: -,b that, after ··tudying thin . ection pr -

pa.red from : ph rulitc:· :from th latt r pla c, the writ r ha · no h itan cy in p ronouncing the e in th Llao Rock dacite a. belo nging to :fcld ·par ~d so . In th ir po:iti,·e 

cha.ra ·ter th _v on e. p nd to th fold. par in manJ of tb :ph rulite. :from u. ter 

' unty , C lo. Tb brown isb '·olor of thi int rmediate portion is du to the pre -

n··e of hrown, y llowi. h , and r deli ·h :ferritic mntter in the form o:f clu t particle , 

and o ·ca. iomtlly in the form of minut ·cales. A rad ial ~trra.ngem nt of thi: ferriti c 

111 att r i. not mark ]. 

The out r portion o:f the e :pherulit ._: when seen in bin . ctions appea,rs to be 

i lenti al with th ·cntral cor . Jt i. often cntir0l_y mis. ing, and wh en present doe: 

not usuall r envelop the whole ·ph ru lite, but app ars a: irregular lob or prolongationoj of th e , amc. 

~ C'n ~tit11tlon and origi n of ph naaJt C~ 111 ncid eruptive roC'k:-t: B1al l. Phil o~ . Soc. \\",lshing tOJI , Vol. XI , 1 91, pp. 411-440. 
DA l'l'ES. lllV 

The ·tring::; of auo·ite mi crolite: that a,cc ntu:ctte th fluidal stru dur of the <>'htssy 

pa rt of the ro ·k pa '· uninte rruptedly through th ·c ·phemlitc .. , a nd th ph 'no -rysts 

lie emb deled in them as well as in th e r emainder of th e r o ·k a .. i uni1·crs1tlly th 

ta.. in ·uch bo Ee . Part of th e f rritic matt r may be ce n to a ris front th furtb 'l' 

oxichtion or hyd ration of th ore parti cle .. th:tt ad her to th rw gitc mi cro lit :-;. 

The ph nocry ·ts observed in this roek ar plag iocla ·c hyprr tb nr . homhlcndc 

<tnd aug ite, with acce. sory apatite and mag n tite. Th order of c ry .. talli 7.ation i · 

(1) mag ne it a nd apati te, (2) plagiocla:e, (3) h rpersthrnc, (±) augitl' an ] h rnbl nd , 

(5) the spheruliti e fo rms: to whi ch may be add c1 nugitc an] felcl .. par mi cr li t s f th 

g roundmas., which l elong betw en± a nd . The hornbl encl i Yery ' paringly cl ~ loped, R · i · ~:> ual, b ut o ·curs in both the IJrowni ·h-g r en and in th brown i b-re] 

,·ari eti e . 

Thi · pheruliti dacite hould be compared with the Yery irnilar o cunene .. in 

the Cloud Cap flow. 

In th t hin ection f thi .. r o k may al o be . n a few ::;mall inclusion" of 

identical natur with th in ·lu ion· of older ·ecr tio n · to b fou nd in No. 10:6 

d ·cribed immediat ly below. 

:XODOLAR SECRETI O:XS. 

In the description of the v itr ophyric dacite (102) f rom the outh end of th 

Llao Rock flow, refer ence i. mad to inclo d angular fragm nt · of compact. 

grayi ·h-lr wn , dull-lu terecl material. In th thin ::;ection of thi.' roc k tbcr 

o cur tine of th s inclu. ion · th large .. t of which is about 6 millim t -r in diarnt cr. Th y ar compo eel of a loo ely felted ma. · of !::> l nlcr horn blend pri ·m and 

also of nlmo · equally sl nde r p lagio lnse lath .. with tt few o ·tabedron · f magnctit . 

In th int r -tic · f thi.' felt i:; to be .'e n lt b rown g la .,. that c:ompo ·e ' a t mo.'t 

on -quart r of th ma>< . 'l'b ho rn bl nde and plagi oda:; arc pn' ·ent in about 

eq ua l alllountl:>. The horn bl ncl is very un iformly about 0.1 millimete r in width 

and from 0.5 to 1 mi ll imeter in l noth · th pla,giocla ·c i::; about ·th same in width 

hut not quite ;;o lotw. In one of th · in lusions the <'Oior and pleochroi m of 

th horn blende lU' a,lmo ·t icl ntiea.ll.r the sam as that of th r eddi: h-brown 

h rn hl ndc tlhtt is m ntionccl ,tl 01· a · occuning in many of the da,cit . It i:; 

to b di tin<, ui~h d only by th ,·cr.r I nder fo rm and by i >< g r at almudanc . 

Tb xtin ·tion ano·le · in th pri:;m zon a r ,·cry small, ra,r ly 01· t 3° . 

ln anotb 1' f th . in clu ·i ll.' the h rnul ndc ha ' the color and pleocbroi 'Ill 

of tb gT nish-brown hornbl nd of th cia itc ' , whil in th third one the color 

j,.; intermediate IJ tween tbr two. Th i. eha,ng• of olo r on e ponling a- it doc ' 

to tb variations of co lor of t;he ho rnb lende in the differ ent; clacitC's 01· in th ~a m<' 

da ite, t'orrn:-: o n • of Lh • Mgnm nts in fax or of Lhis h ing an old •r <'rC't n. TIH· 

fo rm of this hornbl •ndc d OL'S not I'Hry with thr <·hangc of ·olor. U:-:nally on ly till' 
l]t} l'Kl'IW ' RAJ>IJY OJ!' l~ATER Tu \ KE NATLUN".AL l' ~K. 

unit pri.·n1 i: to be noted. Tb c torlllination" an' not oftl' ll " IHtrp. Thl' pr1:-; 111 " 

·ith ' I' taper out at tin• ' ncl , or •nd r 1wbly , a · 't houg h broke n off. 

Th phwiocla. ·n is tL ·ually s'in1pl,v twinn cl, whh onl y two o r three bands vi,.,ih lc. 

The larg st l'Xtin ction in n "Yll1111Ctrica l ·cctio n ohsCJTC l wn · ~0 . These v ' I',)' 

,; lt•nd ' r laths cont<lin lono· brown cr!ass in ·lo:urc: ~bat often show t he for 111 of t he 

ho:t. 'I' he pri:-;111 ,.; of Iiagiocla:-: and horn bl nd ' do not ofte n i 11 tor fe r ' . hu t w IH•n 

tlwy do it do<'" not ap1 car t\1<tt o n of t he· ' ing redien · i.-; older than t ho othe r. 

[n addition to th o· lath - ·hap d plagio ·Ia · thi, mi·ncm1 also o 'l: lll'S in two or thn•c 

·o1npamti,·c ly large and d cided l_,. ;;pong·iform stout ·ry ;;tnls tb;tt contain n111 ·h 

colorlc,;s g·la::;.·. and bits of ho rnhl0ndo of the : an1e ·olor a::; in th e :0ct io n out,.,idc 

o E the f ' lcbpar. It is mlht•r l'C' nHirkahlc th::tt th i,; 111 i 11 nd Hhou ld h r th u:-; lll(']o;;cd 

in the p lag io ·la;;c, ina ·much as c l: cwh cr c in h<•s' dacite · hornblende IJe long s to 

t h0 y ou ng ·t o f th pb <' noc:ry><t . It i;; to he not rl, however, that, a.· it o 'l'lll'" 

tbu;· in lo ·eel in plagio l~t :-w, it doc::; not hu,-' th ::;amc sharp fo nn a:::; i. ot hc rwi;;e 

to be : CCII . In fact, it prese nt.-; ' Xfl ·tly th o app antnc: ' of having been for 111 d a: 

a sc ondary 111inPral in th e fe ld ·pa r. 

Both hypc r.-tb no and aug·it :e ' 111 to be mis. in,,;. 

The re doe not appear t tb writ r to b much doubt that th .' 1n lo;; urC':-: urP 

fragments of older ·e r tion::; from the daciti . 111f\O'Illa. ftlthotwh th absenc ol' th o 

pyroxene.-; is bard to xplain on tb i · uppo ·ition. Bu t th te nd •nc· r fo r til' ing- rcli cnt: to us.-umc lono· .-1 ncl 'r form.- , quite di , t in ·t from th o: in th ro k in whil'b 

tb y occ ur appear · to b ,. ry cbara tc ri ·ti c n t. on ly of tbi · hut of other .- n etion::; that will I> ' de ·cribcd late r a::; o · ·urring in the dacite ·, and al. o of . ocr •tions 

in tb a nd sit . . 

Fig . • l f Pl. X \ IH (p. 132) i · a pltotomic roo-raph from No. 10.., and s hows 

hotb the sc ·r ti on and the inclosing vitroph ri ·dacite. 

Rcfc rcnct' i,; made c l:,:;c \\·be re to the r " mblan ·e betwt' n " m of the v itrophyri · dacit · of Cmte r Lake and th ' dacite f rom La:scn I ak 'alifornia of 

' bich Mr. Dille r ha · g i,·cn a hri ef d · ·ription. " In this d · ription Mr. Dill e r 

m ntion: ~tnd gi ,-es a I h t gmp h of angu lar nodul · in ·lo eel in the dac it . His 

d ·cript.ion of th e mi cr scopi c app amn cc of tbcs inclu ·ion ·, ·onoboratcd hy 

study of tbc thin .-cction: kindly lmtn d th e writ r for th e purpo:-:e, d i;; ·loses a 

,. •r_y clo: r sembl a nce to th inclusio n: frol)l the Llao Rock dacit •. ln co lo r. 

l'or111 and truc:tural r e lation ·hips of th e horn bl ·ndo lllld in t he oceun 'IH'C of plag·iocla.-c and a small an1ount of brown glass th r '"em b lanco is very dos ·. 'l'h <· 

lllain po in t of diffc rPnec arc tb 0 ·c that th e La "On P0::tk indu.-ion is •o:u·sc r 

grain d, the horn b lcnck prism: arc not s<J slcnd •r, ::tnd t b hornbk ndc not infn•-

C{IIt' ntly i. nclost> s p lag·iocla;;c· latl1>' ; also IJ iotiLc ;tlll1 py r XCIH' and a littl • o livint' 
DA 'lTE, . 111 

and triclyrnit arc pn·.·cnt. The appeamnnl of' IJiotit in tlw La.-;,; •n 1' ak ~' ·rctio n 

i::; to u ex pe ·tecl . a.· tb• same min •ml OTur: in the l:tcit ' it:sclf. 

O RO ' E llTLL FLOW. 

The four ,.;peu rn cns coli ' ·ted horn this mass ( LU5. 106. 107. and lOK) an far 

l'rolll bei ng :t typical da itc. If thi . wrr• the only CXalllpl e or thi:-; kind or rock 

in con n d ion with th 'mt l' Lak lavns the rock w uld nutumlly lw l'IHssilit•d 

a,.; an andesite. A a matt t· of f;u·t it pa rtak e~ of tiH' dmm t risties of IJOth dnl'itL's 

and and >.-:ites to such an xtcnt a: to represent :t tho roughly intl'rllll'diat typt' . 

Tak •n in ·onncction with both th e and c:-:ites and th e dacite:; of the )o;tlrrou nding 

region the uaeiti chant ·te ri.ti ·. I rcdomimttc. :;o that the ro ·k may " ·ell he call da n 

anue)oiitie da it . 

Th ' 8 four ·pe ·imen. a r li g-ht g-ray or, in the ·a:e of :\o. 107. brown and g-ra.1· 

streaked. roug h-fracturing a nd ·lightly porous rol'k:o; with thr usu;tl smal l and noL 

,. ry con:-; pi cuou.- pbcnocry;; t ·. l ' nder tb m c. ro~c op the .!.trotiiHlmass ntrit•s front 

g la ·.·y to hy pocry:;ta ll ine. th > mriati on: ccmring in irregular streak,; to he seen in 

th : a me thin seeti 11. ln gcn ra l the g roun l11ta :-: ontains a g-ood deal of ry:;talli nt' 

nmtte r whi ·b ·on ·i't:; mainly of ,;m;Lll lath-like mi •rolite,; of plag io ·Ia ·c. togrthe r 

ll'ith : mall. r ·tang nlar, untwinneu f ldspar cry ·talli tcs, ·ucb as u to he found 1·er.\' 

:ti>Unclantly in the ntor typical dacite . Tb p lug io Ia c rnierolites ar ' sirni lar to 

tltos ::;ccn in tfr c dacite of U ao Ro k hut ar' hrr much more 1111111 rou" and ar' tit' 

k atur that most ·los(•iy reminds (Ill of tb 'ande::; itc::;. Th y a r ' probabl.1· oligoda;; '. 

a: h ' •xtin ·tion nng l s ar rno ·t ly 1·ery small. In add iti n to thc::>c felch;par.· 111 ay 

al,.;o he ·c n ,·cry ·lende r and minute olorlcs,; mic roli tc · r 'scmbling the auo·it 

rnicr li t : of the Llao H.oek tlow but cl iff ritw in b ino- not quit' :o shaq or :;tra iu·ht, 

a l,.;o in ha,·ing fL tcnut' ne.v to tap r out <lt the end. Th y ar undoubt dly ft.ugit •. 

A ·mall am unt of black, opaque, iron oxide, di.' tributed as minut '. du,.. t-lik I ttrti ·lc:-; , 

a ·:;i:;tl; the augit ntitrolit •:-; in gi,·in•,. to tht gr undma::;s :t ·louded a: pcct. The 

brown olor of ~o. l\17 i,; produ eel hy th e pre ence of brownish a rH1 yellowish 

ferriti ::; tninirw matt r. 

\.II fou r of th ·(' :;pecimcn,.; l'ontain plagioclase, bypc.r:;thene, augite. and r ddi:;llhrown ·hornhlc. ndt' as phenocry.t-;. Th plagioclase has a ,..:trorwc r tende ncy than i: 

eu,.;tornar.l· in th e 'nttcr Lake da ·ite:-; to bce0111!' erowdccl with g lass in ·lusions. 

\ugitc i,.; ntor ahurHlant than in the mor t.ypita l dacite::;. It o<· ' lll" both in : harp 

hut ,;rna!! and ofte n tw inned <: ry:-;ta l,.; and in il'l' g ula r grains. The horniJl nde, which 

belong: to the nddi.- h-urown nr rirty , i.' also ·omewhat mor abundan t thnn u:ual. 

In No. L()(i it' <H·<·urs in ttn c·o rTociPd crystals. on orH' of which thl' forms (lun. (OW), 

:t!td ( 1011) wt' I'C notin' d. In the othpr,; t h!' hornld .nd(• i,..: nH>n' or lc,.;s ro rrodrd and 

ha:-:dcl'l· lopt'd rc:surption rirn,.;of ntagttl•tit ea nd :t11g ite. In F'ig·. // of Pl. X I \' (p. iii) 

may he ::;c n a reproduction of;\ ·ry ·tal of hornhlcndt' in o. ln . 
l l :t I'ETI:WG J:Ul'H Y OJ<' RATE L{ L AKE NATIO AL l'ARK. 

LEBTWOOD COVE l!'LOW . 

This ma:;,; is on of t hr httest !ant liow · to be fo und o n tb nnr of t h 

eratN. cco rd ing to "\lr. Dillr r n pttrt of thi!:! . t rcam was tlu nt nt tb c time th e 

summi t f Mount ~laz 1111 a .· uh ·id c!, a nd <.l po rtion of the ;:;tr cn.m that ran b<t·k 

in to the ]Ji t formed by the ·ub id ing cone 111 ay h SC n at th h ad of the <:0 \' 

at tit water',; edge. The Ja,·a of t his ma,;;,;, <ts far a.· may b juog cl f rom th e 

fi,· : pecim n,; collected. i: of two n tri tie · a ,·itrophyri c ftn d : li o·htly : phc ruliti 

and a. li thoidal vari ty. 

Th e vitrophy ric type i · :eon in o:s. 109. 110. <tnd lll, which were co llrct d 

on th re:t of th e rim. The ·c ftpp <tr in the ha nd : p cimens to h ,, ry g-la;,;:y 

a nd to ·on: i:t of mixture · of black to gra.'·i ·h-bla ·k a nd of r d !ish-brown o·la." . 

Th r ddish-brown portion i · a littl e more abundant tha n th · b la ck anu fo rm:-; 

more o r Ie-· · c ntinuou: ·tr a le, whit th black is mo r 'freq u ntly in tb fo rm 

of small, ang ul ar patch :,; in ·lo:cd in thr fo rm r. \Yhe n cxamin d wi t h a poe!i: t 

magnifying gla. the brown p ortions appear often porou: a nd po;,; ·e. · a somewhat r opy structure, while the black p rtions a rc olid. mall ph n ·r y t.. of 

whi t g la :y-looking plagiocla c aboun d a · U;' ua l. 

In thin :cction it is ev ident that tb br owni. It p ortions re.·td t f rom th a lteration of the bla k g la · · simp]·'' b.'· a proce: of hydration of the iro n conk'tin d in 

the gla s. The f ro ·b a nd una lt r d parts appea r in a thin . actio n a,; a li o·ht-br own 

o· la,·s. perfectl y fresh and cl ar, but irT cg ul trl y d ttcd wi th ,. ry ~-; ll olorl ss 

<Y la:: . pots. This ligbt-b r wn g lass contains ~u e ·s mi nute and colorl e:s aug ite 

mi cro] it : ' bir· h in . 109. ar identically lik tho · in the o·Ia::,;y dacite f rom 

the :outh rn end of Llao Rock. ln No. 111 tb uToundma · · co ntain: in addition 

to the· augit microlitc , also a f w plao·iocla:c micr olites. ln No. llO the augite 

111 ieroli tc ' ar mor slender a nd lon<Ycr, as well a:-: mor ' numerous, and th fe ldspar 

mi ·rolitc · O<.;Cur in lath- ·baped plagio ·hi ' , a nd ·till mo re ·on ·pi ·uously in th l· 

squa ri h or r <:tang ul a r un twinn d fo rm>; that ar mor c ·pccially cbaract ri ti t o'f 

dacite ·. ln all thr c of the ·c t h r· i · a pa rtial cleYelopm nt of ·ph ruJ;ti · fo rm>' . 

The'> o ·cur in : ma ll r ddi: h to brownish or y llowisb ph r e · that v r y faintly 

pola riz lig ht and ha'"' a no ve ry el i ·tinct r ad ia l stru ·tun'. 

Thr brown co lor of the ro ·k a · een in th ' hand : p imen i>; cl u la rgely to t l1 r 

f rriti · n1 attc r contained in tb .: phcrulitcs, but i · a l ·o d u to ·ta ining- of th e g las: 

in th ,·icinit.r of eracb a nd por ,; a nd a round tb sph ruli tc><. 

The phcno ·ryst. , wit h tb exception of plag ioclase, a rc small and ,·cry ;,; ·ar c . 

They con: i:t of h.} per:-;tbene a nd n ,·cry fpw minut r edd i:;h-brown bom b! nd e (not 

111 0rC' than thrr o r fo ur in a thin ;:;c tion). A ug·itC' iR entire ly wa nting. 

ThC' lithoidal vari ty of uaeitC' from this htva fl ow i.o; :;cen in o . 112 ·and 113. 

Th form 'l' ba: a dark-g ray, compact, and d ull-!u:;tercd g roundma · nnd :;tronglj 
.. 

D.A ITE . 113 

developed fluidal structure; the latter i.· light gray a nd lu ter e~ · b ut not fluidall y 

de1relop d: Both of the ·e probably cont.c'tin con id rabl gla , but in No. 112 this 

i partially . and in No. 113 almo' t entirely, ol . cured by d vitrification produc 

ommon to lithoidal da ite . In both, th augite microlite abound, but in No. 11: 

thc:c n.r notftb!_,. larger than in th other da ite.- her t fore de -crib d in the:; pag ::; 

lLnd they ar granul ated b · m an' of ad b ring and inclo. cd mn.o· n tit oTain . In 

thi.- r ock, too th colorle · · c r.r tftlline materiaL of the grou ndma s i · oar er tha.n 

u ·ual. V ry little of it ·an actuall. b identifi d n I lagiorla ·c mierolit . It coni ts, rather, of allotriomorph ic bred that may be feld par or qua,rtz, and that hav 

a general clong<Ltion parall l to the fluidal plan of the rock. ' mall plagiocla ·e 

pbenocry abound, but other phcno ry -t ar very ' car . H o rnbl nde i nearly 

mi ing a nd augi e entirely o. 

A ch mica] anal.)1 i of No. 113 will be found on page HO. 

WINEGL A FLOW. 

Thi embraces only the small da ·itc tl w about three-quarter of a mile long, 

that t.-'1r near the rim a the Winegla ·. and xtcnd.- northea.-tward. In th hand 

pe imen the roc!r (11±) clo ely r e emble · th b rown and !lack vitropbyri dacit 

fron 1 the Cleetwo d ' ve r o-ion. just al ov de Tib d. In tbi. cH.:e bow c r 

the hlack g la · y portion appear more as longatcd streaks accentuatino· th fluidal 

·lructure. 

nd r th mi r o cop th dark r p rtion · that appear black in th . hand 

"I cim n ar ccn to b ompo cd of n ni-l pure ght. s, but not of a uniform color. 

Th rock on ist." of mor e r less parallel trand ·· of ab olu tcly ('01 rl e~ . o·la . and 

f gla ... r ndrred more r 1 " opaqne by m ans of b la ki ·h to browni, h minute t 

du -t-Jik particle · of uncertain characte r. Tb u ·ual microli te of augit app ar· 

to b mt s1ng. Thi intern· avino· of colorle and dark- lored tt·a nd - canse the 

gla to a · ' Lllll a d ·ided tringy a.ppearancc. In case tw ph nocry · approach 

each other the tring or trand ~Lr apt to a · urn almo ·t or -ntir l J paral1 L 

dir ction. b ut el. ewh r c they . how n, ·on -tantl · var iuo· nnangement, frequently 

be oming wa1· ' or Rtr ng ly rinklcd, like th' rinkling of many ·blorite- and mi ·a-

:,;c hi t~ . Furthe rmo r , thi · :-tringy !-1 truetn r doe · not run uninterruptedly through 

the thi n · eti n, but i broken up into mor or l S ' parate ar as that have 

I nti ·ular Ol' twi. t d form . In g ncral the arnwo· ment of tb · gla y stra.nd 

CO lT spond with the cu tomru·y iiuidal trueture f o·las. y rhyolites and da ite , in 

that the tmnds lap or flow arotufd th ph nocrys ·, n,fter tb munn r of ·tring 

of mieroliti · in losurcs. 

Tb r •d portion of tbi.- dacite does not apJ ear to difi' r in thin s tion from the 

abov -de nib I black nr as, ' Xccpt that tt i · rowed with d irty look ing, browni: b, 

92 5- No. 8- 02-- ' 
114 PE'T'ROGR PHY OF. RATE:R J_, KE ATIONAL "PARK. 

a,nd app a r · 

Thi ' partial 

to tb wbol . 

powdery, ferri ic matt r. It COLPtitute the gr atcr part of be roek 

to indo e irregular, fray d out areas of tb dark r ·olor -d g la ' 

alt rnation f cl iff · r nt olo r d ar a lends a hrc c ia ted appeftranr 

Th cba nt teri. ti · . ·tru ·turc f tb i darite does n t d iff r ntially from 

. imilar tru tur ' as de cri bed b}~ ob rver I ewh r , b u t it reminds th writC'r 

for ibly of tb r d ob idian w·bich lddin;:::. has d s ·rib I. and of which h has 

g iYen a colored ep oduct <~ Tb pbcno ·rys · ol' thi.· da it arc not noticeably 

lift'er ent f rom tho ' in the da i · alread. · cl · ri b d. Tb y on i t of p lao·ioC'las 

and hyper t hene and f i ·olated, mi.nut r ddi h-brown hornbl nd . The ro k 

al o contain · -mall fragrn nts of a holocrystalline porphyriti byp r tb n -b arino· 

ba ·alt, and in on a o at I rut of a hya.lopiliti c andc it . Th frao·m nts a r 

with a few ox eption ' bardl.'' noticeable in th e brwd sp ecim n, as tb y arc sruall 

b u they a re v ry num r u , a c.teh of the two th in ection · p r pared from tbi 

ro k contain eight or nine s uch in lo. ures that mea ur from 2 r 3 millimet r · 

down to about 0.0:.. m!llirnet r in di.tm t r. 

The chemical analysi of tbi dacite ' ill b fou nd on pag 1±0. It will be 

noted that th amou nt of Ui a is "'or !3 p r c·cnt I · · than in th two otb r claci e · 

analyzed. nfo rtuuately th e pre once of th abov -m ntion d in losur e · of ba a lt 

vitiate to orne ex tent the rtnaly ' i . Th lo\\ er p r c ntag in ' il i a may a,..ily be 

explained by the pre encc of the e inclo ·ure , which may hav e h n I r ' nt in th 

portion s nt l'or aual ::;i to au ' \ ' Oil <>TCttt 1· cxtou t; Lbttn i indi ated by th t hi n 

e tion . 

L UD AP l:'LOW. 

This i. an exten iv fi w thrtt tart.· at loud 'ap and ext nd · for a,bout 3 mile 

in a north at rly dir cti n with a br adth of al out a ruil . Th e rock :pc irn n · 

collected from th i flow a nd in lu d cl in thi d scription a r No . 11 llU, 117 

11 ', 119, and 120. With the exception of ne di tinct!.'· lithoidal ·pe ·imcn (11 ), 

.~ ar mainly " ry g la y and al o largely . ph ruliti dacite , ·lo. e ly rc · mb ling 

th Llao Ro k ma · (a ,.;e n i n No . . 101, 10::,, a nd 10±). The g la ·sy portion f the 

ro k:; ba a light-gray color. Phcnocry:t of white g-la."y plao·io la " ar abun dant 

and pbe rio ry ' t::; of the fenomagn ian min rals ar c a r ·e. pherulites ar to be 

found i n No ·. llo, 117, and 120, b ut they ar con picuou ly Yi ible in th band ·pecim n 

only of the Ia ' t m ntioned number. Here they o cur from one-fourth to one-ha lf 

inch in diameter, n.nd have a whitish to lig ht-drab coloT. The larg r . ph ' rulit s 

are rn o r or k:s hollow and . how on th e ·rack d ·u rfaec a, fluted or rihbcd -tructure 

radiati ng- frorn the eentc r outwa rd. 

As this r o ·k doei.i n t differ " ry mate ri ally fro ru the :pberuliti · dacit : a lready 

de cribed, a. brief de ·c rir tion of th e mi c ro ·copic chamctcrs will uffi ce for present 

" c,- nth A1111 . Hcpt. U. S. G ol. urv y, 1 , p. 'l74. 
DACITES. 115 

purpo es. The glas y portion. in he spberuliti c varietie ·, a well a in the ntir ly 

,·itrophy ric g roundma of ro. 11 , contain characteri tic tr am of minut , tra igbt 

and colorle s augite mi rolite , like those in. No . 101 and 102 of the Llao Ro ·I ma. "· 

::\licroliti c feld par in the form of lath-lik plagio la ·e and r ectangular and nppa t·-

ntly untwinned feld par, occur in ,·arj ing amoun both in tb sam and in cliff rent thin ections. orne str ea.k may be almo t entir ely d void of ·uch f ld -p;H' 

microlite , while other may be crowded thickly with them, whil betw . n the· two 

xtrem ' th r appea11:> e\ ery conceivable intermediate tage. In two or tbr e thin 

sections, but more noticeably in o. 117, he untwinn d feld -par, or mor prop rly 

the microlitic feldspar, that doe not appear to have the albitic twinning, oc ur in 

very thin leaves that show ti·iking Carl bad twinnino·. Th two indi,·idual. that 

make up one of the ·e twins have each of th em imple quadrilateral form, and the 

leaves li e over ea h other joined by the cli nopina oid, whi hi · al ·o the plan parall l 

to which th little leave ar ext oded. Pr fes or Ro enbu ch refe r:' to ' ucb twinned 

microliti feldspar · a occurring in rhyolite pitch. tone and rhyolite ob. idian. o. 

116, whi cb how in th hand peeimen very trongly dev loped fl nidal stru t ure 

on i ts of alt rnating parallel :tr eak of Yitrophy ri , ph rulitic dacite and oi' a 

more lithoidal dacite fre from ·pheruliti inclu ·ion.'. Tb lithoid;tl ·tr ak · have the 

1 lagioclase lath very strono·ly developed and at time· bear a marked re.- mb lanc· 

to ·om of the Crater L ak ande itic rock . On th other hand, No. 11 ha · a br wn 

o·la g r undma inclo ino· numb rle omewhat granulat d augite micr [jte and 

i.- almo t fr from feld par roicrolit s of any de cription. lend r, -traight, and 

culT d opaque black trichit , a well a ' a v ry littl bla k ore in minute t grain ·, 

may al ·o b m ntioned a · occuning in ome of the e pecimen . 

Th ·pheru li · differ om what from tho e in o. 1 :1:, in that zon s of g-rowth ar e 

not ·o p lai nly d v lop d. Ther e i ' , how ,·er, often an inner, ·oal"e-grain d portion 

o~;c up:-in g th g r at r part of the ph rulite and an outer, den er, and usually deeper 

ta in d zoo . Th inner conr er part i mad up of radiating bred that how both 

po iti '' and n *'Lti,·e ex tinctions· u ually, howe,·er, po iti,1e. They a.l o have a 

t nd n y to fork at -ma ll ano'l and do not xtingui b ahmy.' parallel. 

Th pheno ry do n t pre ·ent any characteri tics peculia rly difl'~r nt fr m 

thos common to th e tber dacites with the po ·sible exception of hornbl nd , which 

i · rather mor abundant than I ewher . It ha · mo tly a g r ni ·h-brown olor, but 

a l"o 'CUL" r ddi ·h-brownin o.116. Jti · ah ·ent only in o.115. Iti of inter t 

to not in thi conn ction tLnt, although these rocks contain more hornblende than 

do th oth r dacite of Crater Lak ·till the actual amount i very mall indeed. As 

far as may ·be judged, a thin . ection from thi flow do s not ontain one-fiftieth or 

perhaps on -hundr dth part a muc.h hornbl nde a doe the dacite from La en 

P eak, to which r fer n e i::; made above, and with whi h these rater Lake rhyolites 
11 6 PETR GRAPHY OF CRATER LAKJ<; ' ATlO ' L P RK. 

ai·e closel.v alii d. I t shoul d f urth r be :-;tntcd thatoc asiona lnc. t · of old0 r :,; 'l'ction · 

ar e to b · en ·on' isting of plagiocia ' h.n er,tbcn . horn blend'· nug it . and mao·nctite, in wbkb horn blende i apt to be ,·ery abundant. Zirco n, which is o oft n 

r eported a. occurring in . ncb roc ks app a rs to be a r ar ace sso ry min ral in the 

Crater Lake rock · of all type . Tt wa · n ticed in ll . ino·] a,v. tn.l in Xo. L1 7. 

UN C'REEK FLo·w. 

This mas. ·include, all th da citic area to be . <'Co on hoth side ' of ' un 

're k, and str tching to tbe a t as far a · an<l 'r k. Th p eimens :stud ied 

o ._ 121, 1"'2. 1:2:-3 L±, u - 126, 127. Ko. 1±± como.· from a ·e r etion in 

dacite and will b d . cribcd Jat r. No. 123, wbi. h i · eli ti nctly d ifl'er ent from tho 

oth r ·, will be found c1' ·cribed on pao·e 1:39, under th head of . ·ecretion . No. 12 ' 

i: a dacit tuff. 

Thi is the only dacite rna to be · en on the ·outb id of l\1 unt i\Jazama. 

It differ from all tb abov -de ·crihed cla it in t hat a Mr. Dill r ha shown, 

it belong · to an ea.rli cr p ri od in the formation of the ,·ol ·ano and i · verl a in by 

andesite fl ows. Although tb inrli,·idual sr e imen.· above num rated Yary g r atly 

in their outward app ara nce they ar in gen ' ml ruu ·h mor thorourrhly cry -tallin 

than are the more r ecent dacit :s on th north m and ast rn ·ides of the lake. A 

g la y g-roundma · i not wan ting: i11 portions of tb .·c rock · but d ,·itrificfLtion, 

either co ntemporan ous with th cooling· of th rock or :·mhsC'q u nt th 0n•t.o, i. wtll 

d veloped. The rock". ther efo r , a.re 1 ttcr ·ui t d to n ::;tudy of th C' lithoidal 

type and will r e ·eiv mor ind i,·idual , tt, ntion than ha;; b n given to mo. t of the 

. pedmen tbu far. 

No. 121, taken from th e '" -t ide of un 'r ek 'an yon, i , a light-oTay . porou , 

and rough-fractu ring r ock. with incon.-pienous ph<' nocry t , a nd with num rou · 

rough caviti e · that are lin d with minut "-bite glass · c1·ystal . om of the 

cry tals, . raped from the cav ity with a knife, p ro,·cd t be trid}:mit , tog tbe r with 

ome feld. par imilar to that d · rib d later a. visible in th thin :ection lining the 

ad ties. 

nder the micro-cope th e ground rn a ,, appP.n.rs to b in mo t place , bolocry talline, or at lea: t one in wbi h a glu:;s ba:c play.- a" ry . ubordinate role. H e r and 

ther e, however , the thin c ti on a .' '-' UOl . a b rownish ca ·t, incl i ·ativ f abunda nt 

g la s. The colorlc.-. partie! :;, which appear to mak up the hulk of tho g round -

mas , ar neithe r elongated nor sqmu·i b in crosf' section . hut ba,·e ill-d fin ed, 

roundi. h, allotriomorphic form . Throughout thi , g ranular ma'-' , ar c cattered minute 

opaq ue dust-like or p:!rticles, and al. ·o many minute yoll owi h to colorl s du t-laden 

augite microlite . In g ula r longi b cavitie · aboun cl . the larger of whi ch are 

empt ; tb mallcr one are often filled with tridymite. Between this tridymit 
DA I'T'F.S. 117 

and th wall of th cavity i ' a narrow fringe of olorl 's "Tains. the am to all 

appearances a those that fo rm a large par of tho gr un ma~. . \\'b re,- r the e 

rolorl .. ·gr ains ·omc into contact ·with th Ca nada bal am th y arc sc n to baYc a.n 

index of r efraction lower, but only Y-ry li o·htly lower than that of he bal am, o 

that th dg of the grai n ca n hardly bl' di::.tingu if' hed. Th ey ea n not tb refor , b 

qua rtz. Th · ar structurale · and without twinning- band . Tn polarized lig ht tb 

polari zation colore arc much higher than in tb adjacent tridymitc. om of the 

larg t of tb grai n · (0.0:2 to 0.03 milliuwter) g ive biaxial image · in convoro·ent 

polariz d light. In ~0 ea ·o a di. tin ct d ea ,·agc \Ya noti ·eel with an extinction angl 

of 7t0 to the trace of the cl ange plane. 'om·ergcnt polariz d light o·ave a po itivo 

large-ano-1 d hi. cctrix in th c nter of the field, with the plan of th opti cal axe 

incli n d 7!0 to th tra e of th cl a,·age. The e prop rtie.- would ·crtltinly indicate 

ortho Ia 111 whic·b ca the g ra in ju mentioned is ·ut nea rly parallel to tb 

clinopinacoid. The ·o fringing OTain ' a rc fre from solid in ·l . ur , , but th y ar pear 

to contain g·a por ·. 

That. in pit of th above-d scribed properti ' th .- grain ' arc 

probahly not orthocla c, llJfty appear fr rn tho followin · two con ·iderati ns: l<'ir t, 

the index of r fra tion i' too high fo r ortboclas , althouo·h, like ortho la ·c it is 

lowe r than that of the Canada baLam, who' e ind x f r fraction i · taken to 1 

L. 5-:1:0 . OrthoL" Ia e whoso index of r fraction i ab ut 0.025 1 ss than that of 

bab;am, should pr en a harply d fin ed dg at co nta t with tho bal. am. con l, 

many or \' n liiO::>t of th . gTain · ba,· an unclulous xtinction. Thi ' cond 

on id ration won II uo·o· ' t th pre ene of anorthocla · , which would al ·o be 

OLT horat d IJy the pr ponderanc<' of Na20 o\·er K2 0 a ' hown in the chemi cal 

a naly of the Crater L ak da itc ·. On tb otb r han d, th ind x of r fraction 

of anorthocla · n · g iv n by Pr f :;or Ro.-enbusch " i.' only 1. 5:r, which 1 · but 

.0 2 hi ·h r tha n that of ortb . ·lase. LTnle. th erefor , .anorthoclas hould I rove 

to p c · a high er index of refracti n than that h r gi,·cn i would seem that 

thi ' f ld ·par mu ·t l pla din th alb ite-oligo l,se .- ri · in pit of the fact that 

no twinnin Q" i' to b s n. 

It i \norc than likely that q na rtz f rm a larg par of th cry:ot.'Llliue 

gT undnms ·, but owing to the ·mall izc of tb particle · this ould not be 

demonstrated. 

Th tridymit of thi rock do e the cu tornary . hiugled a pect. 

lt do probably c ur 1n m r r o erlapping calc.·, but the dge. are 

irregular Md th e o,- dapping not v -ry ·on pi cuou . The occmT uce, howevei·, 

xn tly I i k , that of th tridy rnit i 11 the lithoidal rhyolite from Ob, idian Cliff 

ati n,tl Park as xamined by the writer in ction ' from that 
11 PETROGRAPHY OF ORA'l'ER LAKF. A'l'IO AL l' RK. 

rock In the poss . -ion of th e min ralogiea l laboratory f Harvard Tniv r ·it . 

In de cribing th e occulT n e of tridymit in th e rh,rolit . from Ob idian '!iff 

ldding .. · ay : b ' Th pa ·x· ·x· ·X· ar in mo.'t in t..'inc · oc npi d by tridymit 

in c mparati\· ly hug crystals, oftC'n twinn d and carryino· nun rous ga · ·av iti ' . ' 

The tridymit in thi nn r ek dacit may be re ogniz d by the foll owing 

properti ·. It oc ·ur in minute ery tals or grain,; that measur 0.05 to 0.15 millimeter, u ·ually filling th e avitie . Twinn ino· i.· ,. ry common. om time· th 

twin. r emble those of orthocla:'e in the form .of Carl bad twin. th twinn ed 

halve. having widely cliff' ring extinction a.ngl ; in other ca · :· th r ' app ar to 

be twinning planes in ruore than one dire tion. Undulou · xtinction i " r ' 

common, but wher e the bYinning is w 11 marked this i not mu h in vid nee. 

Exactly similar undulous extinction was al o noted in th e . C"tion. from 01 idian 

Cl iff !thove r efen d to. Interf rene color arc very low, om tim : being ;cdmost 

rrisib ~. The refra ction i much low r than that of the adja nt hal -am. Thi · g r at 

cliff r nee in r fra tive powers is -trongly brouo·ht out hy th extreme rougbn c " 

of the tridymit , a well a by the ·harpne of the edg · · a compar d >rith the 

oTeat moothnes. of the urface of th feld par grain fringing th caviti s. 

Except for th pre nee of g·a caviti , th tridymite i. fre from inclo ur . 

\mong the phenocry t · of tbi rock are fairh abundant pla io la ~ 

·paringly developed hypersthene, and only an or a ional minute au o·it 

Hornbl end was not to be een. 

, rath r 

ry. tal. 

pe imcn 1. o. 122, oUc ted low r d wn on th e west ·ide of 'un 'r k Can on 

n t far from No. 121, i: a slightly I orou: light-gray ro I of lithoidal hara ter 

mix d to a certain xtent locally '" itb dark gra}'i ·h-gre n gla y p rtions. Both 

th lithoidal nncl g la · portion are c rowd d with mall . ph rulite , 1 to 3 millim t rs 

in diamet r. ~1o t of th e' e pherulitc · ar olid xt rnally , and of a dark-oTay color 

withi n on th e f r . b ly fractured fac . ome ar hollow and . how a ·light tendency 

toward tb f rmation of conccotri ·hell or lithophy ro . 

nd cr th e micro ·cop th greater part of tb rock i · een to be compo d f 

. ph rulite.- of di:tin tly recognizable fiber an.d . hr d. that radiat in branching, 

f athery form. from r.ommon ·euter . These apparently f ld pathi · fiber hal' 

both po ·itivc and n gative, but mo re commonly po iti e, ext nsion, and xtingui ·b 

both parnll el and obliqu . Whether they a.r a tually intcrgrown with quartz can 

not po:iti'' y be a rted. The outer portion of th ph rnlite u ually contain: 

d ep browni ·b-red scales, presumable of hematite, that polarize ligb . trongly. 

They racliat from th e center and bran hat 1 wangle. . To the e browni ·h-red ale 

i du the r eddi ·b color of th e outer portion of the pberulit . a seen in the band 

. p cim n. The two thin sections prepar d from thi rock were both cut from th 
DA ITES. 119 

li thoidal part of th e ha.nd pecim n, so that they do not bow any gla' under th 

micro cope. The g roundma · ou ido of the pberulite._ 1,; em · to b h oc tallin , 

but xtremely fin e g rained. Th individual grain arc to fin to b determin d but 

they app ar t baY no particular elongation . Through thi. minutely granulated 

g roundma s, a. well a-· through tb ph ru1ite ·. run : tream.· of 1 nd r, rod-like 

auo·ite microlit . and of minute 1 ut not ,-ery abundant bla k or particle , to whi h 

·bould b adele I an occa ·ional lath-. hapcd plao·io ·la microlite. Phenocry · occur 

the ·am as in o. 121. 

Jo. 124 i an a.gg reo·a.te of v ry light-gray, porou.·, a.nd di. tinctly r talline, a 

w ll ar of ,-ery dark-gray den e part·. In the thin ection tb oTanular part ba, 

mo tly disappe:n d in th grinding, but from what i left th y ·eem to b - ompo ed 

of an aggregate of colorle" , allotriomorpb ic grain , I robably of feldspar and qua rtz, 

with occa ional tridymite sca le . Tb den· , da rker-color cl part · probably ontain 

a glas ba e completely ob cured by the de,·itri(ication product ·, whi b on i t of 

auo·i microlite granulat d with adhering and in lo ·cd paque ore I arti lc and of 

extr mely minute, olorle·: allotriomorph ic shred. and grain. . As in Ko. 12"', tbi 

rock al o conta.in a very f w lath- haped plagi ela!:ie microlite ·. 

The phenocrys con i t of the cu tomary plagio la e with al o a little hyper -

thene and two or th r fragm nts of brown bornhlendo with bla ·k re orption rim ·. 

No. 125, from n ar the bead of th IV st Fork of and r ck, is om what 

' imilar to tho la t-de rib d pe im n. but the oToundma ,; i mu b oar: r g rain d. 

Tb ·hr del d app a ranc f th olorl ingr cl ient i ,·ery mark d. but tb ir xa t 

tnineralon·ical nn,ture can not be mad out. The· hr d. do not r a h dimen ion 

gr at r than 0.0. millim t r, and ar too mall to cl arly eli clo twinnin o· ,;triation, 

altbouo·b th e la.rg r ones lea,- th impr sion that poly yntbetic twinning i pre nt. 

In whit light tb granulat c1 n.ugite microlite . how up v ry clearly and abundantly, 

ven with moderate mag nifying pow rs. P lagioela e and byper ·th n ar - the onl.r 

ph n cry · noted. Thi" ro 1: b ar · a lo ·e re erublance to No. 113 from tb leetwood Cov ma . 

' o. 126, which \Va collected do e to o. 125, ba - a Y ry d n 'o tru tur a.nd 

clark-gra r olor. It l ok · de id -dly like an ande it . In thin cction it doe not 

RPI en.r a ltog tb r ven grain d, but clisclo · coars r-g-rained patche . It is, hov.r-

,, r a · a rule, very fin e g rain d, or ~tt I at, app ar ' O in white lig ht, in which it 

:1ppear t be compos d of a uniform wbito ·ub·tanc very thickly prink! c1 Yl'ith 

opaque black du ·t pnrticle . 1\ ben t rono·ly magnifi d the e du t particle ap1 ear 

a. black or grain ·, and al ·o a tran parent or tran ·lucent globuliti matter. The 

granulat c1 augit microlit s ·o commo n in other pecimen from this lava rna are 

almo t ab. nt. In polari zed light the . continuous white ub tan e appears to .be 

made of very irregular, interw aving allotriomorphic pat hes that remind one forci-
120 PETROGRAPHY OF RATER LAKE ATIO AL P RK. 

bly of the allotriomorphi feldspar patch · of ma,ny of the holocry t.'tllin and it 

of tbi ' r gion. They are t b di ting ui heel from ·ucb b tho ttb · n ·e of in lo d 

plagio ·la e lath . Plagioclase and hyp r tb nc occur among th ph nocry::;t , a. 

u ual. On auo·it cr" tal was notic d · also a oTain of nutQ· netite unound d with a 0 ·' ·~ 

rim of leu oxen . 

No. 127, from near and re k, f urnii<h s tt beautiful illu tration of fluida l 

::;tru ctur , both in tb hand ·p cimen and in the thin ' ctior . ln th form r it 

appear in very thin alternatino· parall I band:::; of lig ht r ddi ·b-gray and of darkgray and v ry ompact mat rial . Phenocry t · arc ru ~tll , l>ut quite a.bundant, and 

are ma.de more cou I icuou.· by the evid nt flowino· of the e thin band around them. 

Jn thin section th e fluidal ·tructure i · beautifully br ught out, both by th 

alternation of coar er, ,·vbit band with fin r-gT tined and 1rowni h- olored band 

and by the pre ~ nee, e pecially in th finer-grained ·portion f ' tr ak · of bla k 

du -t. \iVben examined with strong pow r. thi appar nt ore dust i · en to be 

·ompos d in part of inclu ions of ail" in part al o of r ally opaque pa.rticl that 

are u ually to be e n inclo d in augit microlit s. .Th whit band. apr en,r to 

be entirely ry talline. They ontain omparati,· ly littl mi roliti mat rial, e ith r 

in the hap of augite r or , p<trticle . In polarized li D'ht the rolorles.· material 

br eak" up into ver) di tinct, long i h . hr d, quite ·imilar to tho e d ril d abo~·c 

in oth r p cimen. from thi. dacite rna . Th y a.r , p rhap ·, ·omewhat mor 

di tinct here than I ·ewhere. Oc a ·ionally .·om of tb l~u·o· r and bett r-d fin d 

. bred. (0.1 millim t r ,. more in longtlt) ~:~ how di tind. l\\ inniug lm11d LuL lbi. · 

lti exc ptional. ~lo e frcqu ntly the x in ·tion 1 • mor or le. ·' unoulou and 

som tim :-; markedl.Y o. In o·en ral it i · nearly pamlle l to tb ex ten ion and i 

alway. n o·ath· . 

The sbred-lik :::;trip bow a trong tend ncy toward grouping th m. lve 

around ·ommon nt r . Three, four or tiv or mor of tb · may be see n 

diverging from a, common point, acb of them narrowin · d wn wedg -lil<e at the 

cent r. in the case of the more iE:olat d bred · the ar al o negati They 

tbu produ what Ro nbu h calls " p en do phemlite " with n gati ,. ro. eL. 

ln tb mid t of the ' p udo ·pherulite ' may al o b en the ordinarr ' ·true 

·pherulite · ' of Rosenbu ch, a.l o with negative ro. se . The.·e latter d not appear 

to be ·ompo d of any r ecognizable mineral :pecie . They ·bow th e cu toma.ry 

bla ·k ·ro · with arm pa,rall 1 to tb prin ipal plan :::; of the ni ol pri. m:::; and r main 

tationary upon r evolving the stage. They do not ·uece d in d ,·eloping 

externally ·pherical form , a their growth app ars to be interfer d with by contact 

with th <"Oar er-gmined portions f the groundma~ . Every pos ible gradation 

app ar. to pre nt· i elf between the · ·o-call d .. true ·pberulit . " and th radial 

g roup of cry tal particles that appear to be undoubtedly feld pathic. 
DA I'.rE . 121 

Th fin r-gTained band. with browni h olor arc ompo · d, appnr ntly, of gla 

with in lo ed du t partie! . . But upon ~ r in ect on h apparent g in " "e m to 

be compo ed of ill- l fin ed parti lc that. wing to their parallel nrrfw o· m nt , r 

faintly polarize lig ht, o that th who! band xtino·ui he " panlll l, with nogati11 

xt n ion.. Thi:; i undoubtedly the 'lt b tan c o fr qn ntly r cfcrr d to in 

d cribing ucb rock a microf 1 ite. On a h ::side of th .·c unit rmly polarizino· 

band of miorufeL ite o ur 

ind ividual pheruliti part 

"true ·phcrulitc . . 

a very narrow. co ntinuou ' . ph ruli ti . treak tlw 

of which flr quite ·imilar to th ab v -m ntion ed 

The pbeoocr y t in thi rock are . imilai' to tho - in th r . t of the dacite , 

oamel:r plaD" iocla e and hyp r ·t hen e. H orn bl nd ould not be e o. 

D ACITE TUFF. 

The depo it of fin Yolcanic material that i to b een fillino· th bottom of tbc 

afld Creek anyon i. r pre. oted by No. 12 . Thi. i · a; loo ·c friabl dark-gray 

tuff. Examined with a pock t magnifying gla it appear to be compo. ed mainly 

of du t- over ed wh ite g rain with an n.dmixture of sonw bla k cry tal . Th whit 

g rain · turn out to be plagiocla and the black one · hypersthene and hornb l nd , all 

of them exa t ly . imilar to the pb nocry t f th abo1· -d .' rib d da it . Tn 

addition to th . ;-~· ta · and g rain.· thor occur Hmall (3 to • mil lim t r) ano·ular 

fragment of ·ompact dacite, or pcrbap · n.L·o of a,nd ito. 

Th plagiocla:;c d . not ha1·c tb fo rm ·o ·w ll pre crv d a do the other 

mineral . Th hy persth nc cry. t.<tl bow the cu tomary unit pri m and two 

pinacoid , while tbe hornbl nd ha.· on l. the prism I arly ·hown. Tbe hornblende 

~ th optical p roperti <' imilar to tho e gi11 n for tbe phenocryst" in th e dacit . 

That thi tuff i u ndou btcdly dacitic i. demon trat d by the pre nee of tbc e 

abundant hornul nd •ry tal. which a,ro a lmo. t entirely confined to tb d::tcitc of 

'rat r Lake. 

n cnti rely analoo·ou. daci tuff i · to b ecn in th bottom of th A nna Pek 

Canyon (N . 129). · Thi tnff al. ·o c~ntain ' hornbl ode in great abundan , 

DACITE DIKES. 

mong the dil-e that cut the and iti rockH of tho cr ater wall are two underneath Lla Ro k that ri f rom tho water' · edge and con i ·t of dacite. The mo r 

we terly of tbc · two dike·, imm diately under the ummit of Llao Rock i:s r preen ted by two p cimen , Nos. 130 and 131. Tbe fir ·t of the i a very lig ht g ray, 

porou , lithoidal dacite a nd come· from the central part of th e dike. Tb econd i ' 

a grayi b-Llack g la · and wa ol lcct d at tb margin of th dik . The two tog tber 

may be taken as the equivalen · of No ·. 103 and 102, r espe tively, which r pre C' nt 
122 PETROGRAPHY OF CRATER LAKE ATION L PARK. 

th e lithoidal and the dtrophy ric dacite.~ of th Llao I ock ma nd r the m1cro· 

cop the re emblance i · till mor strikino·. No . 130 and 1 1 both co ntain th am 

ph nocry. t alr ady de cribed in th equ i,•alent ro k. · abo,· l1J{'J1tioned. Ther a rc 

comparati,·ely abundant plagiocla.- with Jarg cxtin tion an o·lc and zona l tructur , 

cant.r hyp th e and augite, a.nd occa ional g r ni. h-br own b rnbl end , togeth r 

witb acce · ·ory mag n t it and apatite. The lithoida l ro k from th main part of tbe 

dike doe not cliff r sufficiently from the lithoidal dacite f the mmmit to ju tify a. 

·pecial de c ription . The g la y margin how ' r , pr ·ent min or f ature. · that 

eli tino·ui h it from .No. 10..... F luidal tru tur i v ry p d cctly d ,-el peel an 1 i 

accentuat d 1 otb h) the ,·traight au ·.ito micro]jte·· and hy trenm · f r ound i:h. nearly 

color] s obu lite~ . Th color of th e gla tream · a lt rnate ' between wbiti ·b and 

brownitih. H r and th er e a little clea r brown gla · . fr c from microlit ;· and 

globu lite , i ' to he een in clo e proximity to a ph nocr)'.'t. Tb thin . ction of tbi · 

·pecimen al ·o · ontain. se,- ral mall fragm nt · of n. fin e-gmined holoc r tal l in , 

porpb riti c ba t, in th g roundma of which are to b n lender pr" m f 

augite and hy per th ne, a l o grain of mag netite and plagio la "e lath . 

Thi · d ike i undoubt dly one of the fe d r of the Llao Rock dacite. 

The more a terly of the t~ o dacite dik .- i r eJ r s nted by only one -pecimen, 

o. 132. It i a light-g ray , coars , r ough-fractu ring ro k. nd r tb mi cro· ·ope 

it pr -ent: featur · . omewhat . ugo·e ti,· of the Grou Hill dacit , but th ·imi larity 

i · not mark d no ug h to ju ·tify th e co n Lu. ion that thi ~ dike i.- a fe dcr for thi 

dacite mas . The ro k i: not altog ther fro h. lt ontain ·· in additi on to th us ual 

phenocry. , a Y r y li ttle reddi ·h-brown horn blend in mall ry. tals and !rag men 

with black hord r . Th oTounclrua · contain. th usual hort r ctang-uhir f Jd par 

and a good deal of f eld pathic ma tter that ba · no wcll-d etin d hape. Browni ·h 

and r ddi h f niti rna ter, tog tb r with ·om hlack mag n tite, r nder the th in 

ction cloud d and dirty looking. Abundant o-roup · of tridymite ar to b een 

:filling what appear to b cavitie . 

Thi · dike contain an ioclu ion Ko. 133, tb nature of whi ·h i · not clear. It 

bu. a ·lig htly greeni h- oTay color i · di tin ctly l:)ut fin ely granul a r, and i decidedly 

p orou. . I n thin e tion it i ·· e n to be compo.-ed ·seotially oi plagiocla: l~tt s 

a nd of hyp r th en and augite in mo ·tly long, 1 ndcr pri m . Grain · of bla ·k 

magn tite, n · well a r ddi h and brown.i h ferritic staining matter, arc abundant. 

Por1 by rit ic rystal are ntirely ab nt. Th ·bape a nd a rrangement of the main 

ino-r cl ient , b ut more e pecially of the p lagiocla.- lath , ar lo elv ana logou. to 

tho e of in ter titia L ba alts, although it doe not agree with any of th e ba alt. from 

Crater Lake. But th er e a re other r e pects in which this inclu ·ion eli tinguishes 

it lf from the ba. alts of this r egion. It co ntains con iderablc reddish-brown 

hornblende, and in some of the inter tice: between the plagiocla e laths are colorless 
DA T'l'E. 123 

aggreuate that appear to b tridymite . imilar to that in th dike ro k. It i · 

proba bl that there i . . or wa, , on 'id rabl uta ' in the form of a me ·o ·ta i ·. But 

if ::;o it is largely devitrifi d and color d a dulli ·h gT n. The th in section i too 

thi ck to al low a sati f ft ·tory examination but th e wri r i inclin<'d t pia this 

:p cimen among th e :e r etion. of dacit . It alls to mind a not , ry di imi lar 

pe ·imen described among th dacit o. 123, from un re k. ( ' 

page ).39.) 

DACITIC EJ E CTAM E N T A. 

The large amount of volcani c ejectam nk'l. that over th uda · of the rater r im 

in 'ariou.· place ·. e, p cially nn th e north rn and west rn :-ide. , and that form , xt nsiv d posits ov r th e u- call d Pumi De rt, app ar · to be almo t ntir ly da ·itic 

in character. 

orne dark-co lored sa.nd , o. 13-t, colle t d n the Pumic D . ert is <'Omi o ed of 

th e lig ht- and c1'lrk-colored mineral. c urring a" ph nocry t in the dacite ·, as w 11 

a of brown gla :; . The are plagioclas , by p r·-th n , bornblend , augite and magnetite. Th ·ize of tb ,e ry tal varie f rom ab ut :.~ millim ter " downward . P lag·ioclase form' th mo t abundant of the . and partide-, with f rm that ar u uall.r 

roun di.' h but that al o may be \Yell r. stalliz d. I-Iyp r then , on the other band, i. 

ve ry common in th e charact ri ti pri mati forms witb th e unit pri m nnd wo I inac id ·. When fin ly pulverized and xamin d nnd r th mi ro or e it i , c n that 

hotb byp r then e and dark OT ni. h-brown born blend are ,-ery abundant and I re nt 

in about q ual am unt . .Augit an l mao·n tite arc rather ·care . Th e latter can 

r a lily b par at d from the and by a magnet. Thi and exa tly r emble the 

oar' cr part · of th e tuff found in th bottom of ' and 'r e k Canyon cve ra i mil : 

b low th crater rim (12 ) and in nna 'r k Canyon (129). The accumu lation of 

th py rox ne, and of hornbl nde to a much gr&'l.ter extent than in .th dacite :i. very 

noti a bl in both tho tuft and ·and d po i . 

odim nt brou ubt up from tlw bott m of th lak on th e we-t id e. No. 1357 

app ar::; to h ompo, d of , omewha imilnr mftterial n. the aboYo. hut as it i ,-ery 

fin - th laro· . t urains b ing not much o,· r 0.1 millinl' ter- and entirely compo ·ed 

of angular fragments l.h p r ccntag <' of tho dark-color d pb n cry t , or r:ttb r of 

fnwmc nts of ph nocry ·ts i. comparatiYely mall. This i pa1ti ularly tru of hori?-

bl endc which i. ,·cry car e. On th e oth r hand , g la · f ragm nt: are v ry abundant. 

Tb nature of this · dim nt i · not w II characterized a · to mak certain wh tber or 

not nnd itic mat0rial i largely mix d with th dacitic a-b. 

Th coar or ej ctam nta wbicb have b en coli cted and ' ubmitted to tb writer 

for inv tigation may b divid c1 into three cla e , viz, pumiee d~•rk -color d cretions, light-color d granophyric ·e ·r'tiou . 
124 PETROGRAPHY OF RATF.R LAKR A'l'IO AL PARK. 

P MICE. 

No. 102, from the ummi of Llao Ro k. is an almo t pur pLtmi f a pinki ·bwhite olor and extremely light ancl porou ·. \Vith a mn.o·nifying o·]a .· OLH' can drte ·L 

a very f w g la y plao·iocla cry tal -, and a,lso till f c\\' 'I' clark-e lor d pyroxe ne or 

horn blend ph nocr,r , imilar to th phenocry ts in tb Llao. Rock dn. it . nder 

the mi ro op thi rock pres nts th cu ·tomn.ry porou pumic ous stru tur w-ith 

long drawn out ga.· pore · but the gla cliff r:; from tb · itro1 b.) ri po rtion · of th 

Llao Rock f!OYI', in tbat the ver characte ristic r l-likc augit micr olitc. ar almo t 

nti rely mi in g . \. fr w phenocry. of pln.gio Ia in cry tal and cr.v ·tal f ragm n 

are to b e n. also an occa. io nal h ·per.-tben and wo or tbr minut brown homb le nd ·ry tals. One of the pln.gioclas' ry tc'tl wa c n to ontain num rou 

in ·lo:ur · of apatit and a l o vera! clark-bro·wn g la , in Ju ion , in n of wh ich 

wa · an air bul bl . No. 137 i a fragrn nt of pumice oll -ct d from the sn,me p lac , 

and cliff rs on ly in being mor discolored. It ntain: ·imilar phenocry. t. , an l al o 

b row ni ·h gla · inclo ur . with ga bubble· in th plao·io Ia . Thi pumi . evid ntly 

i of the sam chara.ct r a · the dacit of Llao Rock. 

'o. 13 i · a ·p cimen coll ted from a. la rge fragm nt in the Pumice D rt, 

th e north of Cr at r Lake. 1t ba ' a b rowni h-yellow color and look ns thouo·h it 

f'Ontai ned mor o r l : layey matter. lt aJ-o ha · a fragm ntal l'tpp m·anc a · tbouo·b 

it we r <t br e ciatrd rock compo •cd mainly £ pumic . It al o con tains a frw mall 

frngm n th,tt app •a1· to be andc itr . Plag ioclas grains nrc very abundant in tb 

band ;;p cim o, but th thin ·ection contain · hardly any. a. tb y haY pr bably di, -

appear d in .the o-rinding . A v ry few minut hyper th nC' nnd augi cry tal and 

one small fragment of r eddi. h-brown hornblende wer e noted . 

In adflition to tbi. ordinary pumic arc al. o frao-m nt of a di tinct l pumiceo u8 

rock of light color in which ar r eadily n num rous bla k cr y tal mo. tlj- bornbl nde. Th hornblende cry tal vary in siz from on -fourth of an inch dow nward. Probably nr-eightb of an inch in I ngth i. a fair a,-erage iz . One of 

th ese fragm -nts wa · collected on the north a ·t rim of 'rater Lake east of Round 

Top and another (146) from the ummit f Red Cone whil two other. wer col.:--

1 cted by th e writ r on the rater rim ju t outh of Llao Ro k (2011, a u.nd 2013. 2 

of tb privat· col le ·tion of H. B. Pattoc). The fenoma,.;1.1 ian mineral · ' hicb ar 

,·ery conspicnou.· in the baud . p cimen are ·till more apparent in the thin · ction, 

as, ind eel, ar al.·o the colorle . plao·iocla e phenocry t . . Tb groundma. of tb 'e 

·pecimen do · not a.pp ar to cliff I' materially from that of the mor typical pumice. 

It i a nearly pur o·la ·: . fu ll of longat d a ir cavitie and more or le s tained with 

yellowi b to browni ·h ferriti matter. Only a f w augite microlite and but little 

magnetite du t i to b seen. On the other band all the mineral that have been 
D.A TTF. . ] 25 

m nti ~ as occunincr among tb phenoe ry:-;ts in th, ' rat r Lakc dacite " ftnd 11ntt 

ar th r ' paringly dc\"(' loped arc- unu ·nally num r u · in th .· , pecim n . Th 

minera ls he re included arc plagioc ht ' C', h rnbl nd, h.rp r ·tb 11 r . and augit All 

but the homblcnde ar pea r to ocem· in nbout tb c snn1e : ize. ns in the dacit s. J n the 

en. c of plagiocla e th rc is de1eloped a 1·ery :trong tendency to in clo. e eompamtiv ly 

la rge and irregularly lob d a,nd mor o r I s;; onn ct d inclu ion of ,. ry d q brown 

crl a :;. The. c inclusion: a rc not arranged aro11.11 l th mrtrgin in a wcll-ddincd z n . 

11.' i · i'O f requently th ca,;e with th phwi ocla phrno '~' 1 ·ts of thr and itc but 

tb y nr more c1· n l,r di ·tri hu ted tb1· ughout the cr.r:;ta l a,nd p rod u c a . tructu r that 

may fair ly be hamcterized as :pongiform. These :-;potwiform p lag io lase · a r b · no 

mean as ommo n or chara teri. tic a · th .1· arc in the dark- ·olorcd s . 'I'Ction , ho 

de cripti u: folio"·; neith r do :tll or v 11 mo t of th plagiorla:;c phcnoc r ''k have 

the c in lusion ' , but their appeant n · her i: important rt · fo rmin o· :1 link betw n 

tb dacite and th inclusion in the am Fracturing of the feldspar i ,·er:r 

noticeabl . 

Hyp rsth n and aug ite occur in the ·am fo ru1 :; ~tnd with th same gen ral 

prop rt ic ' a in the dacit . . Perha1 s a ·trong r tcnden .v i to h noted t ward 

rounclirig- of the edo·e , partic·ularly at th nds. Likcwi. e indu -ion. f glas · a n I 

' >SP cinlly of br wn gla.·s nrr more ah undnnt. Th most int ' I'C ·t ing mineral is hornhl nde, who e abundan ce i.· increa: d r Jativ •ly much more t.h:ln is h ut~ with tb 

other ph nocrysts. It aJ. o ·cur in very mu b l<trge r ·rysta l: than nr to b . c n 

in the dacite . Exc pt for ahut1clanc and iz . howcv r. th :-;e hornbl nd cry. ta l: 

do not 1r ~ nt nny mark cl p cu liariti ' . The.'- show a , trong- tend n y to de1· lop 

the unit pri ·m and th - I inopi na o id , but thry an' u ' uall.v brok n into frao·ments I i kc 

Tn col r tbe.ntr' similar to tiP hornbl ndc ·of thc- dacite. . Gr ni h brown pr domi1mt s b u the more reddi h color;:; are al ·o to be , en, notably in 

o. 1. 9. )lag nctit occur: rath e r : pari no·ly in tb :e r o ·ks ut the form of di:tinct 

grain in ·lo · d in the pheno ·rrts a , w ll a:-; :catte r d through th o·las · groundma . 

DARK-COLORED SECRETIO. S. 

Th :p are fou nd a · eJ cted frag ment.-; tog th r wi th pnmlCe. They occur a•' 

cxtrcm ly dark. :dmoHt black. Yery por u · and roug h f cling bomb~, and contain a 

g reat abnndan ·c of bla.ck I enc~ and ! lack. horn blend ~ w •U a of the g la · ·y 

plao·iocla ·c. They ha1·c ll wi d cl i::;tribution, as may b r-;een from the fo llowing li.·t : 

1\o, L+l eOJc1C f n m th .Pumi c De.:c rt to the north of rat!? r La k ; No. lL from 

n M the . ummit of Dutton lift' to t he. outh o f the lake; No. l±' from th ·umm it of 

Llao Rock ; To. L+5 is a fragm nt front a co ng lom rat that ov rlie-· a mall ·beet f 

dacite just above Grotto Cove; a nd :Wll, b (p r·imtc collect ion of the ' ritc r) form -· 

part of a la rg<' hont b attach cl t th e pum ico. ·p eimen. 20 Ll. a, aho1· cl . rib cl. T h i, 
126 PF.TROGR.APHY OF CRATER LAKE .A TI N.AL P RK. 

Ia, twa ·oil cted ju t · uth of Llao Rock. Tn pit of th dark olor of tb ' rock th 

ferromagn ian rnin rals are quite on picuou . Thi i pa1ti ularl · tru of o. 

2011. b, wher e hornbl ende i more abundant than in th other pecim ns and i r ecog·-

nized by mean of th brilliantly fht · hi no· l a1·ag .·. Thi min ral o CUl" h e re in 

cry tal that ruea ·ur up to 10 millim t rs in length nnd 2 to 3 milliw t r ' in width. 

Under the micro · op in thin s ction th · ro k ar e n to ont.'l in a,. r darkbrown , o·la sy groundma s that inclo ·e but f '"aug ite mi ·r lit . but is cr ' del with 

air cavitie . In color and g nend app aranc th groundma ·:,;closely r mbl . th 

gla. in clu ion to be · en on tho plagiocla c Cl') tals of the hornbl ndi pum1 · 

abo11e mentioned. It forms from one-third to on -half of th rock ma ' ·, the r t 

b ing compo eel of pheno ry. t and fragm nts f 1 hcnocr)?t' . 

The plagio la' e r y k'Ll belong to the type de crib d und r th clacit a · 

ccurring in rather lurge, 1lump cry tal. , with num rou · ·ry. k<t l fa c.· . R ctang -

ular ectio n are rare, ·o rare, in fact that th ey arc probably only chan c ction of cr y tal of the typ ju t mentioned. The plagi h . ·e ·r:v tal show <l :trong 

t nclency to a.· umc idiomorpbi form. ex ept in :o far a · they occur in r< battered 

fragmen , but they arc g n rall roweled w ith irregul ar brown glass in lu. ion 

o a to a sum a thoroughly . potwe-Hke appearan .• imilar to but mu h nt or 

pronounced than the pongifonn crystal' in ·omc of the pumi r frao·ment.-. Th · 

ramifying g la 's in lu: ion: ar not ·on fin d to tbC' int rior of the cry 'tal, but 

come to th .-urfa. e and often appear a:,; cmbay mcn · filled with l rown g la. s 

xactly like and •ontinuino· th e g la s of tb g-round rna s. F ig ·. ,., l, B, and (' f 

Pl. XVII a re r production -· of ·ome of tbe · spongiform plag iocla ·e ny -tals and 

g iv a fair idea f the ir app aran('e. The plao·io ·Ia. e i probally all ba ·ic and , 

in some ca e , demon. trably :o. For in ' ta nc , in o. l43 a boneycoml eel I lng io ·la e 

cr ·:;tal , with zonal tructur aml cut ymm trically to the plan of twinnin o· o·a \'C 

an xtinction angle of 47° in th center and 37° at tb maro·in. Tbi indi <Lte · 

an xtremely ba i anortbit . mor ba ic in fact, than th mo ·t ba i of th 

plagioclase who e extinction fLlwle · wer e mea ·ured in itber the ande. ite. or 

ba alts of rate r Lake. ot all of the plagio ·Ia · ·ry tab bow noly ·ynth ti · 

twinning, but mo.-t of th 111 :'ihow·eitber thi · twinning or a zonal structure, and 

no r a on wa apparent for con idering any of them to be ortbo la e. They 

co ntain in lusionR of ore ·, apa,tite, and hyper tb ne. 

The born blendc in the dark-color cl eet·etion · i · partia lly icli orn orphi · and 

partially allotriomorphic, with the latt r tendency clec ideclly th e . trong r; that i.-, 

cry -tal form · may bv d v 1 peel on part of a ery.-tal while the r .'t ha · a very 

irregular outline. The ob. crvcd fo rms ar the u.-tomary unit prisu Rnd clinopinacoid a nd flat term ina! fa ce . The color i.- mostly like that of the greeni h·brown 

horn blend of the dacit :,; and th e ab ·orption i b ~ .c ~t. The cu. to mary color:,; in 
PLATE XVII 
THIN SEGJ.'IONS OF MI "ERALS I " ECRETIONS IN DAGr.fE. 

FIGs. A, B, and C.- Magnified re pectively 40, z-, and 15 diamcteri'. ~11 from p cimen :ro. 145. 

From a dark-colored seer tion a)nona the dacitic ejectamenta. how spon<>iform plagioclas crystal 

inclosing deep-brown gla imila r to that compo ing the groundma , from a dark-color I secretion 

among the daciti c ejectamenta. e page 126. 

FIG. D.-Magni fied 1 diamete1 . 'pecimen N . 144. Frou1 a dark-colored ecr ti on among the 

daeitic ejectamenta. how. · a grain of hypersthene inclo ing numer us plagioclase grain , and two 

irregular grain of olivine marked 0. ee page J ~9. 

FIG. E.~Ma nifi d 50 diameter . pecimen No. 14 . A Jjght-c lorecl, granophyri s cretion 

among the dacitic ejecta menta. . bows crysta l of plagiocla e with fr·inge · of . pongiform sa ni line 

containing inclu ion of brown gla and r emblin" granophyric in t rgrowth.·. 1llu tJ·ates a ection 

a seen in polarized light with eros. ed ill ol , the glass appea rin<> black. ee page 1:36. • 

FIG. F.-Magnified 10 diameteJ. . pecimen No. 142. From a dark-colored s cr tion among the 

dacitic jectamenta. hows a large crysta l of browni h-a reen hornblende inclosing crystal of bypertbene = H, plagioclase = P, and magnetite. ee page 129. 

128 
U. S. GEOLOGICAL SURVE'r' PROFCS IO~AL PAPE'R NO . . 1 PL. XVII 

(A) 

(B) 

(n ) 

(C) ( F ) 

THIN SECTIONS OF SECRETIONS IN DACITE. 

DA. l'l':E . 129 

thin .·cdion fo r ray.· vibmtirw pandl l to t ho v r t ital axi,; i:-; a deep b rowni:-; h g r een 

to g r ce ni.·h brown, in :tccor cl an · with· t b t hi ·kn ::;.-of tlr section. Th :th ·orpti on 

and p lcoc hTo r.- m pa ralle l to b are almo:-;t xactly like t bn.t pamlle l to .c, with t he 

ttb:·oTption u:·ual l . a, I itt! Htro rwcr r aralt I to h than to .c. ln No. l+5 t hil:l lllinoral 

appear:,; to be unw; ua lly scarce and th c.:o lor in rn.y::; Yibm ing para.ll ol to c. a deep 

hrown i::;h r eel. Tuo,;c parall el to b ·an not he dot nni ned in tb i;; H etion. 1" 0 • 

l-1:1 there is a peculiar ming-lirw of tb r 'ddi,· h ' itb ~e g reenis h-brown color;;. 

i\l o~'t of th e '~'.)'· 'tub b lo ng to tb g-r 'Cni :-;h -hrow n vari ety but oth ~' ~" ha v both 

colo rs shading- in to each oth r on t h .-amc cryHta l. This sha lirw of colors oc ur.-

o n perfectly fre. b e ry tal. ·. Jn fad a ll th ' hom blend erysbtl:s in the·' Hp cim ' llH 

are ab.-olutely fro. h a nd d not show any tendon ·y to r0sorption or Lo the d Yclopment of bb ·k border.-. The :din ·tio n a n o-le of the born b londe, aH mca::;urccl on 

clcantgc fmgwe nt..,; from No. 1±3, i.- '"' to the \'CI'tical axi ·. Tho optit;}tl axial p lane 

l·ie::; in th plan of g reat .-t ft nd I ast ab::;orption: that i.-, in the p l:Lil e of the t l inopinaeo id. A .-ection of t bi. mineral in No. 1:1:3 that gm·e a. prism angle of l04:o, a:-; 

m a: urcd by th traec f tb pri. ·m fa c::; with the p lano of tht' .s' ·tion ga v <L 

hi · etrix in th cent r of t h fi Jd. 

Th ' ho rnblende of thcs .-c -r tion · doc::; not ·ontain inelu i ns of ght::;s, hut 

it i::; ' c ry apt to ·ontain irlClu. ion.- of tb oth r plr enoc-ry:-; ts :-;o a,; HOIIIotiuwf-' to ~ 

filled with them, som what afte r the manne r of in lu ·i m; in the horn hi ndc o[ the 

c rystallin e :chists. F ig. F of Pl. XVII g iY .- nc of the.-e hornbl end e cry:-;tlcds 

·onta rmng- in lu.' ions of hyp l'l:ltb n pla.g-iodu.-c, a nd magn tit . ln oth r en.-c~' 

augite nmy b' .- en i n ·lo ed in horn blond . The, e mineral. wh n t hus indo::;od 

may ha,,- idiomo rphi forms bu th y ar mor apt to b hy pidiomorphic. At 

1 a-t tb -ir form are not alway. so sbm·p a.- wb n th .)' occur cmbedd d in t h 

g la.-.- ba · . 

H rn bl nd o cu r · in mu ch larg r ·rytaJ · than do tb other min ml::;. lti.-

vcry flu tuatin · in qu:.~ t , b ing very paringly d v loped in o. 1-r, or at lea t 

in t h thin ution pr par d from tbi pecimen and extrem ly abunda nt in No. 

201lb. Fig. B of Pl. XVliJ r pr od uc •s a portion of thin :ection of ?\ o. :Wllb, 

showing the r lativ abundanc of th e bomhl endc. This i.- not a fai r a \·erage of th 

who! s etion. but show.- the hornl.J I nd ·om what mor ' abundantly thftn in th 

r c ·t of th .- tion . Th c ry ·tal form i · unu:-;ua ll y .- burp in this ro k. 

H y pe r.-th ne i · by no m a n · .-o abundant a.- horol 1 nd , n r does it occur in so 

la rg ·ry ·tal' . lt i · 111ore inclin ed to id iomorphic fo rm · hnt it al ·o ·how.- ~L tendency to ·ontain inc! sure · of oth r miner a l . F ig .]) of Pl. XVII o-i,·e a ·tion of 

h_n r::;th n f rom o. 1-±± containing in lo urrs f plrwiocla ·c and two irregular 

rnclusion.- of olh·in . This is xc ption,d. A.- a rnle hy per th ne i ' older than plag ioc lase, and even in t hi · a ·e tb in gular fo rm of tb plagio ·Ja, e cry tal,.; indicates 

lht~5 o. 3- 04'-9 
1130 >E1'1WG ~APRY <.W J{,A'J'JO{, LA KJ<: NATI ONAL PA H.K. 

that their pe riod of formation d id not g reatly precede that of tb hyp n<th n . The 

opt c~d p ropertirs of t he hyprr.· t h no arc in no re 'P<' ·t difJor nt. fron t what may be 

see n in the hypc rsthcnes of the J;u·ite~. 

Oli vim• is to lw fo und ve ry sp<trin o·ly dcv' lop'd <L nd ;dways in o~cd in c itb r 

ltyp orsth 'n' or horn blende. 

A twi t' is lllu ch k:;s t·ommo n t han h. 'p orstlt enc. It has a pn I -g ree n i.- h tolor <Lilcl 

IHt t li ttl e pl cochroi:-;m. J.t is youtw ' I' tlw.n plngi ('Ia • .,;' a nd hyp rsthenc a nd o lder 

t han horn hlcnd . I t oceurs both in roun li .- lt g rain.- an d in fa trly dcv lop d cry.tal.-

siutilar to tho.- in the dacites. 

Th0 orJ.c r of c'l'yst<Li li z<ttion of the phcnonyst · of tbe::;c se ·r<.'tion.- i.::; in gene ral 

n,.; follows: 1, ore· and apatite : :2, oli' in c · 3. hypcr::;tb no; ±. p lao· io ·hve; 5, a ug- it ; 

G, bo rn l>lenclc. .\.t ti nt 's t he plag io ·la.'-'C app a r.- to chang ' plac ~ with bypc r.-thcn ' · 

That t hcs clark-eolo rctl bolllhs a rc in reality ;;cer t io n::; fron t the da ·iti · mag-rn;t 

nmy fa irl y we ll hC' cst.ab ltshcd hy the simila ri ty of t.bc minora,! · nt nts wi t h the 

phenoc r_L ' of b dacite . Thi · i.· mor - c pccially true of hornbl nd , whic·h, with 

po:sibl_v ne minor exception, i ab. ohttely foreign to th andesites a.- well as to t h ' 

ha,' alt.- of Cmtcr L<Lk . hut whi hoc urs with t l sam tolor · a nd othe r p rop rt ics, 

although ,·cry parirwly , in nearly all the t.bin ·ections of da ·it .-· ;;tud ied . T h<tt 

tb . :fragm nt.- w rc C' r u1 ted at the sam time a.· the dacite. ~ ind ica.ted h_y t hei r 

occurring with t it pumice of the da ·ite", nncl mo r ' irnme<lia trly hy th finding o f a 

homb in t he midst of the pumi c ou.- dep sit .-o uth of Lhto H.ock co n: i.-ting· in part of 

p umice and in part of th is IJhtek, g la..-sy. h rnhl enclic ro k. 

Tbc ehemica! tL nal_y.-i.- of No. H:3 wi ll be found on page 1-:1:0. In pitc of tb 

,-idc.nt r labonsbip of th '- c lark-col red "ccr·ction. to the dac ites the Ln l_v · shows 

a marked dif:l'o rencc. Tbi.- i;; p<trticularly noticeable in the hLr o-c amou nt of limo and 

in th co u c;;ponding clecrca;;c in th' a lkali ':-:. Th ana]_,·sis in fact, b an:; a clo.-

r ,,. m bla.n ·c to the analyses of the Ill Ore acid ba~a ts No:;. 15 a nd 18D. 

LIGHT-COLORED (H'l.ANOPHYHI ' SE RETIO ' . 

The. e arc not to be con id r ed cr tion.,; in th e s n · t hat tbi. t rm i.-fr eq uently 

u.-eJ. in cle1<c ri bing- th accu mulations of older min ra J.- t ha t fort11 dark-colo r d i nclusiom; in ig neo us rock · wh i ·h i_. the :en:;c in whi ·h tb word i:-5 used in dcs<.;ri bing 

~Lho, c tlw dark-co lored seer tions. But ratb r, t he · light-co lo red sec retio n;; appear 

to r pre:ent loml y~;ta lliz at .· or d iffer ent iatio ns of tir e sam min •mls t hat arc to 

e~; en in the dac ites in g neral, but .·o aggr egated togethe r as to ttppcar in totall y 

d iffer ent .-tru ·t ural r e lation ·hip. . Tbr.y have not heen fo und in pln.c. o r inc l'o,:;ed in 

a:tritr hut only as loosr fnwmcn ts 0 1' honrbs on t hr . urfaer. 

1 o. HH i.- a sma.ll tmgrn cn t ahou t ~L n in<' h ;;quare t h:tt fo rill eel pu.rt of <L eon g) mPrnt overl ying th e snutll lac itc liow in nnC'd iately above (Jrotto Cov . Two oth r 
PLA'"TE XVIII 
PL TE X \ Ill. 

• THIN E O'.riON ' 0~' SECRETION ' IN" DA 'ITJ.:. 

Frc:. A .- Vitrophyri c dacite and secretion in th e same, from Llao .Rock. :'llag nified .J. diameter . 

,'pe im n Ko. 102. A photomicrog raph in white lia ht. On th e left i th dacite, c n isting of a 

gla .· with a multitude of augite mic rolite . n the right i the ecrelion, comp s d fa f It f plagiocla,e laths and slender pri m. of re ldi h-brown hornblende, which appea r n ear! black in the figur -. 

The int rsti · ~ of thi fe lt ar filled with light-br wn <> Ia, s. The lack of a sharply defin d lin· of 

junction l.Jetween tb rock and these ·retion i characteri tic. e pages 105 and 110. 

FrG. B. - .A photomi rog ra1 h in white light. Magnified 20 diamet ~ . . ' pecim n No. 20Ll b. 

Hlu. trates th abundance of reddish-brown hornbl nde in o n of tb e dark-c lored .· c-r tions. ~fl 

page 12H. 

FIG. C.- A light- ·olored g ranophyric ecr ti n from th rla(;itic ej ctamenta. iagnifi d 20 diamet rs. • pecim n No. 151. • 'how · a dark-col r l brown la~ · and pongiform mantle of sanidine 

a r und plagioclase. • 'ce 1 age 136. 

FIG. D.-A ph otomi crograph in polaril\ d light with ·ro eel nicols. Magnified '6 di;uu et r'!:!. 

• ' hows an enlar d p_o rtion of fi ' · ', gi,·ing an individual plagio ·Ia. grain with mantle of spon"iform 

anidin . The black po rtions a r·e glass. 

132 
U. S. GEOLOGICAL SURVEY PROFESSIO , AL PAPER NO. 3 PL. XVIII 

(DJ 

THE ME:R!OfN GRA VURf CO . 
• 
l)A l'l'F., . 13R 

fragment. from thi.· . amr conglome ra.t hay a.lreftd}~ he n de. rihed. Th ::- ar' No. 

139 a pumice fragment ront.-'Lining murh hornll nd , and o. H5. onr of the dnrk-

·olored eer etions. Thi. · a ·so ·iation would ugge ·t thr :-;a me .' our ·r a:; that of t be 

dark-colored ;oec et on~. [n th band . pe im n tbi:-; appenr,; to he :\ fairly roar · -

grain cl, holocry:;ta llin e ro k of v ry light olor and omp ~ed of !L whiti ·h, gla . y 

appearino· gnwular aggr gate dott d with , mall, dark- olored arain ·. It i,.; fll li tr 

brittl and crumbl e in the finger . In thin eetion th e rock is .· 11 to co n ist ma.inly 

of plagiocla. ·e, whi h c n titute: p rhap one-half of the' hoi or a littlr lr!'lH in 

addition to whi h tb rear hyp rsthcne, augite bomhlend and a very littl biotite. 

All these fenomagn sian min eral.- together form bnt a . ma.ll part of tb wholr. 

They nrc perhap. a littl mor e abundnnt than i.· u ' ual in th d1trit :-;of 'ratrr Ln.kr, 

hut not markedly so. The r . t of th rock form:; a .'1'ort of g roundnHl.Hs r ithrr :-; urrounding the. e older min eral: or filling the paces hetw Pn them wh reY .r tlH' phrnocry are cloRe enough to touch ea ·h otb r. Thi · groundma ~ con:-;ist:-; in part of 

a deep brown and per£ ctly clear gla. , br;t mainl ' of a beautifully ·harp and haracteri ti granophyric or mi crop gmatitic intergrowtb of quartz and sanidin r. Th 

pre. ence of quartz could be demon trat d by oh ervation in conv rgent polariz d 

Ji o·ht, in wh i ·hit g ive the positive uniaxial CTO ·,a well a hy the mor r eadily 

ob. erved properti s characteri tic of th min ral. Tn tb ea of ~<ftllid in the 

d mon. tration i.-not complete, but i · ba:;ed upon the following oh' ern.tion ·: Jt i: 

p rfectl.) clear and colorle and co n~•in no in clu.'ion · except minute a ir ea itiN;· 

both tb r fracti\ e p w r and th doul>I r fra ·ti n ar I s tbao in th acljn.<· nt 

quart11; it ind x f r efm tion is le: than that of the HLUTounding baLam; in conv rg n polariz d liaht it aive ' a biaxial image; it is ntir ly free from twinning 

striation or from 11onal . tru tur ; this . anidine u ually form ' a mantl ar und the 

I lagiocla cr ' ~~J., o that itb r the outer part of the. anidin mantle is .intergrown 

with quartz in gTanopb:ric fashion or, mor u. ually thi - granophyri int rgTO\\'th 

beain , .lo e to th plagio la ·e dg , with little r no free mn,ntlr growth vi. ibl e; tb 

ontra -t b tw en the plagio la ·e and the a.nidin mantl i. u:;ually rath r sbaq ; thr 

pl~bgioela r very fr qu ntly ·how.- no twinnin · ttri1e, but the one ntrie 11onn,l 

.-tru ·t.ur i. n.lwa,v · vi. ibl , wher as th ·anidin manti i:; entir ly fr from a ll 

twinning fUJd cxti ngui. he. , imult.-'Lneou. ly. Be<' ke':-; meth d for determin ing th 

index of r fra tion, a. compar d with that of anadn, b,1l ·am. by focu~ing .· barply 

on the dae of a ry. tal in conta ·t with bal. nm and th n ob erving the movem nt of 

th white band upon rai ing or lowering the f lL' , wa · found very applicn,ble in 

tudying tbi anidine mantle. Wher a cry t.'Ll of plagiocla wa brok n and in 

onta ·t with baJ am it wa:- invariably found th~bt the portion of the cry. tnl that 

showed twinning or zonal tructure hn.d a higher index of r fraction tbnn l)al. a111 , 
134 PETROGRAPHY OL•' ' lt A 'l' KR LA Rl•: N AT10 A] , P A HK. 

whil th e out r unt\ inned, and unhanded portion was lowc r in refnteti,•c pow r 

than I n,l am. Tlw . ah1c method i r qmdl.y app lieablr in this eH.:s in in o- ui bing· 

hetween ·a nidin and quartz. 

\Vhm.·cy r the quartz or t h '}Lnidine come· in ontn t \\'i t h t he bro\ n o·Ia. s base 

it br ak np at tlw dge in to an irregul!trly lol ccl fringe, with th e r oundi h lobrl:l 

in t.Pnvoven or in teroTown with the la ~ in fL way .·ug·ge ti of th oTanophy ri C' 

intrrgrowt hs them. eh ·e,;. This interweaving of o·la . with th frino·cd cdg .·of th r 

crystah; i. :o mnch more heau tifu lly de,·e lop ecl in oth r spr imcns w h sc ci t Hc ri ption 

foll ows that n, deta"il d :les ription of tbi. phr nonw non will lw po. t] oned fo r th 

prrs!'nt. The qna rt;, i.' not pre.'ent excep t in thesc g rnno1 hy ri c }lgg-rcgatt'H. It 

inclo. c: a ir ca\ iti : imila r to th ·anidin c. 

The plag ioclas in t his r ock do : not havr a ·ha rply devol p d forms a · in the 

da ito:. Tbi: is true even when the surrounclin o· :ani clin man I is disr egardrd. 

, ecti on . . ·nitable fo r d termining the extinction a rw l .' w r not fo und bu t : u h 

extinction ang l . a .. wer e noted ind ica.t a I a:sic plao·io Ia e. Thi furthe r 

corroborated by the fact that the plagio Ia v n at tho do-e ha a n ind x of 

refraction gr eat r t han Canada bal am i .. g r ater than 1. 540. f ' " inrlosur(' · 

of brown gla · with gas bubble and a!. o . mall a.patite pri m we re not d. 

The fen omagne ian mineral: all have poorl. develop d f orm. . H.vP r ·th n 

and aug it occur mo tly in . mall pri: ma ic g ra in ·, om : irw ly but mor e commonly 

in more or le pa ra llel arrang d g roup ·, tog·ether wit h magnetite ftn cl hornb l nd 

and with da rk U'l' ni ·b-brown ui tite. Tb horn blende ha.· a g re ni h-brown olor 

and occur: q uite abundantly in longi::;h granular or pri. mat ic individua ls. Biotit i · 

, ca rce, but it pr . ence i the mor e noteworth y a.. it appears toll<' entircl. wanting 

in th da ite proper. 

The writer ha not e n a full de cription of rock i.mila;: to thi , hut P rofe ·sor 

Ro. n hu ch a make· bri f r ef renee to ·everal qui te a nalogou oc urrence · in I c land, 

t he or iginal de cription. of which ar not at the tim of p r eparirw tbi pap ·r 

n c . : ibl to tb writer. In the ·e I celandic rock whi h oc ur as inclo. ure: in basalt 

and in loo: fragment:, ar to b :een a . . imilar mineral aggregation with plag·iocla><e 

C" ry:ta l: smTound d with ortho Ia mantle · and g ranoph,vrit oTowth .. 

\.mong th 'rater L a.k rock. collected in 1 3 tb r ,-u·c fi v : pecimcnR, o:. 

1.47 1-1- , l-:1:9. 150. and 151, wbi h a.r e labeled a. being jected vo lcani · f m gm ntl from the top of th divide h tw en Sand Creek and A nna ' r e k, near the 

:outb rim of Cmter Lak . The · fi ve p cimen. ar c clo ely analogou. to o. 14G. 

ju ·t d c rihed , n, nd in one or two_ ca:e practical ly id ntical in a ll e · ·ential poink. 

o. 149, fo r in:tan e, v r y lig ht co lor d , el i ·tin ctly granular, and ve ry friabl e. 

It cliff r· lightly in olo1, in that the :feld par" have a eli tinctl y pinki ·h ·olor. 

a i\lik roskopische Physiograph ic, 3d dition, \'ol. Tl, 1 9G, p. 590. 
DA JT.R 135 

On th other band o. 1± 1 ' ery mu b da rker and look. a thouo·h it wrre 

composed abont qually f a white granu lar f ld. par and of h lack o·hv, . 

nder the micro:cope the practical identity of <111 of the ·c p imen. with 

No. 1±6 is very ovid nt. There arc the sam l1l<tro·inal growths of anidi nc arou nd 

th e plagioclase cry:tal , and tb sam gmnophyri c int roTowth: of 'n,n idine with 

quartz. The d ep-brown gla ~ in ter weavino· with th sanidi n i. n,l o pr · nt, hut 

in nmch o-reater fth un dan in two or thre of th e ·1 er.imens. Th most -trikingd i ft'erenc hetwe n th e two occurrence · is in th fa ct that both horn blendc and 

biotite arc totnlly )a(·king- her e. Owing to better pr pared thin section ' as w 11 :ls 

to th e opportunity to study . ection from a number of similru· although not qu ite 

identie.-<tl spe ·imens, ome of the feature' not ,·ery cl arly ob erv ed in o. HG 

can be pre.- nted her e with greater full ne ::tnd certainty . 

The p lagiocla ·e doe · not, upon the whol appear to be quite . o ba i · rt is 

th e ,·ame min eral in th dncites. Twinnin o· triation · ar abundant and di.·elo. c 

the presence not on ly of th albite law but also of the periclin and 'arli;bad Ia w ·. 

But se tion uitable fo r det rmining th - maximtlm symmetrical extincti n :tnglc. 

do not eem to b common , which i doubtles due to th fa t that th ratb r 

large average .- i:r.e of th cry tal· doc. not aliow man y of them in a,ny one thi n 

. cction to be ut in the right dir ction. The large t extinction a.ngk m a ·nr0d on 

a · ction cut at right angle · to the albiti c twinning phn was 27° in the crntral 

1xnt of the cry tal. A all of the plagioclas ha a w IJ-defin cd zonal t-itrnctm c 

the rmtrg-in of th crystal is ne es ·ari ly mu ·h more acid. ·unlly the · ction · 

that g ive :-;ymmet.rica l extin tion g ive very mall xtinction nngles, even on th 

interi or of th e ry ·tnJ. Thi i o often th ca··c as to indicate that at lea,·t . om 

und ob~tbly mo t of the plagiocla e i ligocla · . Thi.- ·uppo ition i · further 

horne out 1 y tb fa t that .-ncb crystals, vh n broken o a to bave Canada hal ·am 

in conta ·t with th plagiocla. e ar e n to ha' e an index of refraction a,lmo ·t 

identical with that of tb bal am, which would indicate a feld par a1 out on the 

bo1·der of oligocla and ande in . While tbe index of refraction thu. indicates 

tba,t ."ome of the pln.gio la::;e, even in t.he in terior of the cry tal, is hard ly 111 0rc 

basic tha,n oligocla c in a,ll ca ·e · wh rc the ob ·e1Yation wa made the oute r 

portion of th plagiocla ·c bn thi: deg r ee of a idi ty. It . eem mor than likely 

th~tt tb rc a r two l in d·· of plao·iocla ·c cry ·tal present, a fairly ba ·ic a,nd not ve ry 

abundant va riety and a more commonly d veloped and pre ·umably young r \·ariety. 

But in any case all th e plao·iocla e ·ry tal · have the mantle of sanidin whi h, 

wh re a gla s ba. e i very abundant, or wher ever tbi g la ba ·e come into 

co ntact with th' manti , i very r markably fringed or lob d, o that the roundi: h 

feldspar lob . app ar to b ir1t rWO\?Cn 'vitb th gla · in a mo t intri cate ' ay but 

;v hich, in the ab en e of a urrounding glas , form with quartz a beautifully di.-tinct 
136 PFT.RO RAPHY F CRATER J"AKR ATTO AL PARK. 

and rather on.r:-;ely d v loped oTanoph ri c agpTegate. \\ hi le thc:c mnro-inal 

g rowth around the plagio In ,, t ry. tnl. may be :-; en a round v ry indi,·idual 

plagio a~ they do not nee · arily entirely ·urround th crystal, nor d c th 

fringing mantl have co nstant width. In thi. re.'p ct th ruantl .i • ve rj irr o-ul<Lr 

and ven crrati ·. A,.; nbovc tat cl, the interweavirw of th brown gla . with the 

f ringed sanidin o·i,·e: almost exactly the ir 1p r ·ion of the granophyrie g rowth 

when .·cen in polari'zcd light, except that a portion of the in t rg rowing : ub mn 

r mains extinguished when the : pecim n i rot..'Ltcd. E ,·cn in white li o·bt t hi: 

re:cmhlanc to g ranopby ric g rowth:; i: oft n pronounced wh en v r the g la HH hns 

an unu ·mtlly lig ht color, and thiH i,; th e case in those Hpccim ns in whi ch the o-ln:s 

ba: i1; not ~Lbundftnt (L±!-l), or in whi ch the . crtion is unusual!. thin. Furth r 

thii:l rc: mhlanc is made :;ti 11 mor e marked by the fa t that fLt t im s th g la: · 

that app fLrs in t rwoven wit h the feld::;pftl' bTeftk: up into recbtno-nla r or othcrwi ·c 

polyo-onal form. with more or los. pamll l a rrang m nt. Or, to xp rc · rt in 

another way, th ·anidin margin develops in to a k 1 to n g rowth with the brown 

gla:' · ba e tilling th - interst i . Tb n:triation: of tru ture that ar produ d in 

th e e mar o-inal g rowths, owing to 'On ·tantly vary ing amoun of gla and th 

co n qu nt app arance and disappearanc of r eal o-raoophy ric g rowth fnirl bafr1e 

de. cription. It would requi re a large numb r of dr<Lwing. or photograph · to g i,·e 

a fair conception of t b se al mo. t fa ntastic -tructur . . A n ffort bn be n mn.de 

to reprod uce some of th e mo t strikino· ffec in fig. F of P l. X TI (p. 12 ) fi o·: . 

and D of Pl. X TIL (p. 1H~), and fign. A and B of Pl. XIX (p. 1:3 ). 

The amou nt of quartz pre eot appear · to be inver. ly proportional to the 

amou nt of glas ba e. Where much gla i · pre ·ent it i: not in lin d to fo rm 

granophyric g rowth but to occur in rather i. olated, roundi h, or irr gular grai n . 

!though it rna have very ilTegular ·outline: it doc not br ak up in to lobe · or 

fringe· at contact with th glal:; ·,as do th .:anidine, at I a:t not to any marked 

extent. In the mor thoroughly cr.v. tal lin e pecim t1 and th rcfore mo r 

thoroughly oTanoph) ri va rieti , the quartz eldom occur in : parat g rains. 

The sanidine i ' not ab. olutely confined to t b g ranophyri margin · but abo 

occur · ve ry :::parirw ly , ru do : th quartz rn : pn.rate hut irregularly form d 

ra in . 

[nclo. ure 10 th central portion of the plagio la are not common. Gla. : 

inclusions app ar to b entirely wanting, but not infrequently a cry ·tal may 

·ontain small augite grain ·, or individual g rain. of magnetite or prism of 

apatit . Mi nute air cavities, however, ar very abundant, both in th plagiocla e 

a nd in the urrou ndin o- fringe · of quart:>. and :anidine. 

Tt . hould , p rhap , h added that no add itional r ea on can be given for the 

pre ence of . anidi ne in the e sp cimeo than tho e alr ady g iven in the de cription 

of o. 146. 
PLATE XIX 

187 
PL 1' E X I X. 

'I'fTIN • F.CTTO OF RASA LT .. AND O F . ECRF.TTON I ' DA TTF.. 

FJG. \ .-Light-colored •rano1 h y ric ecretion from the dacitic ej ·tamenta. Magnifi d 4 diameters. 'p cimen Xo. H . .\ photomic-rogra ph in 11·hite light. , how lhe \'Currence of dark-br wn 

glas., pla<>ioclase, spongifon11 sanidine, parallel growing prism , and grain of h y[ rt>thene and augite, 

al ~o a little ma<> n tite. , ee page 136. 

FIG. B. - Light-colore<i "ranOJ hyric seer ti n from the dacitic ejectamenta. Mag nified G cliamet.e rs. • 'pecimen o. 149. A photomicrograph in ll'hi te light. how. a huu<il e of pamllel a.rTRng d 

priRrns of hypersthene and au<> ite, which can not b eli. tingui hed from each oth er in th ph togra1 h. 

Rc<' page J3!J. 

FrG. .- i\fagn ifi d 4 diameters. pecim u No.· 2029 (private ollection of H. B. Pat.ton ). .A 

photorni('rograph in ll'hitc lig ht. Show. tbe inte1. titia l tru ·ture of. orne of the basalt . 

Fro. D.- Basalt, Timber 'ritter. Ma"nifi d 4 diameters. 1->p cimen No. 16!). 

graph in ll'hi te light. lllu tratcs the fluidal-interstitial . tructure of orne f the basalts. 

13 

e page 14 2. 

A photomieroSee pag 149. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER NO. 3 PL. XIX 

(D) 

TH( WUIIDfl'f OIIAVUit£ CO. 

D TTK . 130 

H y persthcn a nd a tw itc ar c hot.h ve ry abundant. 'Ne ither of tlwm oc·r ur in 

the ·u. tomary id iomorphi c c'l'yst.<th; but cit h l ' in p rfectl.r irr g'llla r grai n.' or -

whi ch i.· gcn rally t he r\a~c in vari on.· s hap ' d aggrega tes. or 111 0r t'sp (' ially 

In lu ·tcr. or b unchc. of loo.· I.)' aggT 'gat'd rtnd pftraliPI-growing- rottn di:-dt and 

r a.th r .·le nd r pri mati · g r ain". Both of t hc::il' min ra],.: assum(' thi.-; snlll ' fo rm 

nnd usually both of th m occur together in pamll I g rowthli. A II oncPi l'able 

~u at ow· ma.r h ob. e n ·ed between isolated incl i1·id ua l. · of h vp crsthC' ne r an O" itf' of ' b 

t he shap jn ~t mentioned and parall el ao·g regates of t h<' :amc t h:tt ontA in hun d r<'d>< 

of th small prismat ic grain,.;. om id a of t hi,.; oceutTcnc·e may he dNi1·NI 

f rom fi g-. B of Pl. XIX. H y per.- th<' n ><<'0011; to b<' the mor<' abunda nt of t h , 

t. wo. In color the hypersthene i not qui te :o da r k ac it iR in the ord ina ry 

dacite · of 'rater .~a . PI cbroi: m, t he r for . ean not r<'acl il y b sc n in s uch 

·cction: a: a r c n ce. a r.1· for p rop r .·tucl. of t he aggr<'g·at<'s. Th a tt g·ite ap1 carR 

almost ·olorlcs in t hi n se tion. 'I'Vit h the. two I y rox<' ll <'S t hen' is ('Onstan tly 

ft.-:so ·iated ro dc abl mao·nctit , whi ch t·cur,.; most:y in ye ry rninu t gra in;; 

inclos d in the in diYid ual p: r oxene oTa in- or elttRtC'r d with lhPm in t·lw:><' 

huncheR. 

The ch mi en! a naly i · of I o. 151 \lriJI b fo un d on page 1+0 tog the r wi t h th e 

other ehC'mical a naly e ·. Whil . om what morr bai>i tha n ttr t he dacitct-i p roper, 

t he a naly:is of hi p cimen will be s r n to ·om paro fa irly ·l osc ly with thnt of 1 o. 

1l+. Theex:cc :-;of lim may perhttp:;b attri hut.<tb lctotheabundanc<'oftlwp,vroxtrw. 

Jt ean ha rdly b d ue to t he r lftti1· ahun dancc of t b<' fe ld ' par, a.' the plagioelns<' 

p resent do('. not app ar to he pa rt i ul arl) ba ic, and t he ,;u rn of the ;tlka lie,.; p rrs nt 

is rathC' r le.' :-; t han i · t h ca with th dn.cit<' who ·c a na ly::;e::; ar o·iv n. 

Tn <·o rw ln:ion w may ·ny that the ah · lute fr e:b rw of th . e pecimenR would 

'<'<'Ill to pr d ndc t he p ili t~· of :t . 0 ·onda ry orig in for t he a. oph ri · '"rowth,.; . 

. BCm<:TION, WITJI HA AL'l'-LI:KE THU T .E. 

I n add ition to t h ab ve-dC', cr:l.> d ·ecr eti ons t h r r ma ins a. p im n coll ected 

in t he bottom of t.lw 'un Cr<'ck Canyon and a.lrcacly ment ion<'d on 1 ~1ge 123, t hat can 

not ho d a :-; ifi ,d wi t h any of t hese va ri eti . The . pec im<' n i n guo tio n (123) has 

n. g- ~:d t color nnd i · mth r· fi no grained, hut i · distinctly g mnulnr a nd porous. Tn 

t hin s d io n t h<'. t.ructure appear•" at fi r:-;t g la nc(' to h d istin c-tly basaltic. wi th darkhr wn g-las.· in tlw }tng ulnr in t r ti c::; form d by th.c int !"ections of mtlw r short, 

thi ck- t plao·ioel:ts lnths. Roth hy pe r. th en and augite a bound and CCLII' in itTcgular O" rain · not di. simil a r to th e ha' a lti c pyr oxen ' , al o in long, slend r p rismatic 

form ·. In addition to the. e mineral., horn blend in da rk r eddi h-brown g mins a nd 

pri. m j q ui te abundant, a nd magneti te in occa ·iona l bla k g r ain. . 0 ·ca. i na lly a 

phw iocl::tsc or hy per t hen ry. tal assunr ,.. . om what o·(' r fo rm and appea r in t h 
140 PET IWC+ BX PRY 0 1r '1'tA'l' lm LA KE N ATf() AL P RK. 

role of n. I h noc ry;;t. . "hnJ. app a r,..: to he dark -brown gln,.;:-:: in ·lo. ing nd r n.ugito 

mi roli t -.· a nd fillin g th e intrr;;t.iccs lwtwe n t be p lag io la · lath,.: i.· :' n in 1 htri d 

lig ht to b ,.:ma ll. :1 lw ruli ti · y:ta lli ~nt :; . Tn ;;pit £ the gen m l truttur t his 

rock iH quit cl iff rent f rom any of t he ' rater La.ke ba ·alt.-:. lt as. o ~ia,tio n with 

dacite. and tb c p r ·en e of auunclant hornbl ndc, a.- well a. tb pheruli t i base . lead 

to the eo nclu. ion that th is is in r n.lity n. . ·r tion in a clftciti c magma . 

n in ·lttsion in n, dacite d ik b low L lao Roe k. de ·eribcd on pag 122, 1. con-

·idcrecl to h0 a ;;imi lar occurrcnc 

CHEMICAL ANALYSES O F DACITE S . 

The fo ll ow ing analy cs wer e mnd c in th laboratory of th e U nited , tatr. 

GeoloJ?;ic-al S urvey : 

,' (.) ~ ·- -- -- -- -- - - ----- -- .... . . . ---

Al"O, .. . ... -- -.---- .. --- -- ---- · · · 

Fe"O" . _ .... -. - --.. --- . ---- ---- ---

Fe 

-:'llgO ... __ . __ _ • . . ---.-.--.-----.- -

OaO _ .... .. -...... --.. -----------

:::\a.,O --------- ----------------- --

K" ----·----·-------- --- -- ----- -

Tf" .. --- ..... -.-.--.-.-- .. ----

H2 - -------------- ----------- --

'1102 .. ----.------.--- .. -- - - .-- ---

7.r01 . ... .. ..... -- - ..... -- -- . -----

001··-- .. ..... --------- ----------

.P,Or,-.--.--- ..... -.... ------- ----

' I 3••• • ••••••••• ••• •••••••••••••• 

(Ana ly• s by H. 1\. 'tokes.] 

102. 

70. ~7 

14. 3 

1. 35 

] . 25 

. (H 

2. 12 

5. 07 

2.6 

. 0-5 

X one. 

. 13 

Xon. 

113. 

15. 1 

1.7 

1. 09 

. 7-1 

2.27 

5. 1.5 

11-l. 

I 

6 .17 

].'\. 60 

2. 31 

. 9-1 

I. 02 

2. 76 

5. 15 

2.46 

. 09 

.45 

. 54 

X one . 

Kone. S on . 

. 131 . 13 

Xon . Xon . 

130. 

1. 02 

.+ I 

I. !)9 

5.0 

2. 4 

.o6 I . 22 

. -11 

.0-lXone. 

. 10 

)lone. 

1-l-3. 

--- - 56. 5 

l . 31 

2.88 

3. 15 

3.92 

7.20 

8. 9 

1. 23 

.16 

. 9!i 

1.0 

n . 

. 22 

Xon . 

151. 

67.4 1 

15. 76 

l. 

1. 7U 

]. :{5 

3.::!6 

4.!i ~ 

2.36 

. 09 

.54 

.fi6 

r'on . 

. 12 

0 1 ................... .. ..... . ... . . 11 ~ Tra ·e. Trace. 1 

... -- .. -- . ... - -- .. --

1" .... ...... .. .. -- -- -- ------------

r 20 ,. . . --- .. . -------- -------- ·- -· 

NiO ------------------ -- -- --- -- --

~'[ O ____ .. -- -- ----. ·-- -- -- - --- · · ] 

Ba --- ----·------- --- ----- ---- --

,'rO . . . --- -·- ------- -- -- ---- -- -- --

Total ____ -- -- --_---·- __ __ ___ _ 

l ntlet. 

X one. 

None. 

None. 

'£race. I . 08 

. 02 

Trace. 

99. 

one. 

Non . 1 

'.rra e. 

.0 

. 03 

Trace. 

99.97 

nd t. 1'raC'e. 

one. n . 

Non . 1 Non . 

None. 

Trace. 

.06 

.0:3 

Trace. 

99.7 1 

None. 

Trace. 

. 0 

. 03 

Faint tr. 

99.63 

"Or. Oa = .CI-1. \\' hether present o.• or 80, umletr rmined. 

:o;o-r>:.-O=CI. 

~o . 

To ne. 

Tra ·<·-

.0-1 

Trace . 

a. 02 

Non . 

Trac . 

. 06 

Trace. 

Tra ·e. 

99.81 
BA ALT,' . 

No. 102. ll y p '' th enc-dacite, ,-itrophyric t_,·pe, sou th edge of Llao HoC' k fl o\\'. , 'co pagt• IOfi. 

. 11 :3. Lithoidal h yper ·t.hcne- lacite, \\'a ter's cd)! , head of lr t worid Co\'C. , , page 11 3. 

141 

r o. J J-l. • 'trea ked , ,·itro phy ri · hypersth ne-dacite, near \Vineglas., (~ rot o <l\'(' on th ea~t. id l' 

of the lak •. ee page 114. 

:\o. 130. lly pe r thone-dacit , lithoidal typ , from a ~mall dik t hat ut ~ the older fl o\\',' inltllediatcly IJ IO\\' Llao Ro('k . 

. J.J: .. \ dark-('olo red ~ee ti n foutHl among the da ·iti!' 'i damt>n la. See pagl' 1:10. 

'o. 15 1. .\ lig h t-l'olorod ~cc et n foun d !uuong th <• dadti , ejcetamcnta. S c· pa.g • 1:-m. 

A,; will b cen by eon ·ulting the m~tp tb ba s of 'mte r Lake contpri · , un ix 

the late r \'Oit:ani · er uptiv ma · e tb~tt form the variou , co ne:, mound:, n,ml fhLit r 

lava ·b to the north, we t, a nd south f the lak . :o ba ·alts whatever nr fou nd 

in tbe wall · of tho cra ter or in tbe dike · cutting them. Nor ar they to b :e n on 

tb immediate out-r :;lop of the c rater. 

[n th g r eat majority of <:a ' e: th' I rL ·alts bear a Y ry t lo · r e · mblanc to nwn.r 

of tbe ande ·it , and ·ometime can not surely be d i ·tiug·u i:;hcd a: ba 'ftlt.·. In not 1t 

few case.· , bow 'ver, typically d vclop d ba ·altic :;tructure.· ar to h not d. Tbi" 

typ will be ·on ider d fir. t. 

INTERSTITIAL BASALTS. 

Thi.· typ of ba alt i- r presented h. four . p cimcn · (15:3, l53, 1 ~ -±, l5;:5) tak ' 11 

from the hilI thn.t ris · 00 to 000 f et abov tb J vel of tb ' plai 11 of Diamond Lake. 

i n It extr tu c northw t corn r of th 'mter Lake ~Lrca· al ·o by two speciut m; 

f ront tb !ant tl ow at the ()}'t't l a e of Red n , abo u H mile· north we t of Llao 

H.oc:k on tb l'ntt r rim (156. 157) · a lso by four pecimens tn,ken front d iff rent place. 

j n the hasaltie tll' fl. w ot f Anna ' r k j n the ·xtr me . uthwcst r n corn e r of the 

region mapp I (15 ', 15\:l, 160, l61). 

The r ·ks are all rathe r Light ·olor'd. f a <rmyi::d1 to brownish tio t, ~t d 

<:O tt"tktin occa:,;i nally a f w <'~wit e ·, b n ar nc,·er t' ally scoria eou:,;. The oTains 

ar r nmrlmhly uniforlll and a r rath r d nse. but not ex trem ly so. nder the lens 

th y ~t pp ar holol'rystfllline wd di»elo · oc ·a.·ionu.ll.r oT eni: h to r eddi b oli vine 

g mins and like' i.· g re ni ·h grains of hyp rst.hene. B th oli vine ltnd byp r ·th n 

bav' a d i,..LitH' 1_,. r esinou,:; lu,.;te r. 

A n ab ·olut ly holocry:;talliu ' stru ·turc ca n only Ocl'a:iona lly be ntadc out under 

th llliCI'O::iCOp (15(.) 1 2) but in a ll C:L'eS ll ght •::; bR:-i' p lay,; tl \'Cl'.)' 'UUOrdinatt' roJc. 

The ,.;tructun' i" dominat l by the f eldspnrs, whi('b o · ·ut· in mo -tly ,. r:r distinct lathshrq 0d t'ornt,... \\·hi lt th ' aug ite is ln rgc ly <'011fi11 ed to the ntorC' or IC',.;s ang nl:u· >:~ pa c" 

lwtw ' UJ ti ll' l'dd:par laths. n.ftl' l' tlw lllHntH' l' o r a lllt'::iO:Sta,.;i,.;. Thi,.; strudun· IIIH\' he 
l'ETJWGHAl'H Y OJ!' ItATEH LAK I•; N 'l'lONAL l'ARK. 

tL'rrned inte rstitia l (H.o:scnbu:-;ch's ·' inte r::; rta.l st ruk tnr ''). T he ro h in qu :-; ti on, 

howe' e r, a r too d ided ly f ld ·pathi · to o·i,, • typica.lly in r. titial struC'tur 's. In one 

o r two ca · ::; they ns.· urne <L nearly hypidiomorphic (1 G) and in oth rs a po rphy riti · 

st ructure' . The po rphy ri t i · dCI'L' Iopmcnt, however i.· cau. d hy th o · ' Ul'l' n ·' of 

phC' nol'ry::>t'.l of oli vine and hypcr:thenc, a.nd mre ly ol' :wg ite or pla.g io ·Ia ·c. 

;\1D1B LUL CJOML'ONENT '. 

F.EJ.D,' PJ\ H. 

Tb fe ldspar is entire ly phLg iodase, wllil'h , on rweo unt of it::; g r at ahu nda nL"C'. 

dolllinu.t<'s th st.ruc:turc of th e roC'k. 1t has th ' mth r lo ng lath fol'lll t'Oit1111 0 n to 

l.m:alts of this e la ·:-; . In most eases tb lath: <L I' rather irreg ular in outlin ', hut 

ll'hcn' ag-las: ha>l' i:; morl' in cvid n c. a:; if' uswtl l.)' t h ca ·', the edge of t.he · la tl1 

fo rms rnay b quite s ha rp. In : u ·b ca,.,e · th nd. <tr cutoff quar ly. a::; though 

hy a pi 1mcoidal faec. \ VherC'ver t h fl.b en · of n. g la ·::; IJase pre1·entr· h :f r 'd v •1-

oprnent of the terminal h ·e be long : id ,.; of th lfl.th · ar mor e p rf ctly fo rm d 

than ar the e nd.·. Their I ngth :-~ u •uall.v · veml tim : th ir width. The g n ral 

.'.l bapc of these p lagio ht-· ·ry:tal.' is tabu lar, a: t he square ·r ss ·e ti o n::; ·o ·bam ·-

teri: tie of plagiocla:e in mi ro li t ic form ar c ·o n: pi uoLvl.Y ab" nt. The d iffe r nt 

th in scet ~ of t h . e basa lts pr · nt not a. li ttl Yari cty in the siz:e ;tnd unifonnity 

of t he f'ld:-;par,.; in the .s;uuc : pecinll'lt. u. lUL wi ll Hl'l'V<' to i llu,.;tm tc o rH' in 

whi eh t it fo ~ pur:; U I 'O Lllllii.:! UU.lly Ull iforrt t in :;iz:e . Tln; ir <LI'l' l'Hg'' I •ng tlt i:-; u.~ millillll'tcr . No . . 1 ~~ and 157 ~; ow mu h g r a. r n tria tio n in th<' : ize of the fc ld: 1 a r;.;, 

t!Jos' of No. 157 ha1·in o· an avcrag length of ~ millimeter. with a nmxinutrn of 

0.7 mi llirnet r and <L minimum of 0.1 millimete r: th fe lcl -pa r · of o. t5, ha1·c an 

a1·erage of 0.1:3 millim ter with.a maximum f ~ millim tcr Lnd a n?inimurn of 0.0-1: 

rnillirn et r. Mo:-;t of tb p lagiucla: hLth · d i dose ·ba rply defin d I o lysy nthc ti c 

tw inni1w, th , 111all e r ancl lliOl' : 1 ndcr lath: ba,·i1w two or th r e a nd the la rg r one 

ha lf a do>~ ~ or mo r s ripe . In Nt·h thin sC' tion , how v r, tber a r not :t f ew 

incli du~d th t do not appear to h twinned. Tbe r i: no good r a. on to inf r tbat 

an y of t h 'se rcpr' ·enta mo nocli11i c f•lclspar. ·ua lly uch u utw inn d indi vidual: 

hu1·e IIlli ·h broad r form:-~ , : n ·h a: one w uld xpP. ·t to ·c in fL tabu lar plrtg ioda:' 

eu t p:ml.ll c l tu the lar"·cst face. Th ' : u ppo:itio11 t hat th i::; is the ca:-;c i: str ' ngthc ncd 

IJ,\' th' frequent a1 peanuw of we ll-defitwcl clea1·agc cradiT tbat corre::;pond in dire·-

tion to th basa l d eaNagc of plag iocla:-;c. The · Jarg r appare ntly untwinn d ·ectio u · not infrequ<'ntly <tlso s how a well-dctined r-onal . tructurc. whit:h . tructur e may 

al. ·o IH' ;.;e(' n <l.t tinws o n tlw btrg r ·rystal g rain: t hat arc C' Ut HO as to how the 

twinnirw. : is g0 1lL' m lly t h case in 7.0nal plagioc· lu ·es th(' r-o na l h<Lncling- i: best 

s~ ll n th hnt ·bypioacoid. Th 'XtLn ·tio n :tng lcs ob. en rcd indicate a \'Cry basic. 
RA ' AL1\'. 14:3 

plagioclu ·c. JmnJ cly. anorthite. Mca.·urements mad ou ,.;c(·tion · at right :tll g"lcs to 

tb bm ·hypin:tcoid- that i.· on .'ections thrtt give qual cxtincti n <llwles to th rig b 

and to th e left of th e trace of the twinning plan ga\'C maximum angles \':trying 

between 30° and 30° (the Ia t-nam d ;tngl wa>; ob:erv d in No. :J~). Th se tucasurcmcnts were made on cry ·t:ctls of differ nt siz ':, not onlr on t h hu'U'est on •,.;. In ,) ,., ca:>cs wh rc t.h c in diviJuals were too slllall to allow on to det mtin the direction of 

cutti ng the ,·cry brg extinction ungl s commonly obtrLin d al:o point to n ,. ' IT 

ba ·ic feldspar. 

\Vitb tb • ex<.: ption of an occa.·ional apatit' 11 di e and a littl • blark dust th .-;e 

fclcl pars arc fr from inclosures. \.n exception to thi · stat m •nt mny, pcrh~Lps, 

h taken in that where the du t i:; ·on:;pit·uous th er e is not unlikely also a snmll 

amount of gla: · in closing it. Part of this bht<.:k dns app <Lrs to IJc upaqtll' and lllay 

be con:;id r d to be magn tite, but uth •r p;Lrtidc ·, wh 11 higltly ntag nifi ctl, lose their 

a1 par nt opacity as w ll as th ir blaekness. Tbcs la.t arc undoubtedly glolnditic 

matte r. :-lu ·b dust-laden glas. i: quite similar to the ·tnall nmount of glass base that 

at tim : ntay unmi ·taknbly bed tcctcd I etwe n tb phwiocla lath · of thc:c and of 

othe r basalts of tbi: region. ln a f w ca. cs (L5") n , mall number of s mcwhat large r 

and tbi ker plao·iocla ·e rystals an• to l n thnt may ]JOS i LJiy he <· nsiurJ'c•d as 

ph no<; rysts a.nd a. hclong·ing to an older g neration. hut th ey hear li ttlr r sP nthlanct• 

to the more chara<.:t ri:lti c ph nony:ts of the nndc::: i i0 hasalts d •scrille<i furth ·ron 

in the ·e pag ' . 

.AllO I'l'E. 

Aug:ite is }Lbundunt, but i:; in varial>ly much los: ::;o than plagio ·lase. It appear:; 

in thin ·ection in pal -g reeni ·h or y llawish-grc n color:l. and nearly alway · in :mall 

a twui}Lr gmi n · Iilli ng the I aces b tw' n the fc ld 'P<LI' lath.'. Occa ' ional exceptions 

to thi:; rul tnay he 111 nti ned (1."3) wh rc th ;uwitc a;-: umcs in part roughl y pri:lmati form. r mbling tha of th hypC'rsth nc ·. It i. inntriably you ng r than t.h 

plau·locl<lSC' and also younger than the hypcr:;tb ne. Jn a :f \\' ·a. e · (l"()- 1."7) ·ontirruou · or adjac >nt g rain .• ha\ c ·imultan ous xtinetion, and de,·elop into an ophiti e 

stru ·tun' thro11g·h l artially inclo ·eel plau·iodase laths. Auo·ite is usually ntu ·h more 

abuntlant than h. pcrsthcno, althoug h it may IJe ·ont ' less ,.;o (152). \.: a ge neral 

thing th • augit i.· p •rfc ·tly fre:b, but hrowni: b to deep-red iron oxide :.:taim; an' 

'Oillll!Oil. 

II Y 1'1-:Hl;TII es ; 

Hyp rsth nc is a ·bamdcri -tic but not a lway: abundant con tituent of th :; ' 

bft. a lt.-. lt is ,. ry tlnctunting in amount. AltbouJ·b it may be more ahundnnt than 

:LUo·ite, as ahovr noted (15.</), it i · gc n rally not ·o ahuntlanl,ly r pn·scntcd. and in OtH' 

ca · apt ar::; to lw ntir I r nb:.: nt (161). ft occur · aln10st inntriably in sntall. fairly 
PKl'lWGHAl'HY 01'' CHAT:Elt J,A K:E A'l'lONAL PAl{,K, 

w 11 -de.lin d pri::;m ~; tuat arc two or thr time.' as long a: wide. ln th ' 111 orc di::;-

tinctly bolo ·ry tallin e yari cti cl:i tbi: min ral i,; :dmo:t g mnular, th pri: mati c habit 

b ing ,, ry r oug hly d \·c lop d. On tb oth r hand . whcr th ·tructurc is l ·:cry:-

ta.l lin cand th cgla:: ba::;c di ·tin tly r ccoo·ni2abl , th e ·bara t ri.-tic habit of hypN:-;lhcnc 

can readily b mad out. In such ca · ::; tb form · ar brn, hypinaco id and m:t ·ropinacoicl with :-.; ubo rdinate pri: n1 terminated hy lt tl:tt pyramid. ln o lor and pl cu-

·h roi:-.; nl th y t'xactly rc ·emhl ' the hyp r:-.;th ncs f th andc:itc,;. ln the very tl1in 

:-.;cction ·, howc,·cr neccl:lsary for the -tudy of the · ratlPr fin -g rain d rock ·, it i.- not 

easy <dway;, to d i. ting ui h b tween augite and hyp r: th nc. Jn ;;u ·h ca.- :, t.hc gc nral fo rm, pa.rall c l xtinction and low r dou blc rcfnwtion arc u ·ually su fii cicn t. In 

th fin r g rained pecimen;, th e hyp r:th n do s not dift' r u rcatl from th' plag iolasc lath · in ::; iz , b ing p erhap.·, on th av mg , ·om ' hat ·muller; in th coar: r 

r ·k: th y fH' <tpt to be decidedly . nudl r than th fc ld: par lath ·. They a.re n a rl y 

f ree f rom in lo ·ur , magn etite octah dr n and an oc·cfvional apatite pri. 111 b in o· 

th on.ly ob:;etTcd xception.-. As ta.t d above, th y arc older than the augite 

g r a.in::;, }tnd :cem al ' O in mo:t cases to he old r than th phwio la . 

Parallelism of gro,-vth b tween augit a nd hyp r th n i a con1mon oc ·urrcnc·c . 

Thi i: mor noticeahl in tb ba ~· alt: that ar l oo r in aug ite. In su('h parallel 

g rowth · th augite invariahly a1 p an; a:; a : I nder strip o n acb : ide of a pri: matic 

bypcr.tben pri m tb two trip::; on the oppo: it ide o f tbe cry 'l:aJ xting ui: bing 

togeth er. V cry rar ly may aug-ite be .-ccn on th e end of a hype rsth ene l' ry .-tal. lt 

i: worthy of note that tbi · paralleli ·m of g rowth l etw n the · two py roxc n ::; i. not 

un i v r::;al, that i ·, not a ll of the hy per ·tbcne:-.; in a ny one thin · ction are tbu: horde r ed 

by aug ite. 

O LI\' JNE. 

Oli\'inc i.' a con ·tant but Yc ry fin ·tuating ingr ' di nt. lt appear,; to be parti cularly abundant in tho c rock · wh r ' hyp r ·tben , . itb r mi: ·ing or at lc:t:-.; t 

not abundant. No. 157 well illu trat · tbi · fact. Tt i a nearly bolo ry. tal line 

ba ·alt, with abundant augite and olivin , but with only two o r three b.n r: tb ne 

individual Yi ible in a thin .-e ·tion. 1'h olivin appea t· · itbe r olorl ·s or slightly 

y ellow but it i::; f requent! ' ,;l:.c'l.ined blood r ·d along tbe inegnla r clea,·au era ·k!:J. 

In a f w ca ·e · a slight .Jcrpentinization ha,· start·d in. The oli vi n o ·cur: u;,uall y 

in g ra.nular form or in cluster. of oTaiu:; and only ex· •ptionall.) in roug hl y d fin ed 

·ry:tals. It i: the large ·t con titu nt of the ·e basalt · a nd is the only on ' that lllay 

be cia 'H d a: a ph noc ry.t. ln No. L52 th e oli vin appea r: to ha,·e. ufi'e red to some 

extent from nuto·n.a.ti c rc o rption . Thi:-.; i: indi cated hy ~l border of opaqu ore 

g ra in ·. This black border docs not occ·ur o n all indi1·idurtk ft i. be:t s en on th 

small r one:. Jt may oucur on one nd of a cry ·tal fmd he mis: ing on th e other 
BA ALT . l45 

end. few of the mailer cry tal . bow only a cor e of unalt r d oli,Tine wbil tb 

greater pa rt of the ryst.:'tl ha been tbu. aitered. In tbi · pe im n th m:tll 

individuals of oli vine are unu ually well defined and bow quite di. ti nctl} tb crystal 

hape. In uch ca ' e · the g ranular rna of or ba r et.'tin ed tb ri ·ina[ cry ·tal form 

of the olivine. The olivines . bow occa ional inclo ure. of magn tit :10ci a] ·o ou 

in a while of brown g la :. 

MAG!'iE'rJTE. 

Magnetit is not pre nt, in yery great abundance. It oc ur. in tb u tomary 

grain and small octahedral cry tal catter d throughout tb ro k a.nd inclo · d in 

all the other ino-redient!. It vari con iderably both in amount and in tb ize of 

the ind iYidual cry ·tal , but it oev r as ume t he imp r tanc that i. ordinarily 

expected in ba a l . It a l o occurs, a. de cribed below, in the form of fine du t 

impr eo-nating the inter -titial g la . 

A a lr ady m ntioned tb g la. · base of th e ba a lts varie . om what in amount. 

It is ne,·er ve ry co o ·picuou,, and it vani-he. almo t entirely at tim . . In a numh r 

of a e the o·la can not actually be seen but it · pr n c is probably indimtted 

by the occurrence of black du t, wh ich i · probabl. m~t etitc <Lnd globuli tic matt r , 

and which o ur eithe r in ·eparate but Y ry minute g-rain · that are too .·mall to 

mea ·ur or in very mi nute r od-lik or ricbitic-lik g rowths. ApJ ar ntly tb e"e 

opaqu particle· ar inclo ed in the feld par , but a tb yare to b ecn mo tly at 

the junction of the plagiocla e lath it i more like ly that the are reall.\7 mb deled 

in a v ry thin fi lm of g la . None of the pe imen above de rib d i ntirely 

fr from tbi~ bla k powder. 

Thi · inter titial .. tru tur i b rought out in fig. 0 of P l. XIX (p. 13 ). 

Th ch mica ! analy. i of No. l5 will b found with th e analy e of other 

ba ·a l from ' rater Lak n pao·e 161. Altbouo·h his i a typical an example 

of ba ·alt a · may l c found a.r und Crater Lak , th e analy is indicate a r k 

lo ly allied to tb and ·ite ·. It i eli tinctly mor a id than i the olivine-b a.ring 

ba u~t (173) a de~ ription of wh ieh may be found on page 155. 

A partial ttnaly i of another in terotitial ba alt (16..,) " ·as anied out in the 

chcmi a l laboratory of t he oloraclo tat hool of 'Mine by Prof. H.. N. Hartman. 

Thi · a nalyRi · o·a,·c i0 5~ .1 p0r cent. It' ould cern therefore, fr om the ' two 

analy ·c · that th int r ·titial ba. alts of 'rater L ak ha\' uou ·ually high per entages 

of : ilicu. 

HYPERSTHENE APATI'rE AND P EUDOBROOKITE RY TAL 1 . BA ALT. 

In a pecim n of ba alt of tbi:; typ collect d on tb ea t ba e of H. d Cone 

(156) occur numerou :fl atti h c.wities that measure from on -quarter to no-half 

\1255- No. 3- 02-10 
146 PETROGRAPHY 01!' OR TER LAKE ATI N.AL P.L\RK. 

inch in g-reate t diam ter. The. 

different kind,; fir t, b) per thene; 

unknown white mineral. 

caviti arc lined with minut cr l:<tl of four 

econd, pseudobrookit ; third, apatite; fourth, 

The cry tal: of byp rsth ne occur in very brilliant though minut tablets, 

tran parent, and of n, fin deep-brown color. \Vh n examined und r the mi ·ro-

. cope the ·e cry tal · giv the properti of hyper ·th nc a, ccn in e ion pnmll I 

to the brachypinacoid. Pleochroism i mn.rked with gre ni ·h e lor in the dir tion 

of the v rtical axis and a decided brown at right angl · to thi::; direction. The 

extinction i parall 1 and the vertical axi the dire ·tion of 1 a t la ticity. o 

optical image an be obtain d on th la rg cr) stn.l face. 

Owing to th extreme brillianc.r of th e hypet" thenc ry tal and to the fa t 

that they appeared to pre nt intere ting cr} tal form , pie c · of the rock ·onta ining 

these cavitie w re ent to Dr. C. Palach , of Harvard niver ity, for further !dentifica.tion and mea ur ment. The writer i xtremely indebted to Dr. Paiftchc 

for working out the form · of the e cry tal a well a for the identifi ation and 

mea urem nt of tb p eudobrookite cry -tal . The r ult of t.hi pain taking work 

i given below. A will be ·een by omparing hi mea ur m nt the uppo. ition 

that the e brown pleo hroic tabl t ar hyp r tbene is abundantly prov d. 

The cavitie, al o co ntain a very few bla k and not well-defin d cry tal whi ·h, 

under the micro ·cope, appear to have a deep r eddi h-brown ·olor and to how 

no pleochroi m. Althouo·h the writer i.· not certain that th · bla ·k •ry •ta,l::; ar 

the ·arne a. tho c identified by Dr. Pala ·h a::; p eudobrookit the probability is 

in favor of that uppo ition. 

APATITE CRYSTA . . 

Apatite occut:s 111 very delicat , minute, . I nder n edle . Th identification 

a · apatite r tl upon the needle form 3-nd th fact that they po e · very low 

double refraction and have parallel xtinction with n gative xten ·ion. 

The unknown white cry tal oc ·ur in abundant, roundi ·b form which, wh n 

broken are ·een to b . ao-gregate ·. It i po · ·ible that they arc tridymit with 

which th y have . orne re emblance, but thi ·ould not be prov d. 

Below i ubmitted the report on hyper ·thcnc ~LOd pseudo brookite cry ·tals by 

Dr. C. Palache. 

IJYPERSTIJEN E RYSTALS. a 

The hyper th n i in th form of minute tabular cry. tal: , 0.:- to 0.75 millim t r 

in I ngth , 0. to 0.5 millimet r in br ·adth, and about O.l millim ter in thi knc s. 

They are.alway atta ·h d to the wall::; of the cavity by an edge in tlU h marin r that 

double termination::; never occur. Th face are bright and .,;parkling xcept 

- --------- II 'J'h(; clc . ·ription here given is th" work or Dr. c. Pnlacbe. 
BA ALT . 147 

a 100 which i sometime triated parallel to the vertical dir ction- but on nccoun 

of their minute . ize th e r etl ction are dim, and the r ad ing , th r fore, ' ubj ct to 

con id r able variation . . 

The ob erved form · (po ition of G roth , a: b: c= 1.030 : 1 : .5 ~) wer ns 

fo ll ow : 

a, 100 

b, 010 

tl, 210 

1U, 310 

m, 110 k, 102 

i, 121 

u, 322 

The mo. t f requent ·ombina.tion of th e form i.· how-n in fig . 1 of Pl. XI 

(p. 76), which i · <tn exact reproduction of th figur o·iv n by hmidt " fo r th 

hyp ersthene from Ma lna Hungary .o 

k, 102 also found on th · Malna cry. t..'tl. wa, found on! on R sitw l cry t.'tl 

bown in fig. J of Pl. XIV , Lnd the . am 'va,· true of 11, 21 rL . ing l mttT w fa e no 

bown in tb drawincr. W : 310 wa ob rv d on :;everal ry tal · and rn a ·ur d on 

two. Tbi form wa first b.~ rv d by Fouque on hyper tb n from rtntorin ,c but 

h d id not indicate it a.· new and o·ave no measu rem n . It hrt tberef r been 

r ejected in mo t of t he recent li of hyper tbene form , but appear · to hav b n 

confirme l by th e present mea ur ment . 

Mea ur d. 

p 

0 0 

111, 110 .... oooooooo ----- ------- ---- --- ---- --- 4! 12 90 00 

n, 210 0 0. 0 0 0 .• 0 0 0 0. 0 0. 0 0 0 0. 0 00 00 0 0 0 ooo 0 0 . . 0 0 62 46 90 00 

tn, 310 .0 0. 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 oo 0 0 0 0 00 0 0 0 0 0 71 ~ 90 00 

k ' 102 oo oooo oo•ooooooo oo oooooooo oooooo 0 --- - 9 00 15 55 

i, 121. 0 . . 0 . . 0 0 0 0 0 0. 0 0 0 0 0 •o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 •• 0 2' ~5 52 3-! 

u, 322 .. 0 .. 55 ~ 

------ 46 06 -- ------------ ---- ---- ---- I 

I'SE J)OIJROOKI'J'E CHY 'l,ALS.rl 

a.lcuJated. 

p 

0 0 

44 07 90 

62 H 90 

71 02 so 

90 00 r 'Y 

- <> 52 52 

55 30 46 

00 

00 

00 

56 

36 

OS 

Num b r 

- of r adings. 

1 

5 

2 

3 

2 

A company ing th hyp r.-thcne in a. ingl ' avity were ·e,o ral . l nd r, ne dJ · 

li ke ry tal · hfLv'ing a hrilliant meta.lli lu ter. Tb ir a1 p araiJf'.P. lLnd the a ·soe iu -

ti n in which tb y occuned r call ed the d 'Cription of pseudobrookit ' a · found in 

th e byp rsthcn -a n de ite of Aran_y r Berg, Hungary- e ftnd, notwith ta,nding the 

minute ::; i;r. e f tb cr. tal ·, jt \\'a found po . ible to obtain approximate mea. ur · 

m nt:; from two of th m, wh ich ecm to c.ontirm thi determination. 

"Zeit. i(ir Kryst., \'ol. ', l ·, p. 210. 

b'.rhis figure is giv 11 by Dnna, p. 319, Og. 2, buL with incorrect lettering. With the >tx es there adopted, the letters 

allnd bon the two plnacoids should be t~r ·bunged. 

o Bull. · c. min . Fmncc, \'ol. J, 1878, p. 47. 

tiThe desc ription he r given i the work of Dr. ·. J>ahlche. 

c Among other, Truube, Zeit. fU r Kry•t.. \'ol. XX, 1 9'l, p. 327. 
14 PETROGRAPHY 0~' CR TER.L KE ATIO L PARK. 

Th form found are ' hown in fig. K of Pl. rrv (p. 76) and in the following 

table, togeth r with th mea nr m nts: 

1- p 

0 0 

a, 100. .. ........ . .... . .. ...... . ............ . 9 00 

b, 010 .. - -... ----._ - - -- ----- -- --- ---- . -- -- . -- . 00 00 

m, 210.... . ..... ............... . ........ ... . 63 -!2 

I, 110 . . __ . _ .... ___ _ . .. _ .. . _ ... .. . . _ ...... _. _ -!6 00 

e, 103 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 00 

90 00 

90 00 

90 00 

90 00 

20 57 

90 00 

00 00 

63 ~ 

-!5 23 

90 00 

0 

90 

90 

90 

0 

20 

rumber 

of r adp ing. 

00 4 

00 4 

00 6 

00 3 

53 2 

The face · of the pinacoid , a and u, w r brio·bt, but th pri ·m::; w r deep ly 

triated and gave very poor r flection . 

The position her e adopted i that orio·inally proi o · d by Koch * and r etain d h 

chmidt, Traube, and Groth. With Dana and Golds ·luuidt th axe· h and t ar 

interchano-ed. Th form r ::;eem the mor natural ·hoi , in vi w of tb ' pr nounccd 

pri mati c habit of the cry tal. a.nd .·inc th e chemical r elation · f [ .·cudobrookite 

to brookit Jo not . eern to bear out h appa.r nt form r lation:; betw en th two 

min raJ. which it wa, the purpo. f th alt r d po.·ition to exr r c · . . 

FL .IDAL-TNTER TlTlAL BASALTS. 

In at lea ·t two in tanc · (152 and 155) tb abo,·c-cle cribed inter titia l ba alt · 

di clo e a decicl c1 tenden y to·warcl a tl.uidal arnwg- m nt of the plng-io ·la c lath · and 

thu · pT ·ent a, tran ition . tag-e betw en the mor typi ·ally de,- loped inte r. titial 

basalt · and what may be termed basalt · with a tluidal-inte r titia l stnt ·tur . Thi · 

Ia t-named typ i · well mu tratccl l y four p cimen ·, three of whi h (162 l63 and 

164:) were coll e t din differ nt par of the ba. altic ar a to the :-outb\ e. t of Crater 

Lake, from which mo t of th inter ·titial ba::;al ·am , and the fourth (165) from 

a widely parat c1 ection, name ly, from the . outhw ::;t slop of Timber 'rat r, 

ituated about 4: mile::; to the northeast of the lake. 

The· rocks con i t of plao-io la e, aug-it , hypersthene, and mag-uetite with 

· almo, t no oli\Tine. Gla. · i::; al o uudoubt dly pr ' ent, but rtainly not in large 

<Lmount. The fluidal ·tructurc is due mainly to th e fact that th plagioclas app ar · 

in v -r y long and ·lender lath form, and to the furtb r fa t that thcs' feld::;par Lath 

have a. ver. marked paralleli m of anang-ement. The tructure ~ indeed q uite uo·­

ge tiv of th fluidally arrano-ed anidin lath::; in tra ·byte · and lllany rhyolite.·. 

Th . e plag-iocl.a e Lath arc quite ·harp in outline or, at least, th i.· may be aid to b 

tru f tb ~id .· of the ·rysta.l;·. They a.r many time.· as long as wide, and have 

* A. Koc h , ~nn . Mltth., Vol. l ,l 78, pf'. 77 rtni! 341. 
BA .AJ .. T . 149 

an averag . .ize of about 0.1 to 0.2 millim t r . The fluidal tru ture i. furthl'l' 

accentuat d by the fa t that the hyper thene and to a con id ruble xt nt al ·o th 

augit orcur in rather lender pri m , which are likewi· arrang d parallel to th 

fr ld:pan:. Hypersth n i di tin tly the dominating pyrox n , being u ually much 

mor abundant than aug-ite. Ito Ul" only in pri matic fo rm in ry !}tis that mea ur 

usually ahout 0.02 to 0.05 mil limeter in I ngtb, and about one-third that amount in 

width. Occa ionally :omewhat larg- r indi idua ls may b en but, a.· a g neral 

thing, their ize i very uniform. They inclo e ·mall g rain· and o tab dral cry tal. 

of magnetit . The augite i to b een both in g-rain and in min ut pri m· almo t 

icl e1 ti cal in iz and appearance with the hyp I" th ne pri. ms. In fact, in whi te light 

it i. almo t impo . .-ibl to di tinguiub between the wo, a. in co lor ·iz hap , and 

in lo ure.· they re emblr acb oth r. Even the pleocbroi m can hardly be u d a 

a means fo r el i tingui hif)g the two py roxene , b cause of th ne e. ' aril,) thin e -

tion · required for the proper tudy of uch fine-grain d basal ' . In po lari z d ]i O" ht, 

however, the di tinction is not difficult. Para.lleli m of g rowth b tween hyper th n 

and augite ma.v be ob erved xactly a in the above-de ri bed rocks the n.u()'it 

appearing in the thin . ction a. ·lender parallel trip on ach . id of the 

h p r th n . 

1h fiuiclal ·inter titial tructme i ·hown in :fig. D of P l. XIX (p. 13 ). 

The almo. t omplete absenc of olivine in the ba a]ts in which hyper th ne i 

unu uall abundant i a further orroboration of the fr quentl noticed fact that 

th de\' lopm nt of olivin in a ba alt is not o much dependent on the chemical 

compo ition a upon th condition of olidification . Ine pective of the fact that th 

amount of oli,-ine in the e and in the more typically developed inter titial ba alts 

appear to vary inv y with the developm nt of hyper thene, it may be remarked 

that the . mall amount of olivin pre ent in all thee ba a.lts fall in lin e with the 

r mark of Profe · or Ro enbu ch,a to the effect that olivin e o cut· most parin()'ly in 

the ba alts of a hypidiomorphic or of a doleritic type. The ba alts under di cus ion, 

althouo·h hardly to b ·alled typicall.v doleritic a r at lea t more allied to that· type 

than to any oth r. 

In ro. 163 are to be ·ee11 minute rod-like microlites of a deep reddi h-brown 

color and almo ·t opaqu . In : ize the}' mea ure on the average 0.01 mil limet r 1 ng 

and 0.001 millim ter wide. They re embl rutile, but do not give the brilliant 

polarization ·olon; chant teri ti · of . uch minute c ry tals of that mineral. In fact, 

it could not be. bown that tb y aft' cted polarized light at all. Th y ha" e not been 

noti ed in th other ba alts. 

The 0 fluidal-inter titial bru alts, when compar ed to tho e already described in the. e 

page a· inter titial, a r closely alli d to those occurring in th northwe t corner of 
150 PETROGRAPHY OF RATER LAKE NATIONAL PARK. 

the Crater Lake area, and more c peciall to o . 152 and 155. o. 164: bow tb 

fluidal tructure much l p rfe ·tly de lop d than do the oth r hr and mn.y b 

con idered a in term diate b tw en the two typ . o. 166 wa, c H t d at th ·arne 

place a ro. 164 and i pl'Obably a locall cliff r ntiat d vari ty. It uld hnrdly b 

lassed here if taken by it elf. Th plagio lase i mu b l ' ftbundant and o cur in 

omewhat larger lender lath , that lie in all dir ction but a re not abundant nougb 

to interfer e with each oth r to an r gr at xt nt. Th bulk of th ro ·k c n. i t of a 

feld.' pathic paste thickly roweled with xtremely minute pyrox n - pri:>m. ~t nd with 

o tahedral cry tals of magnetite. Both auo·ite and hyp rsth ne ar e r pr ntccl but 

it i. impo ible to d terrnin in what propo rtion. 

The e two type · of ba ·alt nr , then, v r.v clo' ely linked togetb r and th 

tran ition betw n the diff r nt . pecim n colle t d a,r mu h clo. r than arc th 

tran ·ition · between thes and the porphy riti ba alt · whos de cription follow and 

till more plainly is tbi trne a compar d with th ba ·altic-looki ng and it · of tbi. 

arne region. The force of thi tatement wi ll b tter be appre iatcd in on n ction 

with the comparison made below with the . o-called hyp r then -and it from 

Franklin Hill Pluma County, Cal. We have e n that many of th ba •alt and 

and tc of Crater Lake can with difficulty b di tino·ui h d fr m ach other but 

thi · can not be aid of the above-describ d int r titial find fluidal-intet" titinl ba alt<s . 

The more mark d characteri ·tics of the e rock for purpo e of ompari ·on wi ·· h th 

ande ite i the almo t complete ab en e of porph, ritic d v lopment. Thi i s n 

both in the canty development of ph nocry ts and in the lack of a younger 

gen ration of the mineral ingredient . 

The ·e fluidal-inter titial basalts (e p cially o. 162) bear a clo r mblanc 

to a rock from F ranklin Hill, Pluma ounty, al. , whi h i · briefly m ntion d 

by Mr. H. 1\ . Turn r in the Bidwell Bar folio.« In hi artie} on Th Ao· and 

u ·ce ion of the l g neou Rock of the ierra Nevada 6 h all it a hy per-theneandoe ·ite, and de cribe it a follow : 

" In the area of the Downievill e and Bidwell Bar atla . bee ar nuru rou 

bodie of a den fin ·grained gray lava, which usually weathers with a laty fractur 

the apparent cleavage being often vertical. The rock i · compo ed of plagiocla ' , 

augite, a . lightly pleochroic rhom hie py roxen , and grain of magn tite. 1he 

f ld. par, auo-ite, and rhombic pyroxene are in the form of minute elongated pri m. 

or lath , and thi is true of ·the rock at widely eparated localitie , and the lath of 

all are n arly of the arne ize. About half a gram of ro. 661, powdered !'tnd treated 

with HCI by George teiger, yielded no gelatinou. . ilica, but nev rthele. . there 

appear to be orne gla-. present. " 

Through the kindnes of Mr. Diller the writer was enabl d to make a 

tudy of a thin ection of No. 661, referred to above. The re mblance oetween 

b Jour. Geol. , Vol. III, 1 95, p. 409. 
BA ALT. 151 

tb e rock whi h Turu r call a hyp r then -ande ite nnd tho ju t de crib d from 

rat r L ak i · e\·en clo' er than might be inferred from the abov -quoted de ription. 

Th differ n ·e at· m th r in the iz of th oTain than in mor importn.nt matter.'. 

On , e the am deli cate, uniform pri m: of rhombi c p rox n nnd of augite, 

the am lender feld par lath , and. locully d ,- loped, in the thin . tion the am 

parall li m of ·tru tur . In the California rock the pyrox ne ar ·omewhat laro· r 

and th r efore mor e plainly d lop d. J\!Ir. Turner al o g i.\ :::; in th ·ame pfl.p r a 

parti:tl chemi a! analysi , a · follow : 

Pw·tial chemical analysU! of hypersthene-cmdesite jrom F'l·anklin Hill, Plumas ounty, Cal. 

661. , . N . 

•. -- ... - ... . -.- . . ..... . ..... . .... .. .. -... --- .. -- . . . .. --. . .. -.. i\6. 90 

aO . ..... . .... . --· · -- -·-·· .. . ..... ...... . ... · ·- -- · ... .. .. . .. . . .. i. 3 

K 20 .. _ .... . . .... _ .. _ .... .. _ .... _ ...... .. .. _____ ........ __ _ __ __ __ 1. ~ 

N a.O . . . . ____ . ___ .... .. ... -.. ....... . __ __ __ . __ ....... .. ___ . __ __ __ :3. ~ 

Thi analy i alone certainly eem to ju tify Mr. Turner in culling- th ro k 

h de cribe. :tn ande ite, but upon clo inspection it will b e n that the ana l~ i 

r eally that of a rock intermediat between a ba: alt and fUl and it . · far a 

th iii a alone i concerned the amount i more ugge tive of a hyper then -and ite 

than of a ba. alt. But the per ntag is only a littl ov r 1 high r than that o-iv n 

fo r a ba alt <Yla (ta hylite) from li ebi.ihl, n ar Dran' feld , Hanover. a l< urthermore, 

Mr. Dille r ha: publi ·h c1 a li t of ch mi al analy. e of qtrartz-basal fl'Om Cinder 

'on , northea of La · n P eak, ':tlifornia, 0 in which silica rnn a high or high rio one ca' e thr -quart t" of 1 I r cent hirrber- than that giv n fo r th e Franklin 

Hill ande ii'A' . Inasmu h n Mr. Iddino· ha fairly d mon trat d e that the presence 

of primary quartz in ba nit i: not du to tho xce i\ e amount of ilicu pre ent 

m t h magma, it may w ll b laim d that th rock from Franklin Hill iR not 

o sari ly to a i<l for a ba alt. 

Wb n tb lime. pota 'h, and oda in tbi rock ar ta.ken into a count it would 

b , 1mpo · ible t di ting ui b a to whether the ro k were a ba alt or an aude ite 

fo • it would be a 'Y to cite analy e of both rock · in which the e ub_ tauce are 

pre cnt in almo:t tb xa t r elation hip that are o·iven in th e a · under di cus-

• 1 n. As t wh tb r th Franklin Hill rock hould r eally be called a hypersthenebn a lt in tead of an hyp r tbcne-and ·ite t.h writer will not a ume to ay, a:; 

th1 mi o-ht well dep nd on urrounding a ociation with which he i not , uffici In th ab enc of a hemical analy i of the finidal-inter. titia.l 

. . Geol. u n •cy · o. 79, 1 91, p. 29 . 

• p. 220. 
152 PETROGRAPHY F CRATER LAKE ATIONAL PARK. 

basalt of rater Lal it may perhap · b a · um d that the com1 o ition doc not 

vary gr atly fron.1 hat of th ''a liforni:t ro ·k. bv n . o, n ac ount of the lo ·e 

r emblan to w 11 -cl fined bn altic yp . of th ame regi n and 01 1 nc ount of 

the ·harp contrnst it pr ' nt:- to th · and ites f thi:; amc r o·ion, on ma.y in th 

opinion of the writer, b ju-tifi cl in ai ling thCl c ro ·k ba t ·. In ::tn) ca ·c on 

account of th great vari.tbility in th hemical analy . of ro ·ID:! '" ar ac ·ustom d to ·la · und r th ·ame famil_ nam th e :stru tural r lation hip ' would 

el'\' . bett r a:s a means for d t nnining th ro k nam than \\'Ould th ehcmical 

analy -is alon , ·p ially in ca. e · wh r tha.t anyal.) i. i not t_ypical. 

PORPHYRlTl '-1:'\TER TI'l'lA'L llA 'ALT:;. 

Thi typ ot basalt ma~r b aid to co ntain well-? {:in d and u uall~' abundant 

ph nocrys alway of livine and g n rally al"o f plagio Ia ·e, hyp 1'. thcne, and 

aug ite, in a groundma - that bear a more or le · ·lose r milan c to th int r titial 

basalt. . A · a rule, how ve r th g round rna · i ' inclined to contain mor g la and 

the mineral · of the . econd gen rati n have mor harply d v loped form than i the 

ca e with the corre-ponding min tal - that compo ·e th int r · itial ba alt . 

The Java of De ert Cone, immediately n rth of R d th 

be t xampl of tbi type of .·tm ture. Red Cone al o i 

that belong to this t} pe, but not ntir o, a will appear lat r. 

The la' a of D crt Con i · repres nt d hy thr c spe imens- o. 1G7 from th 

north side n ar th "ummit, and ~os. 16 and 1o9 ol1 cted clo to · th r about l mile 

farther south on th outhern lop . ll tbre are" ry much alike. In the sp im n 

from the north id olivin i the only ph no ry t; in th two from tb outb ru ·loi 

in addition to olivine, plagio e, in a rather -- ubordinate role, occur as a ph nocr ·. t. 

Th olivine in the e . p imen · i. to be " en in ve ry .. harp idiomorphi ry tal 

and al in ·ry. tal fragw nt. . They are parti ularly well adapted to a. tnd of th 

cry talloo-rapbic forms and optical propertie . At fir t glanc orne of the olivine 

ry tal.-, e pecially th frao-rnent~ re mble augite m what, the olor being a light 

yellowi ·b g r en. lrre pecti,,e of the cry tal form bow v r, on ·an u ually di ·tin -

gui h both the cry tal and he fragm nt · by their unu ual1y rough app aring urfa ::tnd by their high interference olor ·, al o by the ab 'en of w 11-d fin d 

cl avage~,; . They u ·ually appear in rectangular or hexagonal ·hape . The dominant 

form are the brachydome (021) and a pri m. In . ction · cut parall el to the ma ropinacoid tbi. combination give · hexagonal outli n , tb angl e formed by tb tra · of 

the brachydome being not far from 0° . ncb a ·ection al o g-ive a po itiv bi ectrix with large optica1 angl (16 ). 

In o. 169 tho oli vin phenocryst have v ry barply develop d form · and show 

an ext n ·ive alteration to iron oxide . Thi · alteration product occur. both a a 
BA ALT . 153 

broad rim and a fin ly granulated rna, e' catter d throughout th cry tal. ln th 

,·cry smalle t r ystal the olivine ha been almo.'t C0!11plctcly repla d · in th ]arg r 

one · the unaltered olivine ra rely compo.'e mor than one-half of th ntir bulk and 

g -n<>rally much 1 : · tbfl.n one-half. Tb i iron oxid alteration product co n i sometim · of p erf ctly bh k opaque material, wbi ·h i · pre umably magnetit ; in other 

<:a e th g rains a re , ligh tly tran. parent and are of a deep r ed co lor, . ugg tive of 

h matite. till mor ommonly both mag-n t it and hematite abound. In 1 ite of 

th harpn e' of the ry 'tal form th e oli' in pbenocry 'ts are fregu ntly p netrated 

by p lagio<; la lath thu indicating a \

7 ery ba ' ic feld par. ( ee fig. L of PI. XIV 

p . 76.) The, p netrating feldspar lath do no occur in the center, but only at th 

marg in of tbe cry:tal · occa ionally al:;o, one ruay e an olivin cry ta l impr ~ in a 

it:> fo rm on a p lagio la e pbenoc ry.t. Thi , however, i by no mean a common 

as the other ca . It would ·eem from· thi that tb f ld par' bad otumenced to 

ry talize out b for tb oli vi ne bad cea ·ed to grow. Po ibl they may hav 

b gun imultaneou ly with tbe olivin e . 

Th only other pbeno ry tin this ba a lt i plagiocla , and even thi i ab ent 

from on e of tb th ree pecimens (167). It i by no mean on pi ·uou. nor ver) 

ma r kedly cliff rent from the mailer feldspathic lath that mak up tb greater part 

of the g roundma ·~ . The shape i r ct'Lng ular or long r e tano·ular. The large. t 

xtinction ano·lc · noticed on ction cut p rp ndi cular to the albiti twinnin o· plan 

wa 30° in No. 16 a nd 29° in o. 169. This doe not indicat o xtr m ly ba i a 

feldspar a it r lation bip · to ol ivin would uo·ge t. Probably if tb plagiocla e 

ph no ·ry. t w r mor nume t·ou 

angle . 

tion could be found bowing larger extinction 

Th aroundma. s app ar · to b nearly bolo r5 talline. It i compo ed of welld \' loped phtgio la lath: of hardly mor than mi croliti prop rtion ·, augite in 

minut gmin or in both pri DP and oTain · and abundant magnetite i n mo -tly \rery 

minute octahedrons and oTain . H ematit powder i nl o abundantly d v lop d in 

th aroundma , of No. 169 • w lJ a in th e olivine pheno ry ·. In add ition to the 1:> 

above-nam d min eral hyper-then ba been r ecogn ized in No. 16 . It i entir lj 

c nfin d to th arouodma and occur, in but on o·eneration. It form · v ry mall 

pri. m that mea ur O.OG millim ter long by 0.01 millimeter wide and that ery 

clo ·ely re. cn1bl imila r pri:>m ofau o·it. They ar too . mallto howa n,Ypleocbroism 

and ar to IJ recog·nized only by their parallel exti nction ' a.nd lower inted er nc 

colors. ln fact, it r equire · ·ome Jittl fami lia rity with th e ro k · before the eli tinction betwe n tb I yr oxcn s can b made. 

In th southwe t orn r of tb a r a cover ed by th_ rater Lake map, a nd about 

ha lf a mil outh of th road, wa collected a tipecimen of ba alt, No. 170, that i · 

losel connected with the inter titia.J ba alt . In a g roundma ompo ed of plagio-
154 PETROGRAPHY OF RATER LAKE ATIO AI .. PARK. 

la e lath , augite, hyp r thenP and ft little du ·t-lad n gla occur p rfe tly dev lop d 

·omparativ ly large plagi cla e phenocr) st1 that xa tly r .~ mbl tb and iti · 

plagiocla. e ; al o an oc a ional byp rsthen , a uo·it , and blo d-r d olivin ry. tal. 

The plao·iocla c i · in broad cry ta ls that h w r ·t..'LnguJar and six- ·id d outlin s and, 

a in th a.nde ites zonal ' tructur . The interi or i rowel d with gla ·s inc! . Ul' s, 

whil e the nMrg·in is fr e from be ame, or el e both tb - interior and tb maro·in a r 

clear whil e h in lo ure::; are confined to a natT w intermcdiHtc zone. n of th · 

pbeoo ry ·t , ut perpendicular to the bra hypina ·oid ga v an ,xtin ·tion an o·l 

of 3±0 . 

Tb groundma ·.· of thi rock, w -rc it f r · e f rom plagiocla ' ph no ry::; t ' would 

be id otical with the interstitial basalt ' . Th p lagiocla ·c lath · at" th dominant 

min ral, and appear to in clo.·e the ano·ular augite grains a w 11 as th littt g la .. · 

pre nt in the int r. tices formed by their in t r eetion. Hyper then , whi ch o ·cur. 

onl) very paringly a a pheno ~-y t i · more abtliJdant in the groundma ", but a it 

i ·found h r e only in pri matic cry tc'li. and not in g rain · like th augite it i prop rly 

not to be con idered as belonging trictly to th groundma .. , but rather to tho older 

generation of crystal . 

Although thi rock pre·· nts an entirely differ nt appearan from th ba alt 

from De. ert Cone. it mu t till be a ign d to th type 'ivhich ha · b en d ignat d a,; 

porphyriti c-interstitial. Jt i · in a wa. in termediate hctw n th hol cry. taWn 

in ter titia l and the ande. iti c ty pe . 

Quite similar to thi. rock i · ro. 171, oil ct d betwee n 'rater P ak a nd un 

Cr ek . 

.. till another development of th porphyritic-inter titial type of ba alt i to be 

. een in part of the Java rock of R d one. The. e arc dark-gray, in on ca. r d 

den , · •ori ac on · lava . The phenocry ·t a re very incon ·picuous, but may h mad 

out under the pock t len . They consi t of yellowi h to r ed oli vine, yellow to bla k 

augite, and white plagiocla e. 

nd r th micro cope the e appear to b decidedly porphyritic ro k with abundant and we11 -d fined, though mall, phe nocry t of olivine, augit and p lagiocla . 

The plag-io lase i the mo t variabl of the phenocry ts, a one p cimen (172, colJe ted about 1 mH outhwe t of th one) contain almo t no ph nocr3 sk f tbi .. 

mineral. Ito ·cur · in rectangular , 1 road to narrow, lath-. hap c1 crystal ·, th e : mal l r 

of whi b rrraduate into the plagiocla of the g roundma ·. The nels of the laths ar 

cut quar ly off, as by a pinacoid, where th g roundma · · i · di tin ctly gJa,. y, but, in 

ca:·e the latter i · mor decidedly cry. talline, the ends are some' bat frayed. They 

in lo eat time · a mall amount of du ty-looking g la . simila r to that of th groundma · ·, but neither in shape nor in the appearance or arrangement of the inclo ure do 

the. e plagiocla phenocrysts r e emble tho e of the andesite or of the la t-de cribed 

ba ·alt. Extinction angle in symmetrically cut sections, i. ·e., in ection perpendic-
BA ALT. 155 

ular to the brachypina oid were mea ur d a follow:-;: 27o, 30o 31 o, a nd 3-:l:o. Tb y 

arc youno·er than both olh·ine and augjt . 

Of the pyroxenes nuo·ite i th only one of on, equen . Of th four . I imen. 

tudied tbre (17±, 175 172) contained no hyper then and one (173) conta ined but 

one individ ua l whi ·h con isted of a roundish oTnin baYing a . mall core of hyp r-

.'then and the outer and la.rger part auo·ite in parallel po ition. Thi g rowth of 

augit app an; to be se ondary and di tinct from tb more u tomary oc un ttc of 

aurrit g r owing around hyper. then cr.v tal.. side from thi on ca · augit o ur:-; 

in gran ular form b ut even o impre e i f rm upon tb plarrio Ia- wber v r it 

com sin ontact. It i to be found hoth i olated rtnd in es~ 1 ith oli1·in . The 

olor i · u ually g re ni b, but in o. 174 many of the grain have a hr wni ' h t, 

or el e they ba,-e oTeeni b enter and . bade into brown on tb ou ·ide. lt mny 

be added that th hand pecimen al o di. clo e:> a f w bla k augite pb nocry. L 

2 to 3 millim ters long, that do not n,ppear in tb thin e tion. 

Olivin i a v ry abu ndant constituent. It o ·cur ' in w 11 -defined om time in 

very harply defin d crystal , a. well a in grain · the latter form b ing mmon 

wber the oli1 in form net· with aurrite and occa ionally with plarrio Ja . In 

o. 174 thi min ral occur xactly a de cribed for No. 169 on f the. p cim n:-; 

co llected on D rt on . It ba t.h e ;·am clear-cut forms and ba und rgone the 

·am alteration to hematite. In thi ·a , bow ,. r th alteration ba prooTe · ·ed 

till f urth r. o onl} hav w the outer rim of almo t opaque b matit but tb 

v ry Jittl clea r olivin vi ibl . (p. 76.) 

Th groundma ' of th rocks i abundant and mo -tly v ry di tin t from th 

ph nocry It on i ' ntially of a ol rl but du -t_,. gla , ba e that i 

crowd d with auo·ite mi rolite. in tbe form of minute pri ms and oTain , al o microliti plagi la e lath nnd harp mag netite octahedrons. The inter titial stru ture 

i n t clearly broug ht out but i pr du d in par . by t~e plagio la of th pbenory.' and in part by tb plagiocla of the groundma th r being· no well-d fin ed 

di ' tinction b t1v en the two. Th' porph_vriti tructure, therefore, ~S much more in 

ev id n e tha.n i.· th in t rstitial. and tbi ~ ro k may b on id r ed in a sen e a int r -

mecliat h tw en the porpbyriti · inter-t itial and the mot· d i tin 'tly 1 orpbyritic 

l>a alt. . Jt do · not ho1> 1·er, bear mu h r e emblance t that typ of porph) riti 

ba al that ar de c ribed a andc::.itie in these page . 

Th h mical analy i of No. 173 will be found on page 161. 

Two pe imen , I o . 17 an<l 177 coli cted about 3 and :l: mile , r spectively , 

w t of Red Cone, ha b n plac d in this g roup of porphyritic inter titial ba ·alt ·, 

although they are decidedly tran itiooal b tween thi g roup and the inter titial 

ba alts prop r. The gteater part of tho rock, as een in thin ection, con titutes a 

ort of holocry t.'tlline g roundma · similar to that of the mo1·e coarsely grained 
156 PETROGRAPHY OF RATER LAKl<~ ATIO AL PARK. 

inter:titinl ba alt . In thi g roundma ' of plagio la · , nugit and mag n tit oe ur 

. orne rather harply defined pbenocry. ts of olivin auo·ite aQ l plao·iocla '· The 

two la t-nam d ph nocry ts occur al o in granul:tr form or in n .'t. f g rain. , and 

g rade off into the n.me min ral · of the gToundma ' ', so that n sharp lin can b 

drawn in eith r ·a between the comr on nt · f the ground11ms. and th ph nocr,r. t ·. In th e a ·e of oli vine, grfl.nu lar form · al ·o oc m· bu the C' ar alway,.; 

di ·tin from the oTotllldmas.' in which no olivin occurs. 

The ol ivine is lightly rp ntinized, a.nd i 'tfl.in d in pla ·c. · a de I r d. It 

·ontain ' inclo ure of roao·netite. The bett r form c1 rrt.'ll ' of augit di · lo 

the cu toroary forms, naro ly, prim two pinacoids, and tlat terminal p) ramidR or 

dome fa e . It i frequently twinned in double, triple, and multir l twin ·. Th 

twinnino· plane is the orthopinacoid. It in lo ' olivin and mag netit , and, to a 

v ry light xtent: al o plao·iocla e. Th plagiocln e cr ·' tals how mor or 1 . 

rectane-ular but not v ry ·harpl) cut, outline·. The p riocl f developm nL almo t 

xactly coin ·ide with thfl.t of the rlllgit a thee two min ral ' oft n impr , · th ir 

form on each oth r. A few rystal contain minut gla s inclo nr bu u ually 

th y are free from inclosure ·, and do not b ar any r mblanc to th plao·io la. e 

phenocry ts of the andesite . 

Hyp r thene app ar to be ntirel wanting. 

ery , imilar basalt, No. 17 , from near thE' road outh of (a. tl 

the Yery edg of the district covered hy b 11_1ap , i ' al ·o pla eel in thiR divi: ion. 

ANDESITIC BASALTS. 

ln n arly all f the basalt. t.hu · far d crib d in the page th , tru tur 

have b n eli tin tly cl iff rent from what ba b en d crib d a · charact ri ti of th 

an de ite ·. To a rtain xtent th i may al o be aiel of th compo ition. But in 

the rocks here d signated a ancle ·itic ba alts the c differenc in . Luctur and 

al ' O in compo ition to a large ext nt eli appear, ·o much o that \-v er it not for 

lo e a ·o .iation with more di tinctly ba alti type om of tho e h r included 

would c rtJ}.inly be cla · ed with th e ancle ite:. In th e ab:en of cbemic.'ll analJ e 

the correctne. of the det rmination. ron t b taken with ome re · lTe. A 

g neral tat m nt of the difference noted betwe n the ande itic ba alts and the 

ande>ite will be giv n at the lo of th mor detailed de cription . c mpnred 

with th for going ha alts, the. e may be, aid to b di tingui heel, ·with one or two 

exception , by the pre n e of a hypocry talline grounclma · or of one with an 

vid nt gla. : ba e, a well as by the pre ence of well-developed pheno ry t of 

plagiocla · . 

Four om what distinct ·tructural types may be recognized. They ar 

d 'ignated a type A, B, c, and D. 
BA ALT. 157 

ANDE ITIO BA ALT , TYPE A. 

Thi ma)· be . tudi ed in three sp ci ~ (179 1 0 1 1) from rat r P ale 

about -~ mi le outh of the lake, and in one . p cim n (1 2) in th cxtr m 

sou~h we -t rn corner of the Crater Lak area. The e arc blacl to blacki,.;h-o-ray , 

,-e ry fin grain d and mostly porou · ro k that have, with the exception of No. 1 .</ , 

8LTiall , hut mth r ·on:picuou Ilagiocla ·e phcnocry ts. Tb groundma. · of the 

ro k on ·i-t of fl l J'Own ish g-la ba ·e douded with black lu:;t and v r) thickly 

·rowel d with I ri matic augite microlite · and with minute maO'netite o ·tab ' lron · "' , and containing microliti crrtal. that on i t of 1·er.v lonO' a,nd . I nd r plagio Ia 

lath . Th lath. ha1·e. traig-ht ;· ide., while th nd ar ometime.· cut quarely 

off, but a,r e mor often ·omewha.t frayed. Th ey inclo. e u ·ually mall amount of 

th du t,r I oking, almo. t opaque, o·la s of the g roundma -: Tb in I ' UrC' ' take 

th e form of minute peck that are -truno· tog ther pamll I to the lono· t axi 

of th lath so as apparently to d ivid the lath in to two or mor lono·itudinal 

ection. . The lath ar not nuw ron.· enou O' h to interlace· to any marked extent. 

The oc urr nc of t;h e lender lath form,' i the 1110 t disti n ti1· f ature of type A. 

The phcnocry. t arc ma,io ly plagiocla. c cry tal. wh ich in No. 1 2 o cu r in 

b road-shap d lath , and a,r imilar to a.ud gTad into the mor . lender and mu h 

·mall er lath · of th g r ur:dma ·, a.nd di clos a.lmo t no in lo. ur . , x pt an 

o ·a i nal bit of brown g la cont.'Lining- cry ta llizatiom; imilar to tho ' f th 

groundma s. The ro k · from Crater P eak, however, cont.'Lin in addition to 

rectang ular or broad lath- hap d individual al o larger and toute r cry t.'Ll that 

exactly n ' ·embl c the old<' r plagiocla. e pbeno r.r · of the typical ande,..itc ·. The e 

u: ually ht11· lear margin and clear ce nter · bu betwee n the two ha1· a narrow 

z nt' that i,; cl uded with browni. h g la:::. indo ·ure ·. om of the larg r ·ry tal 

all'iO ,;how rounded form ' with cmbaym nts du t r c orption , in 1rbich ·a thC' 

el ud d zoo<' follows th co ntour · of th corroded cry tal. being till epa rated 

from th' dge of tb r.r tal by a narrow lear ma rg in. Thi ca;; 1 • xa tly 

id nti c.-'11 with what ha alr adJ b en dcsc ri b d under the and ite ·. 

Auo·i t Clll'. ' a mono· the ph nocry t in mo tly mall and in on picuou · and not 

,. r ' w 11 -d lin d crystal , a,] o in o·min::; a nd i.' not very abundant. Hyp l" thene 

a1 pear to b ntir ly wanting in on thin ction, wh il e in the thor three on!) eight 

indivi d ual.- altog thor \\- r noted. TI1C' ha,bit is pri' matic, but the form is not di -

ti n ·t. ix out f th iO'ht indi,·idua.l::s ha,ve rim E nugite in parallel po it ion. 

Oli vin is fairly abundant in -·mall cr.) stal and gra.i n and o cur. o ·cct 'iona.lJy 

in bett r-f rm d, la,rger crysta l. · of the ordi na.ry typ . In o. 179, how ver and to 

a I ' S xtcnt in . .L 1, th i. mineral al o occur · in fl vcr.r unu ual form. It i i. n 

lono· sl ncl er pri ·ms that ·how quari ·b cro .'cction. The clongntion i · p~tra ll I t 

tb crrtallographic axiH a and corr ·ponds to the ftx is of le<l.-t ela -tit.i t,y . Th se 
15 PETROGRAPHY OF OR TER LAKE NATIO AL PARK. 

lend r pri m ex ingui h paralle l a,nd exhibit th u ual r fra tiv pr p ' rti · of 

olivine. A ' ction cut parall l to the brachypina oid di clo ed a neo·ati,·- bi e trix 

with large optical axial angl , the axial p lane being parallel to the longation. ln 

o. 1 1 one ection , ut o a. to how quari ·h eros ction, dis lo d in convero-ent 

polari zed light a bi -- trix with th e axia l p lane in a, diagona l dir ction. This ob::-~

vn,tion coupled \\·ith th fact that all ·quari h , ction. extingui h in th dir ti n of 

tb diao·onal, inclicat . that the pri matic habit i du to the cxten ion of the cry tal 

parallel to the a axi.' and that th form i · r ally th e bra hydom (021). Th "c 

oli vine how a. lio·ht conosio n, and have developed nnnow r ·orption rim of magnetit . They· often contain inclo urc · of o·la ' that ar blad( and n arly opaque 

with in lo d mao-n titc grain . uch gla in ·lo ure · ar ft n of irr g ular hap , 

but common!}- th y a rc a rranged in longi ·h forms tret ·bed parall 1 to the elongation of the cry tal. Tb ~e long inclo ure do not xtend th whol l ngth of the 

cry tal. They arc more apt to be in the nt r of the r stal and, wh n e n in 

cro · section , arc square, th de ~ of the inn r black sq uar bcitw para!! I to th 

d of the cr t~t l. Thi · appearance i · 'rery ugge tiv of the black .-quar · to be 

·e. n i n cro · ection: of chiastolit s. 

A ' DE IT! ' BA ALT , TYPE B. 

Thi is repr ntecl by tbre »p cimen coil cted 2 or 3 mil wc' t and northwest of R d one. They are distinctly andesi tic in app a ran ee, being gray . mth<'r 

compact rocks with numerour:; but ·mall and incon pi nouR p lag·i claR plwnoC'rysts. 

The might r eadily be taken for uncle ·ite., but. a..,idc from certain difl'cr nc · in 

::;tru ·ture that alon might not be leci ive, tb ir a ·ociati n with di tinctl.r ba alti 

rock may j u tify tb i r h ing la s d under th ba ·altl . 

nder the micro:copc th groundmas. i · quite dift r ent from type A. One 

sp cim n (1 3) i appar ntly bolo ry-tallinc, on (1 ±) onktin · a v ry littl and th 

third (1 5) quite a per ptiblc amount of gla . The holocry tallin pe irnen ba a 

o-rounclrna ·ompo:ed of minute pri matic ery tal of auO"ite . o tab dral magnetite, 

and abundant plagio la··c. The phLgioclasc con i ts in part of di tinctly recognizahl 

lath· much smaller twd Les.- w 11 defined than in type A al ·o a ort of r ·idual fe ld-

::;patbi<: pa ·te that do . not show di tinct f rm and can not b clearly demon tratcd to 

ha,·c poly ·yntb ti ·twinning. It ha , howe\' r, a more or les undulou: xtinetion, 

and re ·emble the f ld path ic r esidual pate of ·orne of the ande::;it ::;. Tn th mor 

g la.- ·y \tari ty the augite is not o abundant, and th piao-ioela. appear;; Louded and 

indi ·tinct becau e of the du. t.) -looking gla . that impreg nate the whole, but till 

can no be p lain ly r ogn ized. 

Ph nocry · ar abundant and well formed. They are plagiocla ·e, hyper th ne, 

augite, and, in th ca - of. o. l 3, oli vine. T he p lagioclase i charactcri ti ally ancle-

: iti<.: in type, bowing zonal stru tu re and conta intng in losure · of hyper thene, 
BA ALT. 159 

mag netite, and gla. s in it' accu tomed di tribution. Hyper. th nc and augit ar 

in harply defined cr tals, xcept whe r they o ur in nests, which i ommon ly 

the ca. . Th y have the ·olor and pleo hroi ' m ommon t the ·e mineral in th 

a nde ito . They both contain inclo. ure of co lorle ':' g·Ja,s with air cadtics, al o f 

mag-netite. Parallel g rowth of augite around hyper. th no alii t' o of th so (1 4 

and 1 ' ) to th e l a. al . The olivine of No. 1 3 i not n,bundan . It o ·curH mo ' tly 

in g rain :tn lin rounded forrus with magnetite rim ' . :Magn titc oc ·ur · in the u. -

tomary octahedral cry tal ·. 

A, DE ITI BA ALT , TYPE . 

Tbi i p rhaps, the leru:>t ande ·itic in appearanc and the lea -t de ·er ing of 

b in o· cla ifi ·d as a di tinct type of _a ll the ba alts of th i r egion. Tb two pecimen ' that b long- b r (1 6 and 1 7) wer olle ted from tb ba ' alti ro k tb 

xtrem ·outh1Ye tern part of th mapped area., about 1 mil from N . 1 2. " 

th es two ·p ·imen bear t ·Io r r e eml lan e to thi roc] , p rbap than t a.n. 

oth 1 one, th y may be lool cd upon a. a facial d · 1·clopm nt of The' e ar 

blackish-gray, very den rocks with a ba altic rath er ban and ' itic app arau ·e 

b ing apparently fro from ph noc r st.: . In thin . ection how 1 r, tb y arc n to 

ontai n nu111 r ou - IJut ·mall phcnocry ·ts of plagio Ja c with b road lath-forru, ·ugo·c ·-

tiv ' of a ba:;altic rather than an andositic t p . In addition to the c th r a rc only 

a few o l i ,. in and <tug ite (but no hypersthene) phenocryst · in roug-hly idiomorphi c 

or in g ranular form . The groundma::;H con i ·of a fe ld pathi pa. te thickly crowded 

with roundi ·h roughly pri ·matic OL' irregular augit grain:, and with mao·uetitc. 

Gln '. a1 p :11" to b wh Jly W<tnting; . 

.A DE ITI BA ALT , TYPE D. 

Tbi · typo iH pre min ntly ande iti u, ith r through the d Yelopmeot of plag-iocla c 1 b nocr · -t: or through the pre ence of an abundant gla .r ba . The 

rock her . r pro en ted ar con fin d to the Ia fL flow.: to the northwest of th e 

Jake. Nol'. 1 and 1 H conw from th a t rn ' lope of th e ond ·ummit north 

of De ·c rt 'on , No. l ( 0 com · from tho . ummit of the first bill north of D :crt 

'one tutd No. L9 L a. bout ba If ~t milo ·outb of th i:; ·am ;; ummi t and not far from 

th ;,:add l hctwc n that bill and D · r ' uc. Nos. 192, 193 a.nd 19± w recol lect d 

<lt, or not far from, th ·. 195 ~tnd 196 from tho nearly 

flat. r <•·ion we~t of Rod one. 

'l h ~ ha;,:fdt: ~n· dark to bla k d n c and partly 1 e icular ro k · with a mor 

lihoml d vclop111 nt of minute f ld par phcnoury ts than i · tho ca ·e with mo t 

of th e oth r a nde i ti ba ' a l . I n spit , how 1·er; of th d i tin ·tly and ·itic type, 

thes ro ·k. , h'cn examined und r tb 111i cro. cop · a re . een to be a im st ontir · 

free from the larger, ·tot tt p lao·.i o la ·o phenocry:;k that ar o charact ri ti · a 
160 PETROGRAPHY OF CRATER LAKB NATI AL PARK. 

feature in mo t of th e aud site , and that mn.y so be een occa ionn.lly Jn orne 

of the abov -de ri b d basal . 'ertainly th y ar fr f rom all r "Orptioo ph -

nom oa and from the int rmed iatc ·loud d zone chara te ri ·ti of th larger 

plagiocla phenocry ts of Koi< . 179, 1 0 rtnd 1 1 of type 1\. In fo rm they are u nrtlly 

r ctaog ular or broad lath cd, and they var} in izc from on -half m.illim t r 

or even on millim ter down o h micro··copi · lim n, i n of ·b g-roun dma · 

lath ., Thor i ·, in fac t, no ' harp lin to be dmwn bet,re n th plao·ioclas s of 

the o-r undma ·. and of th I henocry."t". Th y vary oTeatly in th haru ·t r 

and amount of inclo ure . t tim t h e nte r · a.re thickly rowel d with itT gular gla s inclu"ions; at tim th gla · in lu iom; a rc catt r d or en altog ther 

mi "iog . Le commonly one may note inclu ion " of h p r:then or of auo·it . 

' Vhile plagiocla ·e i · by far tl e mo t abu ndant ph no ry ·t, the pyrox nos 

ar al o abundant. The ·e ar e u "ua lly well d0 \

7Clop d, ·p ·ially in , o. 196, and ba ve 

th n tomary propertie already fr qu otly de ri b d. v'\ ith tho xc ptioo of 

the thre p cim n from Bald Cratnr (192, 19 19±) hoth augite and hype r. th n 

are pr ent. In th e three . p cimen hyp r then ould no he foun 1. n the 

other hand oli\ine a " i u' ually the ca wh n hyp r -then i · ab::: nt or scn rc , 

i · much more abundant than i the a 'e with the oth r ba alt; of t. p D. The 

py1·oxen . , bowev r, fluctuat gr eatly in amount and in d finiti n. In No ·. 1 Ui., 

190, and 191 hypcr 'thenc i tho more abu ndant, th - aug-it b in o· almo t confin d 

to the groundroa ·. OliYine is ncnr entirely wanting. but it ~ l'OII pi uous on ly 

in t.h thrc t·ock · jut rcfcncd to. In the ' ' it i: 11 t alway · ca ·y to di:-ting-ui b 

b twe n th oli,-io ' and the ,-er}- lio·ht gr n augite. a ' tho color i: a lmost alik 

in the two. Thi · difl:i ulty i greater in ection. of oli\"in that ar ut n arl.r 

perpend icula r t one of the bi: ctric , a · in th is ca. e the interfe rence color.' are 

no high r than in augite. Th mo ·t co n picuou · form d ,. loped is the brachydome (021), in addition to which th re occur ~ eithe r ct pri m r a t)inaeoid. One 

'ection cut perpendi ·ular to thi, brachydom gave in th c nt-,. of tho ti ld a 

po. itiv bi ectrix with larg optical axial angl . Th trace of th . ides mea ·ur d 

2° , which is about one degre larger than i · giv n for the ano·] • of the brachydom (021). · 

The g roundma · of the ·e ba altl· co ntain. not a little g la · whi ch i ithcr 

brown or i: colorl e but r endered brown by th pre ·ence of du t-lik <' g lob11li tic 

material. This browni h g la ·s i thickly crowded with minute augit pri ·m · and. 

to a much Les: extent,, with magnetite a,n l with plagioclase lll ierolit :;, the last 

mt111ed heing, in £act, almo ·t abs nt from tho Bald Crater ba,·alt. 
l1A' L'.l'H. 161 

CHEMICAL ANALYS ES OF BASALTS. 

The followin o- ft nah. ·.·e:; 11'"" 1' 1 1 I"CJ" · tl l ' 't ! "-'t t 1 · a .t -., 111 10 111 'C'( o a ,(':-: :reo og1ca l ~lilT y 

laboratory: 

. ________________ ___ ___ ___ __ ___________ _____ _____ . ___________ _ 

Al, 0 3 •• ________________ • _ ____ _ ____ _ _ _ ______ _ _ _ _____ __ ____ _____ __ _ 

Fe.,03 

• .•• ____ ____ ___ _ __ _ _ __ _ ________________ ____ __ ____ _ ____ _____ _ 

F eO . .. .... .. . .... ... . ----- --- -- -- · ··-- -- --- -----··· · · · ·· ........ -

1\'fgO .. _ ... ___ __ ... .. _ . .. . _ ... . _ . . __ .... _. __ . ... _ ..... _ . . ... : . .. . 

CaO •. ... ........... ... . . ......... .. ..................... . ..... .. 

;\la O ___ .. _____ _ .. ____ . _ . ... _ . ... . . __ . __ . . . ... . ... .. . .... ___ . .. . . 

K20 ......................... . ..... . .... ... . .............. . ..... . 

H20 - .. ...... .. ..... ..... . ..... .................. .. .. ........ .. . 

H,O-l -·-·· -· --··-- -- -· -···· · -··· · · ·· ··· ···--··-·· · ·········--··· 

'l'i 0 2 . --... . --. .. -. -... -----.. ..... . .......... -. ... --.. -. -. --. -.. 

iio.\lii 

18.84 

:l.06 

4. :., 

4.3i 

1. -r 

:3. !) 

. ( 2 

. 1!1 

.:)1 

. i!l 

ZrO" ... . . . .....•. ...... . . .... .. .. ... ···--··········· ···-···--·· · · ··· ·· · ··-

·o2 .. -.. .. -. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . e. 

P,0 5 ••••••• • • _ • • • •••• • •• •• •••• .•• .• ••••• ••• ••• ••• • ••• _ •.•••. • _ _ _ . 19 

I 

Os ...... ··· - ·· ·------·- -·· · ·· ··- ··- ·· ············--··· ·· ·-- -· · · ----·- . .. . 

I ---- --------------··------- ----------- --- ·· ----· ····· · · ·------ _____ _____ I 

F ---------- ---------------- ----- --·---- · · ---- · --------- --- ------ ----------

Trace. 

N~~> :: :::: ::::::::::::::::::::::::::::::::::::::::::::::::::::: . -- :~ ~: .! 

l\[nO ... . . . ... . .......... .. ......... .. ........... -- ---· .... .. . .. . Trace. . J:laO ... ... ... . ............... . . ... ... ... ... . ..... . ... .... ....... . . 04 

,'rO · ··· ·· ········· -- -- · · ----·-·-········ ··· ···· · ··- - -- - -- --·-··· 'l't1-l('f'. 

I i:{. 

5:l.H\l 

16. il 

3. 0 

3. 5.') 

6.95 

-~9 

3. 56 ' 

1. 29 

~ nc. 

Xo:Jc. 

. 4:l 

~on . 

Trac. 

ndet. 

~on e. 

i'\one. 

. 02 

'l'r·aL·e. 

. 07 

. 12 

Li 20 !\one. ~on . 

'r o ta I ....... _ .. ___ .. . . __ .. ___ .... . .. .... . . ........ _ .. .. _ .. _ - 100.1 -,- 99. 92 1 

No·r·B.- 0= l. 

18\l. 

ii8. (),' 

~8.:)5 

l. 59 

4.:ll 

3.-!1:1 

6.95 

3. 70 

] . :~2 

. 20 

. 70 

. HI 

None. 

.17 

Non . 

·one. 

r one . 

Trace . 

. 06 

Tr-ace . 

None. 

100. 20 

;\lo. 15 . A hyp rsthcne-b aring h<~o;alt of the inte rstitial typl', frorn Anna Creek. Hee pag l-15. 

No. L73. H y1 e rsthe ne-bearing basalt, porphyritic interstitial typ·, transitional ~ tho Rndesit.i · 

typ , front tbe lmf:e f R od Cone. F;ec pa!{l' J5'. 

No. 1 9. h y] e r t he ne- b a.l'in , ha. •lit, of lire and • it ie t.yp•, fr 111 north of Dc::;e rt Co n •. 'l'hi · 

rock is doubtfu.ll y I la ed among t he ba~ll , ba ed u pon tructu ra l and geologi ·a! r latiou i.Jip . Npc 

page 160. 

9255-No. 3-02-11 
16~ PETROGRAPHY 0.1!' ORA'l'ER LAKE .A1'IO AL l'.ARK . 

CONCLUDING REMARKS ON BASALTS. 

At thC' time th ::;('rocks wc rC' :<t udicd no ana lysi:; of the ande~< c typeii of bai'Jalt: 

had !)(' n made, and tlw rod;:,.; we rC' nau1ed in accordltn<· with th ir stru 'tural 

f aturcs. In ind i,·id nal ~e::; the res mhlftncc of tbe.· ltnd iti l· h11:;alt of typ 

D could not well he i~<tir ui ·h d from cert.-'lin of th e ' mt r Lake and ·it ::;. It 

wa · only h_,. Utking a ll the sp cim n:; :oil ted from a particul a r ,. lcanic nt r 

that the real differcnc ' cou ld h made to ftppcar. Th ' surrnis tlHLt tb e:-~' ro ·ks 

a rc n arly if not qu ite th e qu in1lent of th a.ndesitc,;; is ho rn out h an analy .­

ruade later ftnd fo und on page Ltil. This r o ·k, No. L !-1, ·om s from the !a nt tiow 

northwe. t of the Pumi ·e De ·ert on th xtr me no r.th €'rn dg of he ar a mapped. 

Tb analy.-is is not fM difhr nt from tb aY rage analysis of th 'rat r Lak 

and it s. lt i::; ,. r.v ·lo,;ely .- irnilar to th amtl!·:; i,.; of tbC' ande ' it No. · l. g i,· n 

on page !l±. 

F rom a ·ompar i,' On of the:e anal_y::;c: it is (' \·id C' nt that ch rni ·ally th r i~< no 

mark d distinetion betwe n tbi::; an de. iti ba:;alt tLnd ::;om of t.h ro ·k · that may b 

·on ·idered a · true ande ite ·. 

If thi · in d.i\'idual rock ~<fLr.np e could w II b ·onsid red apa rt f rom the 

immed iately ·urrounding rock::: it should be de.-ig ntLt d a.- a n andC' ·ite b ut the 

pr pond rating eviden e ·eem · to point to the genera l rock rna ·.- fr om wb i h th i · 

wa taken b irw a ba alt. 

T h fe.'1tur s t hat di:< ting 11i;.: h th 0~ ro ·k,; fro 111 t u ' a11 lc:-~ it '>-~ arc lir ·t, tbe 

auundan ·c of olivine whi ·b, tbou,·h ,. ry tluctuating, i . a. n a rly <.:o nstant irw r ed icnt, 

·upplanting in whole or in part hypersth ne · : · nd the fr quent di app aranc 

of th hype rsthene · thi rd, the relativ ly g reat r abundance f augite both among 

the ph nocrj : t:s and in th u- roundma.- · and in the latte r ·a. , their Teater : iz ttnd 

le distinctlj mi ·rolitic fo rm· fo urth the omptuati•e :·car ·ity of a gla ·y ha ·e ; 

fifth, the gT ater abundan e of rnagn etit . 

The basalts of 'rater Lake of all t ·p ' are, li k the a nde ite a nd da ites, 

a lmo ·t complet ly unalte red. "\iVith th exception of oli vin th inoTcdi nts are 

app~ · ntly a::; fr ::;h a · when fir. t formed. The only fo rm · of alt ration in the 

oli vine a::; far a noted arc the partial · rpentinization and the d Yeloprn nt of 

rnagn tite a nd hematite. The d velopment of th homogeneow; pseud mo rph s 

lLftcr oli vin e, de· ·ribed by Iddings from :om what . imilar r ock::; in th Eureka 

district, evada,c• a nd named idding itc by L aw, on, b have not here be n noti · d. 

The hyper. thene-bearing ba ·al of the Eur kn. di.-tri ·t, N mda, which have 

b n de:crib d b Mr. Iddings in the rn onoO'mph jutlt above q uoted, appea r from 

«Geology or the Eurektt di ·tri ct: Mon. · . .'. Gcol. Survey, Vol. XX, l 92, p. 3li7. 

b Bull. Dept. Gcol. liujv, C(llifornin, Vol. 1, pp. 31-36. 
BARALT . 163 

Mr. IddinO's'~ d scription to be ·lo ly related to the basalt; f ' rater Litke, 

more c p cially, howe\· r to tbc ande:oi ic basaltr xc pt that the Eur kn. di;;tri et 

ba ·:dtl:l ftre rnu h 1 . ' fold pathi<'. t only i:· the O'eneral chn.rMtcr of th -

oundma.· ~ th srun , but a l o th e I .vrox n x 

corn 0 in with th di. app ftrance of hyp rsthene. 

r lation hip of the O'enc rall_,, old r hyper.·th e- ne 

and the flu ·tuating oli vinr that 

Furth rmor r;nay b notrd the 

to the young r augite an I th 

pam! I l growths of aug itE' around hyp r. the-ne ph <:' no rysts, which i an almost 

univer a l ocC' urrenee in the Crater Lakr basa lts of all type. . Compfl.ri' on may 

al ·o be mad with th quartz-bcfLrinO' bn alt of Cinder 'one, north of Ln.s n 

P ak, in north rn 'n.lifornia, d .·cri bed b.' Mr. D ill er in n. paper on A Ll\t Volcani c Eruption in North rn California and its P ec uliar La\7 fl." With the xC'eption of quartz , the re mhln.nce is qu ite clos . ?11ore e p cially ma) b m ntioned 

the magn tite rim · around tb oli vine cry:t.. Is and th plagiocla. e pbeno rysbl 

with their fr quently corroded fornr a nd gla · inclu:·ions as well a. the d v lopment of the monoclini and orthorhombic PJ'l'OXen . 

u Bull. l'. . G ol. urvcy Xo. i9, I 'Yl. 
164 PETROGRAPHY OF CRATER LAKE N A'l 'lO A], PARK. 

List of Gmler Lake 1·ocks in the order in 1chir·h they are clt•sr..-ibt'Cl in this paper, yicinr1 in each rase th cu1-re- . sponding original number. 

l. ... . . "I :27 

2.... .. 12, :{._____ 1::!2 

4 ---- - l-12 

ii . ___ .. I 14+ 

G ...... 4, -1 02 

7--- -- - -1 , 409 

ll ...... -1-, -11.1 

!) ----- 4, -11 2 

10.---- - 4, -1 21) 

I I ...... -1 , -1-:'15 

12.----- 4, -1--1-4 

I:L ..... 4,-H4 

1-1-. ----- 4, -1 76 

I fl.----- -+ , 477 

16.----- 4, 480 

17- - - - - - 4, 497 ,, -- ---- 4. 52fl 

I H ..... . 4, ii:~7 

20-- ---- 4, 53 

:.1 1 .. -- -- 4, 5.'i8 

22 . -- -- - ] :30 2:~ ..... _, 1 r 

2-L . .... 4, 40 

25 .. ---. 4, 4::!3 

26 .. -- .. 4,-150 

27-- -- .. 4, -1 6-1 

2 4, 495 

Z9...... -1 , 50:"1 

HO.. .... 4, 5:~9 

:31.-- --. 4,5-lfi 

X2. .. .. . -1 , ii55 :~:~ .. -- .. 4,'-7 

::! +. ----- 126 

~"> ---- -- 13 1 ;~ ti...... 143 

:n...... 146 

X ' .....• . 4, 396 :-;fl __ ---- 4, 396, c 

40 .. __ __ -~ . 404 I 

41 ...... -1 ,407 

42.- .... I 4, 410 

-1 3 ..... . 41:~ 

44 ...... -1-,.JH 

45 __ __ __ -~- -~- 1.5 I 

46 .. .... 4,416 

47 ...... 4,41 

4 . -. . .. ,4, 436 

49 .. ---- -+, -1 5 1 

50 .. .. .. 1 4, 465 

51 .... .. 4, -llitl 10 1 ...... 1::):{ 

52 ..... ·I +, -167 102 ...... +, 420 

5:~-----· 4,-172 10:~------ 4, -1 21 

54 ...... ,475. "10-1...... 1: 4 

-- 4,-1 4 ll lo.-....... 1 4, ~o~ 56 .. .. .. 4, 5-10 J 06.. .. .. 4, uO-J 

f\7 ...... 1 4,5-1-$) "107 ...... -l ,ii (i 

i) .... -- -l, 556 108 .... -- 4, 507 

-9 ...... -1 ,::!!16, f, 109 ...... -l ,liOl 

60 ...... 4,-103 11 0 ...... -l ,f\02 

61. ..... t 4 4:)4 Ill . .. .. . -1 ,560 

62.-.- . ·I+, -1-1:{ 112 .. -- .. 4, 56 1 

rH ...... -1 ,45.'i , n:L .. ... -t ,5H2 

6-L ..... 4, -1 7: Il-l ...... , -1 , -1 94 

65 ...... -1 , -1 83 115 ...... -1 ,4 1 

66 . ..... 4, -1 90 11 6 ...... -1 ,-1.2 

Ill ...... 4, 4!12 117 ...... -1 .j,'li 

·,• ...... . ~~(j I' IlL.--. -1-, -1 87 

H\l . ..... 4, .'J.ifi 11 !1 ...... -1 ,-188 

70 .. ---- -1 , ii-lii 1~ 0 .... -- 4, -l "!l 

71 .. .. .. 4,5ii!l 1 121 ...... -1 , -1 57 

72.. .... -+ ,~6 ~ ~~------ -1 , -l!i 

73 .. .... -l ,u6-l ~------ -1 , 460 

7-1 ...... 4, 56(\ I J 2-1 ____ .. -~- . -1 61 

75 ..... . -1 , 429 125 ...... 4, 468 

76 ...... 4, -1 62 126 ...... 4,-169 

77 ...... -1- , -1 7$1 ! 127 .. .... 4, 471 

7 .. .... -1 :39G,a i 12 4, 470 

79 ...... -1 , -1 2-1 ~9 ...... -1 ~2~ .o ...... -1 , -17 130 ...... 4 :)-I f 

J. ----. 1 ii2 13 1 .. -- -- I -1 , 5-I 

2 ... ... 1 lii3 1:32 ...... 4,iiii2 

3... .. . lii-l 133 ...... 4 ii5:~ 

15- 1:'14 .. .. .. 4,39!1 

lii6 1:15 ...... 4,54-1 

157 136 ...... .J , -1 22 

15 137 .... -- 137 

15!1 13 .... .. 4, H!l7 

160 139 ...... -1 , 499 

16"1 140 ...... 4,52 

-1 ,55 1 141. ..... 4,39 

92 ...... 4,536 J-1-2 ...... 4, -117 

93 ...... 4, 536, ft 143 .. ---- 4,-123 

94 .... .. , 4, 41 9 l-1--1- ..... -1,459 

95 ...... 4,550 H 5 .. .... 4,500 

96 ...... , 4,55-l "146 .... .. 4,49 

97...... J29 H7...... 147 

9 .. ---- -1 , 463 l4 .. .. .. ]4 

99 .. .... 4,-10.') 149.. .... 149 

JOO .. .. .. 4, -lOG 150...... 150 

15 1...... 15 1 

152 . ... . . 4, 52"1 -

153...... -1 , 5Z2 

154 .. .... 4,523 

155 . ..... 4, 52-1 

156 .. -- .. 4, -10 1 

157 ...... 4 "0 

158 .... .. 4: -1 2() 

159 ...... 4, -1 2 

160 ...... 4, -1 3 

16 1 ...... 4, 4-1 2 

162 ...... -1 , 430 

163 ...... 4, -1-1 5 

164 ...... -1,-1-18 

165 ... --- -1, 509 

IGtL ..... ·1, 4-1-9 

167 ...... -1 , -l ii 

168 ...... -1 ~w 

169 ..... 4:5 17 

170. . ... 4, 446 

17! ..... 4, -1 5(; 

172--... -+ , li27 

1 73 .. --. 138 

17-1 .. ... 18\l 

175.... . -1 , 400 

] 76 ..... 4, 5:32 

177 .. . . . 4, 5:1:3 

17 .... . 4,447 

179 ..... 4,-152 

180 .... -- -1 , -1 58 ., I. .-- .. ' 4, -1-'i-1 

I 82.. . .. . -1 , -1::!9 

1 0. .. .. . +, ;:;z;, 

I

I 4 ...... -1 ,5:31 

185------ 1 4, 5::!4 

I 6 ..... . 4,-1-10 

I '7 ...... -1,-1-11 

1 8.. .. .. 4, - II 

1 9 ...... -1 ,5 12 

190. .. .. -1 , :~ 

1.91. ..... -1 , -14 

192 ...... 4, _518 

19:L ..... 4, 5 1!) 

194 ...... -1 ,520 

1 195 ...... 4,52(l 

196 ...... -1 ,5:~0 

197 ...... , 136 

J9 .. .. .. '1-1 0 

I 
J TDEX . 

Png-t•. 

Ager, Cnl. , r out to Cmter Lnk from.. ............. 7 

A udesitc•, areas of ................................... :!3-:ll 

augite in ... ....... .. . ............................. , · '~ 

·h mica! analy.·e. o f . ... . ............... . 

clas.~ ifl nti n of . . ............................ . 

mpon nts nnd g u raJ futtnres of. .. . 

crystals in, p1!1te showing ........... . 

dnciti · typ of ...................... . .. . 

dikes of ......... . : ................ ......... . 

gin inclosure. in . .... . . i l 

h mntite in ................................. . 

hoi r ystnllin typo of .......................... . 

ho•·nbl nde i11. .................................. .. 

h ynl opiliric typ of ............................. .. 

hypo<·rystnlline type of ....................... .. 

tnagnetite in ........ -------- ........ ------ ....... . 

1nin r a.ls io~ thin e<' ti ~ of. ________________ _____ HR 

OCClliT nc of ......................... ........ 2: :11 

oli\·in in -----------·----------- . . -------· .... -.... tt:J 

pyroxene in ....................................... i i'-R:J 

quartz in ........................ .................. ~) 

secr oti us in . ....... .... .......................... ~t'i-llll 

p latoshowing... .... ............ .............. flli 

thin f<OC tions o f .......... .... ...... . .. .. .... . .. RO 

tl'irl ymite in ....................................... ll:i 

Andesit'i e lm,.t!ts, o<'emTetH'C 1\nd ehaJ11<" t or f. .. 1.·,1 100 

Aunn. r·oek , and si nr as noar -------------------- 2n 

n.nd f;itO fro m n onr, dtara(" t rsof -------·--- ___ \Xi 

bnsnltfromncar ................ ........ .... ...... 14 1 

gin intion ncar ................................ ~I :?.~: 1 

jointed tuff of.................... .. .. ...... ...... 4:t 

Apntito in basalt. o cui'I'Cil<'{' nnd chnmcter of ... Hf• 1~-0 

As hland sh et of U . ·. topogmphi<' atla . 1u· ' n 

mnppcd on ................................ 5 

Augites, cb>U·ncter of ....................... 1!2-&1, )(14 , 143 

Bald rf1t r . nndc><itic basalts from ............. .... HiO 

bnsaltat.............................. ...... .. ..... :!3 

Basnlt , nnd ·sitie, ·cnrrenco 1\nd c haJ11CtPr of. . J.jij...ltiO 

apatite CI'YStnls in ..................... , ........ 1~: 14G 

arcnsof . ........... ............................... Rl -'14 

rLUgite of ......... . .... ...... .. .... ........ ........ 143 

ch mien! nnalyEis of. ............... .............. JGI 

cr ystals in, plate howing................. ....... iti 

feldspar of ...................................... 14'' a 

bype r·sth nc f ...................... .... 14:3-144 , 145. ·14i 

int r titinl, ·curr n ·e and c-llllmc te rs of ..... H 1- 15G 

mngne tite of ................................. ..... 14fi 

oc ul'l'enc ttnd chnm tors of. ........... 31 34 , 141 - 163 

olivine of. ............................ ..... ...... I~ 145 

ps udobr kite c ry stals in ............ 14'- 146, 147- 14 

thiu scctionsof................ ...... .............. 138 

13om· reek, dnc it nell!' .... .......... ................ 36 

g lndal d 1 it s net~r .............................. 41,44 

nmping pin ·e ncar Crn t r Lake, d script.ion of .. 8-9 

Pnge. 

< 

1

asuule Rang-C', foundat.km ,f _ .... -- -·-· ___ --------- 17- 10 

limHs of . .. . .. . .. . .. . .. .. .. .. .. .. . .. . . . .. .. .. .. .. . 17 

YOlca.uie con u . ....... --------··-·-····· . ..... G 

\'iow sbowing ......................... ---·-- td 

Oa .. ~t e 'ro k, nnd site iLI'f•a.ncn..l' ..................... ::?fi 

glaehLI deposit; nenr .............................. 42 3 

nf<tlo '1·est, andesite nt. .......... .. ...... .......... 26 

0 1 c twood ovc. dac it Itt .......................... 3.'>-39 

clltcite from, dll\l'll{'te r or. .. ............ li~ 11 3 

lava. n ( )'\\1 nt, vit' w of ...... ----- - ···-··· ------ 38 

topogmph y or eonn try II<'H I' .. ..... ...... .... .... 9 

,-oknni(' rO<·ks nt .... . ......................... . 

('loud llp, dnr·ito at ....... ....................... 8,3:.>-36 

dn.ci te f1·om. ('hllmf'ter c•f ...................... 1 14- 1 W 

rlik near ...................................... .. .. 31 

glnl'intion noo1· ............................ ........ 41 , 44 

0\"dll e, li". v., gng"ing of C'riltPr' Lake by _____________ r,r. 

Cmtcr Luke.1U'M of .................................. 22,60 

bedof, v-iew show·ing ............ . --------------- 44 

chang gin love! of.............. . ................ r; •7 

c rusta ·et~n life of ................................. M 

diS('ove ry of. r f •·eru·o to ... ...... .. .... .... .... 5 

dminn.g i<roo of ...... ............................ iii) 

evnpot·a.tion fr·om ....... ...... ------------------ -- !i7 r.9 

x ursion routs ft·otn ............................ 9 

geolog ic mnp of. .......................... .. .. .. .. 26 

inflow of ...... .................................... ;,~-{J() 

levol of,chnnges in ....... ............ ." .......... rwH;7 

location of .. .... .. .. . .. .. ... .. . .. .. . .. .. .. .. .. .... 6 

map showing r out JS tt>. .......................... l 

map, g logic. or .............. ..... .............. 26 

origin of ... .............................. .... ...... 46-..'iO 

outlot of ........................................... U0-61 

rim of, genernl features of ....................... 21-22 

r outes to .... ....... ............................... G 

map . bo,ving ......... .... . ........... .... .. .. JS 

tempomture of ........ .......................... . 5I :.:1 

vi ew of mode l of basin of .... .. .... .. .... .... .... 44 

'' iew or rim of .. .. .. .. .. ... . .. .. .. .. .. .. .. .. .. .. .. 2\1 

vi ews of ......................... lH, 22.24, 2il,::o,:Jt;. :I>!,M 

rl\ter Lake N1ttionnl Pnrk, ne t establishing.... .... ;, 

bo unda ries of ........ ........ .. ....... .. .......... :i 

geologic mnp of................................... :tO 

mnp of .................... ........ ...... ..... . .... li 

map showing location of ............ ............. ~ 

'mter Lnke. pecinl sheet of U nited . tntes topogrnphicatlns, urea mnpped on ........... ;, 

mt r Pet~k, 1mde itic b>lSalts fr·om ............... J57-15S 

bnsaltn.t ............ ..... . ...... ................... 311-34 

re tuceons history of tb nscnde Range, k tch of. 17 J~ 

Dl\c ites, npntito of .................................. 104-lt)r, 

nronsof .................................... 34--4l.99-HXI 

augite of .................... ........... .. ......... Hl-1 

chnrncters of .................................... !JI)-]41 

1G5 
166 l DEX. 

J..IHg'l!. 

Dac ites, chemical analyse of---------- ----------- - J40-14l 

c ry. tals in, plM<' showing . ·--- --·-- -- ---- ------·- 76 

dikes of·---._.·-- ___ ___ .. .. . ______ .. .. _______ . :1\J, 121 ~:1 

f ldspar of -------------- --- --------------------- 100-1(!2 

hornblende of. __ .. .. ____ ____ .... ----- -_ ..... ---- ]{!2-104. 

h ypersthene of ________ ------ ____ _ -- ---_-- · . . ______ 104 

occurr n ·cof ------------------- ----------·------- oli vine of ____ _ ........... _ ........... ----- --- -- ---- 104. 

socr tioosin ------------------------------------ 125-140 

thins ctions of -------- - --------------- 121l. lJI2, 1a8 

thin sec tions of minemls in ------------ ---- 128, I:JS 

tridymito of. -- ---- ---- ---- ---- -- ------ -- -- -- ...... 10'2 

zircon of ---- -- -- ---- -- ---- ______ _______ ___ __ ____ 104-lllii 

Dac iti oj c tam uta, O('CU IT n<" and <"hnrnctor 

of ----- ------------- ---------------------- 12: HO 

Da ·iticpnmi·o, c nrre ncoof. ........... ..... ...... 3!l I 

Dacitic tuff, occuJTen e and characters of ___ _ ------ 1:!1 

Dange r Bay, dn<"iti pumice n a r ________ _____ ___ ____ 40 

glacial gr1n-el nea r ---- -_ .. ___ ..... ____ ___ ----- __ _ 40 

Davis, W. l\f., c.ited ----- --- --- --- -- -............ ------ 29 

Dead Indian r oute to Cr nt r Lnko, c m--o of....... . 0-i 

Desert C ne, andesitic b>~.S~Llt . from near .... _ .... lft.J- 160 

bn.<;alt a _ ----- - ______ ------ _ ......... -----· ...... 32-3:3 

l!Lva from -- ------- ------- -- ----- ------- --- -- -- -- ln2-1f>3 

Devils B>Lck bone, dike at_ ___ _____ ____ __ -----------·--

featur es of ___ __ --- -- ___ _____ _____ ----------- ------ 00 

view of- ----------- --- --- --- --- -- ------- ----------- :!() 

Diamond Lak , basalt from near --- ------ -----. .. ... IH 

Dikes, nndesitic, cha racter. of rock of -- --- --------- 92-94 

OCCUlTell ·e Of -- -- ----- ..... ..... ...... ---- .... 3()..31 

da.citic,occurr n ·eof ---- ---------------- --- --- 121- 12:1 

occun enc of- ------------- - ...... _----- 8,30-:ll, 121-128 

Dutton, C. E. , quoted on confi g uration of hottom of 

Crater Lake ______ _____________ ........... . 

quoted onoriginof 'r!lte rL"kc. ----- -- --------

Dutton Cliff, andesite nt ____ ...... _ ........... ----···-

pum.ice near .. ..... ............................... . 

EagleCov , di.keat. ................................. . 

xcm ion r oute from . .... . ..... ------ -- . ..... .. .. 

Engle rags, ande iteat .................. ....... . ... . 

Eru t Palisade, view of_ ............ . .......... --- -----

E ·ene hi tory of th Cnscad Range, sketeh of .... 20 

Evaporating pan at Crater Lak , view of. ._.... . .. . 54 

Evermann, B. W ., ack-nowledgment to ___ ____ --- --- 52 

quoted on temperature of Crater Lak ___ __ . __ __ f.0-61 

Fe ldspar , charactersof .. ..... .... ........ 100-10'2,14· 143 

Fluidal inter. titial basalt , occu.rrenc·e and character of ...... --·--· .......... ............ HS- b>2 

Gla ·ial action, tra · s of. __ ___ ________ .... _ . ......... _ 41-44 

Glac ial strire, oc ·urrenc - of .. ___ _ .. .......... _______ _ 

Glac i r Peak, ande ite from dike near .............. 93 

glaciation and glacial deposits near --·-- ........ 4l 3 

view of _- -··· ...... ...................... ____ .. .... 2S 

G1·ous Rill, 'lacitefrom ....... .......... ... ......... 111 

H matite in andesite, c har>Lct ers of . ----·-------.... &3 

H er ·hb rg r, E. W ., gaging of r~r Lak by.... . (>.5 

Hillebrand, W . F., analysis by _ .......... ------ ...... !J.I-.9fJ 

Hornblende, chara c ters of ---·-- . _____ ...... -- -· 8:3, IW-104 

Hypersthene, cha1·a ·ters of-- -- ---------- 78-82. 104 , 14. 14i 

Hype rsth ene-andesite, !Lllalysis of ................... 151 

components and g n ral features ,,r_ . __ .. __ . ____ (l. 00 

giMSinclosur sin ....... . ..... ............ .... il 7a.i4 

m!Lgnetitoin ·----·-- ·-··-------- ------ --·-----· -- · i:3 

py r oxen in ........... .. .... .............. ........ 7 8:3 

Hypersth n dn~ites, analyses of ..... . . ...... . . . .. 140-141 

fLp!Ltite of- ------ .......................... ______ 104- 105 

augite of ........................ . -----.. .... .. .... 104 

r.:haracter >< of ....... ____ __ ............ ............ 99-14J 

Pngc. 

Hyper th n dMit s, dik of ... ________________ ___ 121 - 128 

feldspa 1· of ---··----·----····· · · --------- -··-- l'l()- lf2 

hornblend of. .... .............................. 102 104 

hn>e r theno f..... ............................... 104 

oli,·in of ·----- --··--·-- ----------------------- · --· 104 

seer tion in -- ---- ---- ----------- --- --···-----·- 1$ - HO 

thin secti us of minomls in ---·-· ...... ........ 128, :~ 

t1·idymiteof. ........ ............ ............ ...... JIM 

zir onof . . .. . .. .................. ............ ... .10. I(); 

Iddin1,rs. J.P .. quoted on O<·cm·r nc·o of tl'idymi t in 

r hyolite· -···-- ----- -- --- ----·· --··-----·-- ll 

Kerr otoh,and ite n ,.,. _______ __ ___ ____ __ _________ 27- 28 

charactersof ........ .. ... ... ...... ______ ___ __ _ 96 

KlamathFallsroute to rat 1·Lnko,,·ou1·"o f ..... 'l 

Kh•math H ot Spring, features of •ountry a t ........ 'l 

Klr•math River , ancient \•all y of. ................... 'l 

dam on, formed by volcani • ruption ........... 'l 

La\"ll fl w , do ,riptionsof .. ..... .................... 23-41 

Lithoidal dacite, occurrence and cham<·t rs of ... 100-107 

Llao Rock, andesite of.............. ........... ...... 92 

and sit from, chara·tersof ... . ...... ... .... .. . . re 

basalt from near -- ------- . ..... ----·- ...... ..... . 141 

dnci!;(>nt ........................ ,::16-.'Ji, Ho 111 , 121- 1.28 

da ite dikes at .. ____ ... ___ -·-·--_-··-- .......... 121-123 

dacite fl ow at ........ .......... ...... . . ... 8 

dik near ............ ---·----- ------------·· :30, 121- 1.28 

g lacifild posits n '"" ----·--- --·· -- ----··· 43 

pumice >Lt ......... .................... ........... 39-40 

charac te rsof. . ................ ...... .......... 124 

viewsof · ------- ---- - ·--- ------- ------···-··-· .... 24,36 

Magnetit , characters of ---- --- ---------··------ ____ A:J, 145 

M dfor d, Or eg., r out rat r Lake fr m .... ____ . 

l\forrinm, J . C., c ited onE e n volcanicd osit~< of 

J ohn D!Ly r egion .......... .......... .. .... 20 

Mioc n b.i tor y f th ascado Raugo, s ke tc h o f . 20-- 1 

Mountllfazama, compadson of. with Mount ,' h!Lsln. 45 

de. truc tion of. ____ .... ------ .. ................ ____ 46-60 

development of ................. ..... . ............ 4!)..46 

footur of ........ .......................... ...... 21-23 

geologicmap f . ........ ··--------------·--·-·-·- 26 

glaciation of --··-- --·· -- ..... .................. 41- 44 

Ja,•as of .. .... ____ ...... .. .. .... ... ....... .......... 28-41 

map showing ...... -- --- ---------· ·· .... ....... 17 

naming of.................. .................... ... 5 · 

or iginal condition of _ ..... . ... _ ...... ..... ------- - 4~5 

r toration f, view showing _ ..... ... ... ........ 44 

~l ountPitt,el va.tion of ............ ------------ ------ 7 

v ie'v of _____ ___ ------ -- ___ ...... . -- ............ ... . 

Mount Sh!LSta, omparison of, with llioun t llltiZ!LJUa. 4u 

Mount Thiel'!en, location, elevation , and g n r nl 

f atur . of ....... ................ ......... 20-21 

pumice near ---------- ...... --- ----- ·--- -- ---- ___ _ 40 

llfunsonPoint,ande 'teat...... .................. .... 26 

N eocene volcau.i a ·tivity, arc!Ll x tent of. .. ... .... 17 

Ni kerson, W. W ., gagings of (;rat r Lake by ...... &1,55 

Nodular secr etions, ocourrence nnd c ha1·nc ter of.. 109-111 

Olivine, character of .... . ............. .......... 83, 144-145 

Palach , C., report by, on ype~·st n !Lnd ps udoooki tec ystal~in basalt ............. 146-148 

Pln.giodase in by']>eJ'flthene-anclesitos, c htwnc te rs 

of ............ .......................... ... . 69-'18 

gi>Lss inclosur es ilL ................. .. . .... ____ il-78, 74 

plateshowing ____________ ............. .......... 76 

r esorpt ion phenomem•in ..... .. ... ........... . ... 73-74 

Pole Bridge Cr k, basalt near _-- -· - --- ---·--·----- · 34 

glacialdepositsnear .... ...... ................ . ... 42, 43 

Po1·phyritic iuterstitinl hn.<;alt, occunence 1\nd 

char!L terof .. ..... .... .................... l[J2 
1NDEX. 167 

P11gc. 

Pumice, chamcte1 · of . . . ....... . . .................. 124-125 

dacitic , occurrence of --------- ------------- ------ 39---11 

Pumice Dese1·t, features of ................. _.. ....... 40 

pumice from, charac ters of . .................... . 

sand from, c harac ter of ........................ . 

Pumice Point, dacite at ............................. . 

t"i w showing ···-····-··-·----····--····-····· 

P ud brookite in basalt, oc~n rr e and cbara ·ter 

of .... . ........................... 1-li;- 110. 14 7- 148 

Pyroxene in andesites, cha rac te1 of ............... . 

Quartz in andesites, characters of ................ .. 

Redclond Cliff, dacite at .... ......................... . 

dik S <Lt ... .. ...... .......... . .................... . 

Red Con. bnSilltat. ................................. . 

basalt from, c har!l(:tOJ'S f ......... 141. ~•'1 1'>1 . F 

camping pine near .............................. . 

dacitic pumice near ......... ... . . ............... . 

cba.rRcters of. ....... .... ..................... . 

Rogn Ri,- r. glacial dopo its near ...... ...... ..... . 

r u te to rater Lak along ..................... . 

83 

35-36 

31 

1&9 

9 

Rogue River r oad, ba.'lnlt nea t· .............. . ........ 34 

Round Top , andesite at. ...... ........ ............... . 28 

pumic from near ................................ 124 

Rngg d r est, dacite flow at.............. ..... ...... 8 

Russell, I. C .. cited ou e ,·apor ation fl'om Crater Lak . 58 

Sand r eek, nude .ite f1·om head of . ................. 00 

camping place near . . . .... ...... ...... ............ 9 

dacitefr m ............... ......... .......... .. . 119-120 

dac ite t uff from . . ...... .. .... . ..... ............. . 121 

glaciation on . ...... ...... ................ . ..... 42, 43,44 

cbmidt, S., flgm·e cited from . .. .. ................ 76,147 

Scott Peak, featm·es of. ...... ........................ 28.4.'; 

glaciation n ear .......................... .......... 41 , 44 

Seer lions in da ·ite, cbamcter •md oc ·nrr nee of .. 109-

Jll ' 139-140 

S ntiu I Rock, and ite dike at. ..... .... . . .. . . . ..... 31 

·bul'l\c·te•· f •·ock of --- ------------------ ---- 93-94 

ande ite sb t near ............... ................ 27- 28 

g in ·in! f{ J'ILV Is near ....... ................... .... 40, 4l 

pumic n ar ..... ............... ......... ......... 40 

!:)bol " · . R. , gngi ngsof rate•· Lak by ...... .. .... 54, 55 

phcrnJiti ' dacit , OCCUI'I'CIIl'O l\JJd •IJILrRCtCI'1 Of. J Q7- ]{)\) 

'tee!, W. G .. n know! dgmentsto. .......... . . ...... 47 , 

0 

Ptt,;C. 

el B<>y. <>ndosite<>l ................................ 29 

cbnrncter• of ............................. __ .. !l-2, 98 

dike a t. .......................... ..... ....... ... 31 

hn rnc ter of rock of .... __ . ..... __ ...... __ ... !l.-1 

tok , H. N , chemical ann lyses by .... 9+-9.'>. 140-141 , !til 

• UIJ C1· ek, J\ndesite ncar ............................. 27 

ham ·t J'S of.................... ........... ... !l6 

ducite near .................................... ... :15 

cha racters of ................. ............... II 121 

features-of ............ ............ ·................ n 

gla intion on .................................. 42. -1 !3,44 

'l,hielsen, 1\Iount, location. olon\.tion, n.nd gcn rnl 

features of .. .. .. .. ....................... 20-21 

'fimber 'm ter , basalt a t. ........................ . . :Ill 

Tridymit •. chi\J'ncte•-s of ............................ ·t 102 

Tuff, dacitic, occnnence 1\nd cha m c-tors of . .. .... 121 

Tunnel caved in, view showing _ ..... -· ···~ ---· ----- :38 

Turne r, H . W .. quoted on chnrnc tcr of hl']>or"thmll'· 

and site from Fmnklin Bill, Plunms 

Coun ty, Cal ....... .. ......... .......... ~ l:il 

"nion Peak , andesite at and near.............. ..... 2il 

gla iation n u·.. ..... . .... . ...... ..... ......... ... 42 

loc<>tion, elevation. nnd g n ml feMur • of ..... 20 

,-; wsof .................. ......................... ~.:i0 

Victor Rock, la inl deposit n u · .................. 41 

view of ........................ ................... 24 

VitrOJ hyl'ic dacite. 0<' ·urron ·e and ·ha•·a<·tCJ'S of. lOii-106 

Volcanic acti\"ity of Noocen p riod, ar ••I ext en t 

of ............................ .............. ti 

Volcanic cones, ·dews bowing ...... ··- -------··-- 1 .:Cl,:Xl 

w,.tchma n (Th ), andesit n t. ....................... 25, :)1 

ando itic dike at. ......... ... .................. 31 

chnmcter of rock of ......................... !l'l--9:J 

Wn.tchtuan andesite nren, dc~1·ipti n of ····---···- · 2:j 

Water g<>ge at Crater Lak , \·iew of. ...... .. .. ...... n4 

W tDeer Cliff,dacitoat. ..................... ...... ::18 

\Vilbnr, E .]'){., gagingsof Cnttor Lak hy ·····--··- r,.,,sr, Wineglass (The), dacite at ... .......... . ......... 8,:!7 · 

ch•u·a,·ter ·of. .. ... .. .... ............. ....... .11- 114 

Wi u u·dislnnd, ltndesit ret ........................... 29-00 

·l.uwnctcrs of ...... ...... . .. .. .. .... .. ...... !ll-92,99 

fentur sof ...................... .... . ..... ...... ,29-00 

,·iew. of ...... .......... ...... .................. 18, 24.30 

PUBLICATIO 1 OF UNITED 'rATE GEOLOGICAL URVEY. 

[Prof ionnl Paper . 3.] 

Th s rial pubUca tiOJr of the unit d tates Geological Ur\" y c 11 i. t of (1) Annua l Reports, (2) 

Monographs, (3) Profe: iona l Pa.1 r ·, )Bulletins, (5) :Jlincml R ·o tirce , (6) Water-. upply and 

Irrigation Pap r , (7) Topo,t-aphic Atlas f the nit d Rtate - [ lio and separate sheets there [, ( ) 

Geologic Atla of the 'nited tate.-f li thereof. 'fhe cia, numbered 2, 7, and ar · oil at -t 

of publication ; the oth rs are J.istributcd free. A cir ular giving con plet lists ma · b had on 

application. 

, The Bull eti n~, Profcs ional Paper!', and \\'at r-. upply PapC'rs treat of a Ya ri t.y of. ubje ·t.", and the 

total number is uecl i larg . They ha·;e theref re I ccn ria, ifi cl in to the following seri s: A, Eol omic geology; B, De cripti1· g ology; , 'y. t mati g-e lo"'y anrl prrl ontology· D, P tro" raphy and 

mineralogy; E, Cbemi. try and phyRic.; F, Geography; G, 2\Ji.· cllancons; 11, J' rc·try ; I, Irrigation; 

J, \ Vater to rag ; K, Pumping water; L, Qualit.y of water; ;.r, ?IJcthocls of bydrouraphi inve. tigalion ; , 1\ ater pow r; 0, Un lerground w:tt 1 ; l>, Hyd rographi c pro<> rc.•s r ·port . Thi paper i · the 

tw nty- econcl in f:i cri c · 13 ancl the lwcnt~·- first in • 'cries D, th comr lete li t of which follow. (B= 

Bulleti n, PP=Profe i nal Paper, W = " rater- 'uppl_v Paper.) 

,''F:ltl li, DES( HII..,. I'J\" ~ GEO I.OO Y. 

B 23. <'bser\'otions on the juncLion bc tw en th Btl te rn snnd$tono nnd the Keweenaw cries on Keweennw Point, Lake 

Supe rior, by R. D. Jn·ing nud T . . lHtmb rlin. 1' •. 12~ pp .. 17 pls. 

B 3;1. Notes on geology of northern 'nlifornin, by J . .'. Dill r. 1 6. 13 pp. 

B 39. The "PI> r beaches ond delta or Gln ial Litk e Agn osiz, by Wttrren Uphnm. 1, 7. s.t pp., l pl. 

B 40. hange in rh·er cour $ in Washington T rritory due to glaci>ttion. by Bailey Willi ~. 1 1. 10 pp., <L pi . 

B ~- The prc.•ent on dillon of knowl<'dgc f th e g ology of 'PCX>b', b)· Rob n T. II ill. 1, 7. 9-1 pp. 

B 53. The ge logy of Nuntuekct, by Xothnnicl. outhgttte. holer. 1. 9. f>5 pp., 10 p1•. 

B 57. A gcologic.tl rc onnni:sunee in sou thw<'stcrn Knusns, by Robert lin)'. 1 flO. <19 pp. , 2 pl . 

B . Th ghtciul bou ndary in wc8t rn J cnn yh·nnin. Ohio, K nturky, lndinml , ond Jllinois. by G'orge Frederick 

Wright., with introduction by ThonlJ.t Chr wd er hnmb rlin. 1 00. JJ2 11p., pls. 

B 67. 1'h relations o f th t•·•• P of the N wnrk )" tem in the New J rsey region, by Nel o n omtio Darton. 1 00. , 2 i'PB 10-t. Glnclntion of th e Y llow tone Va ll y north of the Park, by \\'nit r llltn·ey Weed. 1 93. 41 pp .. -1 pl8. 

B lOS . . \ g ologica l reronnni st~nee in central Washington, by Israel ook Ru~•ell. l 93. 10 pp., 12 pis. 

B 119. A geologicnl rcronnni once in northw t Wyoming, 1 y G orgc Homons Eldridge. 1 9.1. 72 pp., 4 pi . 

B 137. The geology of the Fort Hiley :\Jili1t1ry R ervoJion and vi cinity, Kansas, by Robert Hay. ~96. 35 pp., pis. 

B 141. The mora in s of th e Mi, url otenu and their ntt ndnnt deposits, b)· J ames Edwnrd Todd. 1 96. 7l pp., 21 pis. 

B 1 . The moraine of outhenstern omh Dtt.kota nnd their nttencinnt <1 po it.•, br J>tmes Ed wnrd Todd. 1 n9. 171 

pp., 27 pl ~. 

Blo9. Th g logy r 'n. t rnB ·rkshire ounty, tl."SachusetL~. byll. K.Eme .on. 1 99. J:l9 pp., 9 pls. 

B Hl-'i. ontributious to Lh geology of Maine, by Henry . . Will it1ms nnd U rbert E. r g ry. 1900. 212 pp., 14 pis. 

II' 70. Geolog y nod wat r resourc . of the l'tllri ck nnd .o hen llole qnndrangl s in en tern \\'yoming nnrl western 

N bra ·ka, by Georg I. Ad oms. 1902. 00 pp .. ll pis. 

B 199. Geology and wut er rc.•our s of th Sunkc Hh·cr PIHins of Jduho, by lsrnel . Hu ·ell. 1902. 192 pp., 2-5 pls. 

pp 1. Prcliminory report on the K tchiknn mining distric t, AIIL a, with nn introductorr :ketch oi the geology of 

southeastern Alnsko , by Alft·ed Hul c Brooks. 1902. 120 1 p .. 2 pls. 

PP 2. Rcconnai ance of tJ1c northwe:tern porti n of ewnr I Pen in ula, A Itt kH, by A. J. oilier. 1902. 70 pp. , It pis. 

pp 3. Tho geology on 11 clr graphy of Crater LnkeNntionnJ Park, by J. ·. Dill r aud li. B. PtLlton. 190'2. 167 pp .. t9 pls. 

9255-No. 3- 02- 12 
Il PUBLICATION OF UN[TED TATE GEOLOGICAL SURVEY. 

SERrE,' D1 PE'I'R CllAPnY AXD )111<~:1 ALOG Y. 

1. On hypeNthcnc-nnd ~itc and on lriclin ic p)'l'oxcno in nugilic rocks, by Whitmnn Cross, with t\ ~teo oglc>tl sketch of 

Bn!Jalt) P 11k•. Colomdo, by f:. . "mmons. 1 42 pp., 2 pis. · , 

. On >ccomhny enlargements f mineral frn.,me:1ts in cerlain ock~, by R. D. lt·,·ing nnd C. R. V11n !lise. 1 . 56 

pp., 6 pis. 

n 12. A ry ~tllogrnphic •tndy of th thinolite of Lnkc Lnh nt nn, by E. ·. Dnnu . 1 I. 3 1 pp., 3 pis. 

B n. On th e de,·clopment of c rystullizotion in the Igneous r cks o r Wu.'hoc, Xcvuda, with nol c. on th g ology of th e 

district, by Arnold Unguc a nd J. 1'. Jclrlings. 1 c. •1·1 pp. 

B 20. Contributions to the minc rulogy of tho Rocky )[ountuins, by Wl1itmnn ro:s nnd W. 1•'. Hill brnn I. 1 5. I l<l pp. , 

1 pl. 

B 28. The g>tbbros an l ilssocitLtcd horn I Iond o r ks occurring in Lhc ncig hborh o<l f Bultimor , Maryland , by G. ll . 

Willinm. . 1 . 7 pp., 4 pl•. 

B 38. T'erid otit or Elliott County, Kentucky, by J . .. Dill r. 1. 7. 31 pp., 1 pl. 

J3 59. The g>lbbros and liS' ocintcd rocks in Dclnwarc, by F. D. Cheste r. .I 90. 45 pp., 1 pl. 

B 61. Contribution to the minemlogy of th Pncific c liSt, by W. H. ~~ I ville an I Wnld mar Lind •ren. 1 90. 40 pp., 

3 pis. 

B 62. Tho green tone- chist areas or the >rcnominec and )!a rqnetto regions f )fiehiga n; n contri bution to tho subjc 1 o r 

dynamic metamorphism in e ruptive rock·, by G. H . \\'illin.ms; with io lroducti n by R. D. ln•iug. 1 90. 24 1 pp., 

16 pi~. 

B 66. On >tgroup or ,·oJcaoie rocks from the '1' wnn Mountnins, N w M xico, nn I on I he occurr nee f primary quartz 

in certa in bnsnlts, by J. !'. Iddings. 1 90. 3 1 pp. 

B 74 . The minerals or Korth Carolinn, by F. A. l nih. J 91. 119 pp. 

B 79. A late Yolcanic e ruption in northern •tliforni•t and its 1 eculi ur ln,·n, by .T . • ·.Dill r. 1 91. 33 pp., 17 pis. 

B 89. ome lavtt flow· or the w ·te rn ·lope of the ierrn NcntcltL, nlifornin, by F. L. Ransom . 1 9 . 74 pp., 11 pis. 

B 107. The trap dike · or the I..nke Champlain r gion, by .J. F. K mp nnd . F. ~ra ers. 1 93. 62 pp., •I pis. 

B 109. The e ruptiYe nncl seclimentary rocks on Pigeon l' in t, Minnesota, Hncl th ir contnct phcnomenu, by W. S. Buyl y. 

1 . 121 I p., 16 1 I.. 

B 126. A mineralogical lexicon of Fronk lin, n amp:hire, >Lnd Hampden conn lie,, MH. ;;nchiL' u~. by B. K. Emerson . 1895. 

180 pp., 1 pl. 

B 136. Volcanic rocks or ."outh Mountain, r nn ·ylvnnin, br Fl en~e 13uscom. 1 96. 124 pp. , 2J pi•. 

B 150. The educational . rie o! rock specimens collected and eli 'lribut d by th nit d 'tate Geological 'urv y, by 

J . . Dill er. 1 ~. 400 pp., 47 pi . 

B 157. The gnei ·es, gabbro-schists, and associated rocks of soutbwe ·te rn ~liHn e·oto, by W. Hull. 1 '99. 100 pp. , 

27 pis. 

PP 3. Geology and petrography or Cmt r Lnkc :fationul Ptlrk, by .J . • Dill er a nd H. B. P•llton. 1902. 167 1 p., 19 pis. 

Corre-1 ondence shouill be addressed toThe Duu:<.'TOH, 

UNITED STATES GEOLOG I AL • lli"EY, 

w A.SlllNGTON, D. c. 

November, 1902 • 

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