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ADVERTISEMENT. 

The publications of the United States Geological Survey are iasued in accot.dance with the sintute, 

approved l!arch 3, 1S79, which declares that-

• • The publications of the Geological Survey shall consist of the annual report of operations, geological and economic maps illustrating the x·esources an<l classifications of the lands, and reports upon 

general an<l economic geology and paleontology. The annual report of operations of the Geological Survey shall accompany the annual report of the Secretary of the Interior. All special memoirs 

H.ud repoxts of said Survey shall be issued in uniform quarto seriesif<leemed necessary by the Director, 

but otherwise in ordinary octavos. Three thousand copies of each shall be published for scientific 

exchange s and for sale at the price of publication; and all literary and cal'tographic materials received 

in exchange shall be the property of the Unite<l States and form a part of the library of the organization. And the money resulting from the sale of such publications shall be covered into the Treasury of the United States.'' 

ANNUAL REPORTS. 

From the above it will be seen that only the Annual Reports, which form parts of the reports of the 

Secretary of the Interior and are printe<l as executive documents, are available for gratuitous distribution. .A. number of these are furnished the Survey for its exchange list, but the bulk of them are 

supplied directly, through the document rooms of Congress, to members of the Senate and House. 

Except, therefore, in those cases in which au extra number is supplied to this office by special r esolution, application must be made to members of Congress for the Annual Reports, as for all other exec· 

-:1tive documents. 

Of these annua.ls there have been already published : 

I. First Annual Report to the Ron. Carl Schurz, by Clarence King, so, Washington, lSSO, 79 pp., 1 

map.-A preliminary report describing plan of organization a.nd publications. 

II. R eport of the Director of the United States Geological Survey for 18SO-'S1, by J. vV. Powell, S0 , 

Washington, 1S82, lv, 5S8 pp., 61 plates, 1 map. 

CONTENTS. 

Report of the Director, pp. i-lv, plates 1-7. 

Administrative Reports by Heads of Divisions, pp. 1-46, plates S and 9. 

The Physical Geology of the Grand Calion District, by Capt. C. E. Dutton, pp. 47-166, plates 

10-36. 

Contributions to the History of Lake Bonneville, lly G. K. Gilbert, Jlp. 167-200, plates 37-43. 

Abstract of Report on the Geology and Mining Industry of L eadville, Colorado, by S . F. 

_ Emmons, pp. 201-290, plates 44 and 45 • 

.A. Summary of tbe Geology of the Comstock Lode and the Washoe District, by George F. 

Becker, pp. 291-330, plates 46 and 47. 

Production of Precious Metals in the United States, by Clarence Kin~r, pp. 331-401, plates 4S-53 • 

.A. New Method of Measuring Heights by means of the Barometer, by G. K. Gilbert, pp. 403-565, 

plates 54-61. 

Index, pp. 567-58S. 

The Third .A.nn~nl Report is now in press. 

MONOGRAPHS. 

The Monographs of the Survey nre printed for the Survey alone, and can be distributed by it only 

through a fair exchange for.books needed in its libmry, or through t.he sale of those copies over and 

above the number needed for such exchange. They are not for gratuitous distribution. 

So far as already determined npon, the list of these monographs is as follows: 

I. The Precious Metals, by Clarence King. In preparation. 

II. Tertiary History of the Grand Calion District, with atlas, by Capt. C. E. Dutton. Published. 

(1) 
2 BULLETIK UNITED STATES GEOLOGICAL SURVEY. 

HI. Geology of the Comstock Lode and Washoe Distrbt., with atlas, by George F. Becker. In press. · 

IV. Comstock Mining and Miners, by Eliot Lord. In press. 

V. Copper Rocks of Lake Superior and their continuation through Minnesota, by Professor R. D. 

Irving. In press. 

VI. Older Mesozoic Flora of Virginia, by Prof. Wm. M. Fontaine. In press. 

Geology and Mining Industry of Leadville, with a+.las, by S. F. Emmons. In preparation. 

Geology of the Eureka Mining District, Nevada, with atlas, by Arnold Hague. In preparation. 

Coal of the United States, by Prof. R. Pumpelly: In preparation. 

Iron in the United States, by Prof. R. Pumpelly. In preparation. 

Lesser Mbtals and General Mining Resources, by Prof. R. Pumpelly. In prepa.mtion. 

Lake Bonneville, by G. K. Gilbert. In preparation. 

Dinocerata. A monograph on an oxtiuct order of Ungulates, by Prof. 0. C. Mar~h. In press. 

Sauropoda, by Prof. 0. C. Marsh. In preparation. 

Stegosauria, by Prof. 0. C. Marsh. In preparation. 

Of these monographs, No. II is published, viz: 

II. Tertiary History of the Grand Canon District, with atlas, by C. E. Dutton, Ca.pt. U.S. A., 1882, 

40, 264 pp., 42 plates, and atlas of 26 double sheets folio. Price $10.12. 

Nos. III, IV, V, and VI are in press and will appear in quick succession. The others, to which 

numbers are not assigned, are in preparation. 

BULLETINS. 

In its Bulletins the Survey will print such papers r elating to the general purpose of its work n.s do 

not properly come under the heads of ANNUAL REPORTS or MONOGRAPHS. 

The Bulletins will each contain but one paper, and be complete in itself. They will, however, be 

numbered in a continuous series, and will in time be united into vo1umes of conveni ent size. To fa.cilitate this each Bulletin will have two paginations, one proper to itself at the top, and at the bottom, one 

which b elongs to it in the volume. 

Of this series of Bulletins this paper forms No.1, and is also the first part of Volume I. 

Its price is t!ln cents. 

Correspondence relating to the publications of the Survey, and all remitta.nces, shouid be addressed 

t.o the 

DIRECTOR OF THE UNITED STATES GEOLOGICAL SURVEY, 

Washington, D. a. 

WASHINGTON, D. C., February 24, 1883. 

(2) 

/ 
,. 

DEP Al~T.i\'IENT OF T HE INTERIOR · 

BULLETIN 

OF TilE 

UNITED S T ATES 

GEOLOGICAL SURVEY 

No .~ 

W ASHI:NGTON 

GOVERNMENT PRI NT I NG OFFI C E 

1883 



UNITED STATES GEOLOGICAL VEY 

J . W. POWELL DIRECTOR 

ON 

HYPERSTHENE-ANDE ITE 

A:SD O:S 

TRICLINIO PYROXENE IN AUGITIO ROCKS 

BY 

WHITl\1AN ORO 

WITII A 

GEOLOGICAL SKETCH OF BUFFALO PEAK COLORADO 

BY 

',F. E~1MO~S 

GEOLOGIST ~ Cn ARGE OF ROt:KY OU TAl~ DIVISION 

W .A.SHINGTON 

GOVERNMEN'J.' PRINTING OFPI OE 

1883 

LETTER OF TRANSMITTAL. 

UNITED STAT. GEOLOGICAL SURVEY, 

DIVISION OF 1'HE ROCKY MOUNTAINS, 

])enver, Colo., October l , 1882. 

Sm: I have the honor to transmit herewith a paper by Mr. Whitman 

Cross on Hypersthene-Andesite, with a brief sketch by myself of the 

geology of Buffalo Peaks. 

The material from which it has been prepared was obtained during 

the geological study of the Leadville region, and would naturally ha•e 

been included in the monograph on that district but for the followiug 

reason: The andesites from Buffil>lo Peaks, which, at first glance, appeared to be most characteristic augite-andesites, were found by Mr. 

Cross on careful examination to differ essentially from the normal order 

as commonly described. In tracing out the relations of these rocks to 

the closely·allied so-called augite-andesites, Mr. Cross has obtained results which, if substantiated, give to these investlga.tions a mnch more 

general than local character, and make them of value to lithologists in 

general; so that it seems desirable that they should be published .by 

themscl,es in the form of a special paper. . ' 

Very respectfully, your obedient servant, ~ 

Hon. J. W. POWELL, 

S. F. EMMONS, 

Geologist in Oharge. 

])ir~ctor United States Geological Survey. 

(7-8) 
' 
• 

CONTENTS. 

LETTER OF TRANSMITTAL .........••...•.....•••••• -.. --...•••.........•••.. 

INTRODUC'I9RY GEOLOGICAL SKETCH OF BUFFALO AKS, nY S. F. EMMONS ...• 

ON RYI'ImtiTUE:-IE·ANDESITE AND ON TRICLINIC PYROXJ"~"E IN AUGITIC ROCKS, 

uy WHITMA.t.~ Cnoss .•••..•..•.......................•. - .•. - .. -•••. •••• -.. -

CHAPTER I.-Hypersthene-andesite from Buffalo Peaks, Colorado ..••••....... 

Description of rock •.•......•....•..•••••• .•.•••...•.................. 

Trielinie pyroxene in other rocks ...... . ................... ......... . 

Chemica.! composition of the rock ..•.....••.. .•.••..•.•..•...•. .......• 

Isolation and analysis of hypersthene .••••. . .••....•••. ••.••. ....••... ~ 

CHAPTER H.-Rhombic pyroxene in other andesites •••••... ..•. ....•• .......• 

Previous observations of rhombic pyroxene in augite-andesites ... •••• ••• 

Rhombic pyroxene in diabasic rocks ............ ................ . 

Rhombic pyroxene in hornblende-andesite ...................... . 

Cl assification of andcsitic rocks .................. ...... ............ . .. . 

Results .... .... .......... ............... . ......... .............. ..... . 

ILLUSTRATIONS. 

Page. 

7 

11 

19 

19 

19 

23 

2!i 

2G 

31 

33 

35 

36 

36 

38 

PLATE I.-Buffalo Peaks, Mosquito Range .... . ............... ........ . . ---· · 5 

PLATE II.-M1cro-eections of crystals .......... .... "' ...... .......... -·. ••• • 39 

(9-10) 

• 
• 

• 
INTRODUCTORY GEOLOGICAL SKETCH OF BUFFALO 

PEAKS, MOSQUITO RANGE, COLORADO. 

BY S. F. EMMONS. 

Doring the summer of 1880, a little over two months' field-wol'k was 

devoted by the part.y under my charge to a geological study of a portion of the Mo quito or Park Range, as an essential preparation for the 

investigation of tho remarkable ore deposits of the Leadville region. 

Tl!e area coYered by tho geological map prepared at tl!is time, wl!iclt 

included a length of about 20 miles along the cr<;>Elt, compri ed not only 

it mo t elevated portion, but also, with a single exception, the most 

interesting part of the range from a geological stand-point. Tills exception was found in the Buffalo Peaks, a double-pointed. mountain 

ma s ri ingabont l,OOO or 1,500 feet above the main crest, some lOmiles 

south of Weston's Pass, at the southern limits of our map. Two days 

were devoted ~o a !Jasty examination of these interesting peaks; but, 

although as many weeks might have profitably been employed in their 

stndy, for the reason that the geological phenomena here exhibited hacl 

no apparent connection with the ore deposits at Leadville, it was not 

eonsidered advisable at the time to devote any more of the brief working season of this elevated region to an extraneous study, however iuterestin~. Inasmuch, however, as the microscopical investigations of 

the specimen collected at that time, made by Assistant Geologist .Mr. 

Whitman Cross, have led to the discovery of hitherto unrecognized 

characteristics in an important g roup of Tertiary volcanic rocks, which 

is set forth in the following pages, it may not be inappropriate to preface his paper "ith a brief geological sketch of the structure of these 

peak , and of their relation to the rest of the range. 

The 1\Io quito Range north of ·weston's Pass is ma<le up of Palreozoic beds about 4,500 feet in thickness, extending from the Cambrian to 

tlJe Upper Carboniferous, with intercalated sheets or intrusive masses of 

•arions quartz porphyries and porpbyrites, resting on Arcbreun gran· 

ite aud gneiss. The elevation of the range, which took place at tile 

close of the Cretaceous period, was accompanied by the compression of 

thes~ beds into a 8eries of sharp folds, characterized by a steep side to 

the west, or towards the Archrean isli10d, round which the sediments 

were originally deposited, and by numerous longitudinal faults, with . (11) 
12 BUFFALO PEAKS. fBull.l. 

an upthrow to the east, more or less parallel to the axes of the folds, 

with which; in general, they are intimately connected. 

Towards the south this structure becomes gradually simplified, and 

the porphyry bodies thin out. At Weston's Pass, already, in place of 

the complicated system of faults and folds observed in the latitude of 

Leadville, two great anticlinal and synclinal folds are found, whose 

axes have the direction of N. 300 W., and whose eastern member has 

been raised by displacement along a fault plane ha-ving about the same 

direction. One of these folds occupies the main crest of the range, 

and its corresponding fault runs along the trough of the synclinal on 

the west, by whose movement the Archman granite is raised on the 

crest of the range about 2,000 feet a~ove its corresponding position 

under the Palmozoic beds which form the surface at the pass itself. 

The thickness of the interbedded porphyry sheet, which opposite Leadville reaches over 1,000 feet, has here diminished to a little over 20 feet. 

The other fold forms a secondary elevation, called Sheep Ridge, on 

the foot-hills, five miles east of the crest. Here the fault line corresponds 

very nearly with the axis of the anticlinal fold, which is also that of 

the ridge, the movement of displacement gradually decreasing in a 

southerly direction, until the fault ridge becomes simply the elevation 

of an anticlinal fold. About five miles farther south, at the junction of' 

the Little Platte, which from Weston's Pass flows southeast along the 

trough of the synclinal, and of Rough-and-Tumbling Creek, which drains 

the north slope of Buffalo Peaks, not only have the two great faults disappeared, but the two systems of anticlinal folds are merged into a 

single monoclinal. · 

Topography is here in singular sympathy with geological struct-

. ure. Both the main crest and the secondary ridge to the east have the 

same general direction, with the strike of the geological formations, 

while the average direction of the topographical crest of the range, as 

a whole, is more nearly north and south, and its structure consequently 

that of a series of ridges en echelon. Sheep Ridge on the east disap- · 

pears completely under the plain before the -valley of the Little Platte 

is reached, and is succeeded by an isolated butte called Black Bill, 

formed by a massive outburst of crystalline rhyolite, breaking through 

and spreading out over the upturned edges of the Upper Coal Measure formation. The main ridge, which forms the eastern wall of Weston's Pass, descends rapidly to the south, reaching the level of the 

valley as the Little Platte bends east to flow out into the plains of the 

South Park, just abo-ve its junction with Rough-and-Tumbling Creek. 

Between these two creeks and near their junction is a series of low 

ridges formed by strata standing at a great Yariety of angles and with 

varying directions of strike, which show the effect of the merging of the 

double system of folds to the north into the simple monoclinal structure 

which prevails to the south. 

The topographical divide of the range therefore leaves the main crest 

(12) 
EMMONS.) STRUCTURE OF THE MO~QUITO RANGE: 13 

at Weston'!'! Pass, and crosses to a second ridge, which overlaps it, on the 

west of the pass. Stretching southeastward in the direction of the strike, 

it continues "ith apparent regularity as far as the Trout Creek Pass, 

about 20 miles clistant along the crest of tl1e range. The structure of 

this portion of the range, as determined in our hasty \isit, seems quite 

simple. On the west, towards the Arkansas Valley, it pt•esents steep 

precipitous slopes of .A.rchrean granite. The crest of the higher portion of the 1'idge is covered by a thin shell of easterly-<lippiug Cambrian 

quartzite whose average t.hickness in this region is about 150 to 200 

feet. Resting conformably on this is the White or Silurian Limestone, 

of about equal thickness, succeed¢ by tho. J-'ower Carbouif'erous or 

Blne Limestoue, :tlso about 200 feet in thickness; tlH:lll 2,000 to 2,500 

feet of silicious be<ls, wlticiJ h ave· been designated the Weber grits; aJHl 

a long the extt·eme eastern flanks of the range t he Upper Uoal Measure 

be<ls, wiJich consist partly of limestone and partly of coarse reddish 

sandstone. In the plains along the eastern foot of tlJo range are found 

occasional ridges of the red sandstonPs and shales of the Trias, from 

which it is probable that the salt of the salt springs ea t of Buffalo 

P eaks has been derived. 

Midway in this monoclina.l ridge, and resting on the upturned edges 

of the strata, <~re tiJe horizontal beds of-andesitic lavas which form the 

Buftil.lo Peaks. Their western base rests on granite, immediately under 

the quartzite, while their eastern flows, wllose limits were not ascertA~incll, probably extend well out over the Upper Coal :Ucasnre formation. The direction of strike of the sedimentary beds, on the north sirle 

at least 1 seemS tO IJave been but little affected l.Jy this extt·usion of VOl· 

canic material; but in immediate contact with the lava,. as will be shown 

htter, they have l.Jeen cousitlerably metamorphosed. 

The Buflil.lo Peaks form au extremely pictmesque monntain mass, 

whose bigiJest point rises to an elevation of 13,541 feet above sea-level, 

or about 4,000 feet above the adjacent valleys. It consists of a uarrow 

curving ridge forming about one.thir<l of a circle, its concave side toward tho nortll, with a culminating point at either extremity of the arc, 

the connecting saddle being about 500 feet below their summits. From 

the northeast b~se of the eastern peak spreads a broad, flat, massi\'e 

siJoulder, wiJo earea is cou irlerably greater than that of tho main peaks. 

Between tiJe two peaks lies a semi-circular amphitiJeatre about 2,0u0 feet 

deep, in which the appropriately named Iwugh-aud-Tumbliug Creek 

t.'tkes its rise, and fiows fhst uorthwa.r<l, then eastwrml to its junction 

with the Little Platte. The upper 500 feet of the two main peaks is 

formed of hornblende.audesite of decidedly traciJyt.ic llabit. Its matt·ix 

is of a browuish.gray color, with small crystals of whi te feldspar and frequent needles of black llornblende. In it columnar structure is very 

well <levelope<l, especially on the connecting ridge between the two 

peaks, where t~ columns are often only a few iuches in diameter. At 

this point, rounded ii'agments of Archmau rocks included i11 the au<lc-

(13) 
14 BUFFALO PEAKS. [BuU.l. 

site are of frequent · occurrence. · ~here is also a very considerable development ofhyalite on the weathered surface of the rocks, and fulgurite 

is found at the summit of the higher or western peak, lining small holes 

made by the electric fluid. 

The base of the hornblende-andesite is extremely well defined, as 

shown in the frontispiece, by a horizontal line at about the level of 

the saddle connecting the two main peaks. Below this, as well as 

could be seen on the walls of the amphitheatre where they were sufficiently steep not to be obscured. by debris, the mass of the mountain 

seems to be made up of tufas and of half-glassy modifications, which 

are also horizontally bedded, con¥>rmable with the base line of the 

hornblende-andesite. A section was made down the steep spur extending from the north base of the eastern peak into the amphitheatre, 

giving a freely estimated thickness of 1,000 to 1,500 feet of these tufa~ 

ceous varieties. SECTION. 

1. 200-500 feet.-Hornblende-andesite. 

2. 5o feet.-Semi-vitreous tufa of bright red color, with streaks of black and reddish 

glass running through it, and containing crystals of basic minerals and of 

feldspar, with innumerable small inclosed fragments of lavas and other rocks 

not always determinable. 

3. 100 feet.-Beds of similar material, rather black in color. Among inclosed fragments rounded masses of granite, up to 6 feet in diameter, are frequent. 

Through the mass are thin seams or beds of black glass of a perlitic structure, like an obsidian, with plentiful small fragments of feldspar scattered 

through the mass. . 

4. 100 feet.-White and lilac colored porous tufa, with fragments of light-colored 

tracbytic rock, rich in smoJry quartz (dacite or rhyolite'). 

5. 200 feet.-Tuface~us breccia, with boulders of black, vitreous-looking hyperstheneandesite. ' 

6. 5 feet.-Bed of dacite (rhyolite?)."' 

7. 50 feet.-Light-colored tufa with fragments of dacit,e (rhyolite f). 

8. 500-700 feet.-Space somewhat cov .. ered, mostly of tufa, inclosing fragments of 

a great variety of rocks. 

The next outcrop below the base of the spur was found to be limestone. and shales, probably belonging· to the Weber grits formation, dipping to the northeast at an angle of about 45°, and having the re6-;..tlar · 

strike of the sedimentary rocks of the region. Within these tufa beds, 

and weathered out on their surface, were found an immense number of 

*The "rock described here as dacite (rhyolite ?) is one which, from the specimens 

at hand, it has been impossible to assign definitely to either of these two classes. 

Macroscopically it resembles the rhyolites, having large smoky quartz and glassylooking feldspars in a lilac-colored matrix, and possessing a very decided trachytio 

habit. Microscopical examination fails to determine definitely whether the one specimen in the collection contains more orthoclase or plagioclase feldspar. A partial chemical analysis is equally unsatisfactory, giving silica, 66.500; potash, 2.567; soda, 

3.868. It is identical with a rock found breaking through the granite, near the town 

of Granite, in the Arkansas Valley, west of the Buffalo Peaks. A further field examination will be required to satisfacto:rily determine the character and relations of 

t.his rock. 

(14) 
l!l010S8.) THE SECTION AT BUFFALO PEAKS. 15 

more or iess rounded fragments of included rocks, consisting mainly of 

granite and various lavas; the latter of which, as far as examined by 

~ir. Cross, ha.,·e proved to be of the same character as the northeastern 

shoulder, i. e., hypersthene-andesite. 

The rock of t.he easteru sbonlder, as far as examined, is a dark, 

nearly black, compact, semi· vitreous rock of conchoidal fracture, which 

in the field was determined at once as an augite-andesite. The average 

level of this eastern spur is some 700 or 800 feet lower tllan tllat of tho 

summit of tho peaks. As far as our observation extended, this rock was 

not found in mass in direct connection with the hornblende·andesite. 

At the northeast base of the eastern peak, about midway between 

well-defined outcrops of the two rocks, a German miner had sunk a 

shaft on the fiat surface of the ridge, in an iron·stained, clayey material, 

undoubtedly tho result of decomposition of the lava, in which be found 

>cry large, irregular masses of milk-white, common opal. Some of these 

masses reached several feet in diameter, and when broken open it was 

generally found that their centre consisted of opaque, flint-like chalcedony; showing that in this case the opal had probably re olted from the 

hydration of chalcedony concretions within the rna s of the rock. It 

was also obscned that while the internal kernel of flint readily gave 

sparks when struck with steel, the exterior opaline portion was not of 

sufficient hardness to do this. A chemical examination was made of 

the flint-like kernel and of the white opaline alteration product, with 

the following result: 

Flint. Oplll. 

SpeciJlo gravity • . . • . • . •• . • . . . . . . . . . . . 2. 670 2. 0~3 

llardneaa . • • • . . . • • . • • . . . . . • . . . . . . • . • . . 6. 5. 5 

Lou by Ignition (water)............ . . L ~3 2. 584 

Inaoloble (In eauatlo potash) silica.... , 32. 430 0. 710 

Soluble eUler. • • • ••• •••••• •••• •• • . ••••. Ga. 727 98.700 

100. 000 100.000 

F rom which it would seem that the change to the opaline form is 

not simply the result of hydration, since the increa e in water in the 

:tatter case i onls 0.7-H, or a little over a third more than in the original form of the secretion, bot that this must have been accompanied 

by some molecular change, by which the percentage of soluble silica. 

has become nearly one-half greater. 

The outcrops of the upturned sedimentary beds conld be traced up 

to the very entrance of the amphitheatre; the Weber shales, as already 

mentioned, had been already observecl at tho · base of tho eastern 

peak; tho Lower Quartzites resting on the granite form the main crest of 

t he range immediately north of the western peak, while at the northeast base of this peak, at the entrance to the amphitheatre, there was 

(15) 
16 BUFFALO PEAKS. [BuU.l. 

a cropping of white and blue silicified limestone, showing in a. very interesting manner a relic of the solfata.ric action which probably succeeded the 

eruption of the laYas. Here the bedding is distinctly seen; the color 

of tho limestone, its granular structure and characteristic veining are 

still pre orved; but the whole mass is completely transformed into silica, and the surfaces frequently coated with a thin white opaline deposit. 

Chemical tests of three specimens brought from the e outcrops, one 

white or drnb, the other two blue limestone, 1:1howcd the following contents in silica: 

Per oont. 

White llmeijtone ..... ...••......... ........ .. .. ....•...... .....•... .. .•.... .. 97.1 

Bluish limestoue ......... . ................. .................................. !J7. 7 

Darker limestone ............ ................................ . ............... . 78. 9 

with an11'apparently more than normal proportion of manganese, especially in the darker colored specimen. 

The southern slopes of the peak were not examined, but from the 

summit outcrops of the upturned sedimentary beds could be seen 

continuing on southward beyond the base of the peak, npparently in a. 

direct line with those observetl on the north. Tho very centre of the 

amphitheatre was al o not visited, as the soft slopes re ulting from the 

decomposition of the tufa. beds promised but few outcrops. 

Two important questions present themselves in the consideration of 

tbe structure of this interesting mass; neither of which, unfortunately, 

can be consid~rod as definitely decided by the hasty observations made 

during tbis visit: 

First. Are tbc peaks the relics of an old volcanic crated 

Second. Was the hornblende- or the hypersthene-andesite tho earlier 

:fiow t 

To tho first question tho circular form of t.bc main ridge, and its 

bedded structure, seem at first glance to give a decidedly favorable 

answer. More mature consideration shows that tbe pre ent form was 

mainly duo to glacial and post-glacial erosion, whose work in this region 

has been on such a stupendous scale that evidently the present form of 

the peaks affords little guide as to the original condition of the mass. 

Had the present semi-circular ridge once formed part of the crater, we 

should expect to fintl some relic of tho re t of the circle resting on 

the ridges to the north; but with the exception of tho northeast 

shoulder, which co~ists of a distinct rock, and which is e\idently also 

the result of a distinct flow, no lavas were found north of the entrance 

to the amphitheatre . 

.As regards the relative ages of the two varieties of andesite, it is to 

be observed, first, that the bornbleude-andesito is the higher of the bedded series; and, second, that from the tufaceous beds no fragments of 

t.he hornblende-andesite were obtained; while those of hyperstheneandesite were of very frequent occurrence. On tho other band, the :fiat 

eastern shoulder, which is probably formed of hypersthene-andesite, re-

(16) 
1:)01 ~! ) TilE AGE OF THE A:\"DESITE . 17 

$<:'mble iu its form the lateral flows which come from tlH' side of already 

built-up volcanoes; and as a general rnle th{' more ba8ic augite aud · 

sites have been found to be younger than the horn blcudic varieties. ln 

the case of lava:>, superposition is uy no means ecc:-~sar ily a, proof ofla ter 

origin, inasmuch as the later flows oft.en force themselves undet' tho,·e 

already existing. Still,' in the pre ent ca e, it must be aclmowleclgetl 

th;tt tllo evidence, as far as obtained, is in fa \·or of tlle earlier origin of 

the byperstbene-an<le itc. 

A third point of interest for future investigation ~ the determination 

of the trne character a.ml relatious of the dacite (rhyolite 1) rocks. 

The fttct that in tho present stage of microscopical li log~· tho oltl 

test of tbe ab enoo of striation lines visible under the micro cope is no 

longer sufficiently conclusive to determine a feldspar as orthocl:vtic, 

reudt>rs of doubtfnl \'alue the earlier classilication of many rock al5 

tt'acbytic or ande. itic. :Uauy facts already obsen ·e•l b~" u Suf!g-e, t a. 

doubt whether von Ricllthofen's classifimttion of ,·olcanic rocks will uo 

timntl to hold good everywhere in Oolot·ado, and even that many modifications of the 1·elations of tlte oldet' ern pti \"e ro ~;, as well a of tho:-~o 

of '£ortiary age, ma~· be round necessary. The Held of work i · grea.r, 

anti will iu,olve longantllnboriousstndies beforcdcfiuith·e rcsnltscan b 

obtained. Io the western portion of the CorcliUcran s~· tem Tet'ti:H'.Y 

volcanic rocks and rHcent lavas are in vast prepoudet·aucc, and the oldN 

ernptiYes have been found tbns far in but few points. In 'olor:ttlo, 

however, while the tlcvclopmeutof Tertiar.r ernpth·e rocks is considerable, it seems probable that a vet·y large proportion of the eruptiYC r·ock" 

will prO\'C to belong to those generally classed as older, horn their 

lithological chararctcriRtics alone; of t.bese, howc,·er, tllo most witl<•ly 

•leveloped class mny douht.II'SR prO\·e to be Pof>t,-Orctnccous, an<.l of tltoso 

which belong lithologically to t he cla.·s of Tertiar·.r crupti\'CS or Yolcanics, tbm·e are many wlw e period of eruptiou cun be but little later 

than this period. 

(17) 

Bull. 1-2 

ON HYPERSTHENE-ANDESlTE AND ON TRICLINIC 

PYROXENE IN AUGITIC ROCKS. 

BY WHITJ\f.A.N CROSS. 

CHAPTER I. 

HYPERSTHENE-ANDESITE FROM BUFF A.LO PEAKS, COLO· 

RADO. 

The microscopical and chemical investigation of certain andesites from 

the Buffalo .Peaks in the J\fosquito Range, Colorado, having proved conclusively that a rhoml>ic pyroxene is, after plagioclase, the most essential cou titu~ut, the writer was leu to examiue carefully all similar rocks 

at bis comma.nd. As the results attained are wide-reaching, and affect 

ma.n.v well-known European rocks, the obsP.rvatious made on the Bnfiillo 

Peaks rock will be given in detail in Ubapter I; the results of t he com. 

parative study ar·e embodied in Chapter II. 

The "Introductory Geological Sketch" l>y Mr. S. F. Emmons renders a.ny ful'ther description of the Bufl'alo Peaks unnecessary; all reference to topographical or structural detail will be found sufficiently 

explained iu that sketch. 

DESCRIPTiON 0}1' ROCK. 

Those rocks which are to be specially considered in the following 

pages occur principally as included fragments in the tufa beds, and 

were found in place only on the shoulder of the main peak wllich projects to the northeast. 

This latter rock is compact, dark or almost black in color, showing 

minute glassy feldspars, which, b,v reason of their transparency, seem 

(lark also. A careful examinMion shows a number of small, dark-green 

grains au(l prisms, which arc unlloul>tedly pyroxene, aud glistening ore 

particles. In the ft·esh state the base in which these minerals lie has 

a vitreous lustre. 

The fragments found in the tufa vary in outward appearance. Part 

of them a.re as dark and compact as the one just described, while others 

are lighter colored, with mor~ distinct crystals of feldspar and a some-

(19) 
20 HYPERSTHENE-ANDESITE. [BuU.l. 

what poron ground mass. In the d.'l>rkt>r ones, the feldspars are in part 

of a clear .YCllowi h tinge, producing a \"Cry cce 1tin~ re emblance to 

th~:~ partiaHy uccomposoo olidue of ba altic rocks. 

·when exami ned nuder the microscope iu ordinary light, the e rocks 

seem to be t.Ypical augite-andesites of nry simple compo itiou; clear 

pl ag-iocl~o crystal , p,yroxeue in small cr)-stals and irregular grains, 

with magnetite and apatite, are the only minernl constituents to be 

recognized. 'l'hese larger individuals lie in a groundmass composed of 

tiJiu plates of plagioclase, light-green micr·olite of pyroxcm-', aud minute 

octalteclrons of magnetite, with a g lass basis between them, wiJicla is 

usually clear, though sometimes de,·itri !:ied b.Y ligllt-bmwnisiJ globu lites. 

In t.ho rock occurring in place, tho nlicroli tes arc nnnsuaHy large, while 

in the otlrcrs they sink to extraorclinarily miunte 11cetlles. 

PECULlATUl'lES OF 1'HE PYROXEN1~.-BX<\m iu ctl in pola.rized ligllt, 

none of Lho cloml'nts, except. the pyroxeuc, siJow noteworthy peculiarities. 

A stu<l_y of the p_yroxenic constituent force one to the conclu ' ion that a 

1·/wmbio mineral, pmbably hypersthene, iiJ lm·gely predominant, 1t'hile a great 

n1tmbcr, if not all of the remaining inclivillualo, 1IW1Jl be cowside1·ccl as triclinio il~ ory~> lallization. 

l'hi · conclusion is based on the following mict·oscopical and ciJemica.l 

iuve~ti~atio s: 

In tbc first phwc, on tcstiug under the micro cope, in pol:trizcd light, 

all tltc prismatic sections antl small prisms who ·o ,-crtical axis seemed 

to lie in the pia,ne of the thin section, with regard to tlJeir optical orientation, it was found tllat at least one-half, aucl generally a lllllCh larger 

JH'O[>Ortion, possessecl an axis of elasticity parallel to the vcrlical crystnllogl'uphic axis. Now, the only section of a mouoclinic mineral, in th e 

prisrnatie zone, which could act in tlJis ma nner, is pbinly th at parallel 

to the or·thopinacoid. .And any. one who has te ·teLl tho prismatic sections of augite or hornblende, ju slicles of mns ·ivo rocks, lmows how 

r•tt·ely a section can be found so neal'ly parallel to the ol'thopinacoid 

that. no tlcYiation of the direction of total extin ction fr·om the \'Ct·tical 

crystallogmplJic axis cau be detected. Tbe ju tifiable conclusion is 

ther·efore reached, that nearl.r all of the sections in que,;tion bcloug to 

a rhombic nliueral. 

In the next place, the st>ctions apparently cut perpentlicula.l'ly to 

tho nrtical axi present a nother rcrnarkahle deviation fL·om the rnle. 

While uch l'Ctions siJould give no data for tlJo · •paration of rhombic 

from monoclinic pyroxene, since in both the tlit·ections of oxtiuction coincicle with the diagonals of the prism, it is hero fouud that in only a 

llortion of tho scct.ious docs this r('lation actually exist, nntl, further, 

the 1111 mericn l ratio hetw·cen those cross-sections wi tit normn.l and tiJose 

witlJ abnormal optical relations is, i.n auy given slide, nearly eqnal to 

the ratio between those prismatic sectious showing the rhombic and 

'tho!'lo witb deviating optical orientation. It is at once suggested tliat 

the cross-sections sl10wiug normal optical action ooloug to t he same 

'(20) 
cnose.] DESCRIPTION OF PYROXF:NE. 21 

mineral which, in longitodiual sections, appear as rhombic, while tlle 

prismatic sections, which are seemingly normal a ugite, belong to the 

apparently triclinic mineral. 

The rhombic mineral as sbown by the chemical im' e tigations (p. 2!>) 

mr1 t be considered as hyper·stbene. Its pleochroism, t hongh mstinct, 

is by no rueans strong. A section nearly or quite at right a ugles to tho 

pri ·m has a light greenish-yeilow color, and the changes on e~o ing 

it t hrough 900 are too ~S li ht to be expressed. In prismatic section tho 

byperstl.l ene is pale-green in color when its vertica l a."':i i perpendiculnr to tho pl'incipal section of the nicol, and greenish-yellow wbcu tbel':le 

directions at·e lHH'allel. Iu tho latter position there _is so timt~s lt tiugo 

of brown. The other pyroxene is uot pleochroic to any noticeable <leg reo. 

It. i always of a pale-gr·e n color. 

The cro -secti ~ of hyper th ~ are very well defined. They show· 

the ciHtracteristic eight-sidecl figures of pyroxene, with a distinct prismatic clcaxage, a nd, quito snl>ordinate in some of tltc ectious, n cleavage p amllel to tho pinacoids. In most of the sections showing a rhombic chm-aclit'r, the pinacoiuul faces are predominant, tlle pl'isu t iutvly 

truncating tlle angles of tbe rectangle formed by tho former f<tces. 

'fil e ~~~ st c does not show the prismatic cleaval!o in longitudinal 

sections so plainly a the triclinic mineral. The iines are fiu cr, n ml cro~sti'ssnres are common. The t-erminations, too, are oftl'n qnite regulnr, 

being doubtle s eau e<l by domes. (See F ig. 9, P lato II.) It is in the 

small <:r.r ·tats especially tb[tt t he r egular form of a rltom l>ic mineral is 

most plain. In the dark and compact rocks thoro is lc s difl'c c' l>ct.we«'lt th ese two miuerals t han in t.lte lighter aud porous on<.'s. In the 

latter one tlntls some m·ystals of hypersthene, which are fi l.Jrons, with an 

iucipicnt decompo ition proceeding from the cross-fissures along the 

vertical <;le:wago planes. ( cc Fig. s, Plate II.) 

'l'R.lCLrNro P YR OXENE.-Those cross-sections, showing an anomalons 

po ·ition of tlte axes of elasticity, aro in many ways remarkal>h•. The 

outline arc similar to tho e of monoclinic augite, being eig"Llt-sitle<l tignrcs, witlt a. di tinct cleavage parallel to what runy be taken as the 

prism. Tbo deviation of the an gle of extinct.ion ft·om the norma.! ono 

for monoclinic minerals is 110t constant. Very many of t he crystn.ls a1·e 

apparent twins, and tho twinning plane l>i~ects tbe prism augle in all 

ol>sen·ed case . 

For convenience, it will be assumerl that this plano is the macropinacoicl, in accordance with the common law of augite. The di vergence of 

the direction of total extinction from this assumed mncrofliagonal is in 

most cases o to 25o, uut ca cs are not rare of its exceeding this aver' 

a.ge up to 330 30' as obsen retl maximum. It is more oft.en a bo,·e 250 

than below 200. It is not uncommon to find se,·eral a.nglcs of extinction ioditle t·en t portions of the same cross-section. Tbis will be best 

understood l>y a refe1·ence to the figures of Plate II. 

Plate JI.-Fig. 1 represents a section with partially regular outline, 

(21) 
22 HYPERSTHENE-ANDESITE. (Bull. I. 

and a cleavage most pronounced in two directions, cutting each other 

at an angle of 1)early 900, In ordinary light it seems like a simple section of pale augite. In polarized light it appears at first to be a trilling 

whose composition face is oo P oo. On determining the direction of total 

extincti6n, the (in figure) upper and lower portions are found to agree 

with an angle of 270 30' from the assumed macrodiagonal. The central 

portion, however, bas an angle of extincti8n of 100 30', cutting tb.e macrodiagonal in corresponding direction with the .preceding. Its relations to the other portions are, therefore, not thos~ of a plate in· true 

twinning position. Moreover, within the central portion, is a small 

irregular patch, wit.h cleav~tge parallel to that of the rest, having a third 

angle of extinction, viz, 60 30', and also in the same general direction. 

The phenomenon is hence to be regarded as an intergrowth of substances with common crystallographic, but differing optical orientation. 

The central portion shows brilliant colors of polarization in certain positions, while the other parts vary only in degrees of light and shade. 

In Fig. 2, the extinction of several parts is, as indicated, with angles . 

of UJO 30' and 37°. In this case, however, the parts are related as 

in a trilling crystal, the direction of extinction of the central portion 

cutting the macrodiagonal in the manner necessary had there been a 

revol11tion of 180° about the normal to the macropinacoid. The parts 

with extinction of 19° 30' polarize somewhat inore intensely tban th'e 

others. 

Fig. 3 shows a crystal 0.1Gmm in diameter, with twin structure, the 

angles of extinction being respectively 24° and 29o for the two halves. 

The former gh·es ·more brilliant colors in polarized light. 

Many small sections are very similar to Fig. 4, with about the same 

angle of extinction. Fig. 6 represents an apparent intergrowth of rhombic and triclinic pyroxene. The rhombic character is not demonstrable 

of course, but it seems most probable, as the inter growth of hypersthene 

and other pyroxene in prismatic sections is often visible. (See Fig. 

5.) The hypersthene polarizes brightly, while the other mineral neither 

gives distinct colors nor becomes very dark in any position between 

crossed nicols, so that its nature cannot be determined. 

Although measurements of crystal angles made on chan(le sections in 

a slide of a fine-gra:ined rock cannot, from the nature of the case, be 

accurate, an attempt was made to determine approximately the chief 

angles of the prismatic zone of this questionable mineral. As far as 

could.be judged the section of Fig. 1 was cut very nearly at right angles 

to the vertical axis, and its bounding planes . were sharply defined. 

The angle b of upper right-hand quadrant was first determined. The 

mean of seYeral measurements, taken in different ways, was almost 

exactly 1400, To obtain the ang-le a, a measurement from oo :P oo to the 

I) lane of intergrowth was made, as oo P oo was not well define·d; 13!.0 

was the result within a few minutes. Tbe angle of the two pinacoids 

:was next measured at 9!0 , which would be necessary for the two pre-

(22) 
CltOSS.] CRYSTAL ANGLES. 23 

ceding determinations. The angle a was determined a a mean of se\· 

eral trials at 1340 47', the prism angle between faces on right-hand of· 

section= 950 (nearly). 

A section of the prism of this mineral, at right-angles to the vertical 

axis, would therefore have the accompanying form: 

The figures of the plate will be seen to have a very similar form. If 

tlle sections Figs. 2 and 3 were of normal twins, according to a pinacoid face, thete shoultl be a re-entering angle visible, in case the above 

measurements are correct. On some of the sections ·een, this seemed 

to be actually the case, but they were too small and indistinct to admit 

of measurement. 

ln some of tbe cross-sections the cleavage is apparently bett.er developed parallel to one of the prismatic directions than to the other; for 

example, sec Fig. 1; but this difierence is very slight, and no weight 

cau be laid ou it. 

TIIIVLISIC Pl'ROXENE IN OTRllR ROCK~. 

The writer has noticed, and briefly described, an apparent tl'iclinic 

pyroxene in certain cr,ystalline schists in Brittany.

1 The pheuomenon 

was tllere less distinct than in the present case, and it, was then thought 

probable tllat it was au anomalous optical action of the monoclinic 

augite, tile cause of which was unknown. No twin structure or inter· 

growth was there noticed, and the divergence of the direction of extinc· 

tion from the normal one was even more variable than in the case in 

hand. The material, too, was less favorable for accurate observation, yet. 

the two iusronces are so similar that in all probability they are due to 

tlle same cause. 

A third occul'l'ence of this same phenomenon lias been ob crved by 

the writer in a feldspar basalt from Grand River, above the Hot Springs, 

Middle Park, Colorado . . Mr. S. F. Emmons, iu passing through the 

Park, collected specimens of several basalts, and one of them shows, 

under the mieroscope, a. pyroxene seeming in ordinary ligl1t typical 

of the normal tlng·ite of such rocks. It is not pleochroic to auy describable degree. Its cross-sections are eight·sidcd figures, with a strongly 

marl;:ed cleavage. Fig. 1, Plate II, represents a cross-section of a twiu 

1 W. Cross: "Stuclieu Hbur brotouische Gesteine." Min. und pet . .Mitthuilungeu. 

G. Tschermak, (Ncuo Folgo), III, 1). 396. 

(23) 
24 HYPERSTHENE-ANDESITE. [Bu/!.1. 

crystal ob:en ·ed in this basalt. Tile angles of oxtiuction for the two 

ha lves, l!)O arul ~~o from twinning plane, aro perhaps within the limits of pos il>le t>rror of ob ervation in a ection who •o exact position 

cannot be determined. All other cross-sectious show , imilar relations, 

hut t he angle of extinction \aries from 180 to 330 from a diagonal of 

tuo pri ·m. In longitudinal sections tue action is normf~l. 

'f bo Hu1ling of pyroxene with such abnormal optical properties in 

tlu·ce distinct roeks, from snell widely separated localities, I •tl naturally 

to the examination of the pyroxene in tlle common ~~ugitc rocks, ::;uch 

<\:i diabase, ba!:lalt, &c. Tue result of such examiuatiou is to s h'ow tlmt 

even in well-kuowu rocks a portion of tlle pyroxe ne does not exuibit. in 

]>Oinrizetllig h t tile properties required of a monoclinic mineml. In mauy 

cases, sections of the supposed augite, which, ti·orn all :wailable data, 

seemed to be cnt Yery nea.rl_y at right angles to t.he vertical axis of tbe 

crystal, were fouurl to act abnormally between m·o t;elluicols. A uumhct· of iust.auces are g-iven below, mainly from well-known European 

loca litie , whore this abnormal action wa noticed. Ju t>ach of tuese 

rock ' 7 at Ina tone st>ction of pyroxene was fnuntl, which, without examination in polarizPcl li~ht, would be coushleJ•ccl, as tlctet·naiued by tho 

following tc t , to be a typical cross-·ection of aug-ite. Iu th~ H rst place, 

if, iu a g-h·en rock. the p_noxene was fouud tc. po 8t>~S a prisn1atic deeloprueut, au eig-ht· 'i1lcd fig-ure with the proper ang-les was required. 

J>arallel to two of the ·e outlines there must. be a vcr.r distinct clea,age, 

tlle angles 1imned l>y cleavage plaue being- mea:Jnmble at Yery 11ear 

S'iQ aml U30, lly means of the micrometer Rcrcw, it conlcl be showli in 

eaeh case that the cleavage plane lay nearly Ol' quite parallel to the axis 

of the microscope. 

lu en.ch of tbe rocks mentioned below, n. s~ction of apparent augite, 

<l cterrnine1l, as abo,·e, to be nearly or quite perp endicular to the vertical cr~ stallogrn.p bi c axi ·,was found to oxtinguil;b light between cros·eu 

11 icols at a very tlecided angle from· the diagonals of tho prism. In all 

e:u~cs cited, the st>ction was clear, fresh, and free from all visible disturbing element . lu a few ca es, wbere the maxinuun of darkness was 

uot ,·cry di trnct, the iuterference cro of tue calcite pla.te an1l the most 

sensitive color protluccd by the quartz plato were used iu the determiIJa.tion. 

The in tances rt>ferred to are as follows: 

1. Diabase.-llkerutorf, near ~o en, Saxony. 

2. JJiabttse.-Nt>ttr Elbingerode, IIartz Motmtains, Germany. 

3 . .Diabttse.-Bnrg· in Nas an, Germany. 

4. Olivine-dirtbalie.-Bjorfvas, Dalarne, Sweden. 

5. Jfelaphyre.-St. ·wendel ou the Nahe, Get·many. 

6. Hornblend.e-nnifc.Yite.-Boh·ershalm, Sicbcugebir·gc, Germany. 

7. llornblende·a.ndc.tt'ite.-Jaknben, near 'l'ot~clleu , Bobe1n ia. 

8. "ilugitc-andesite."-.1\Iount Cotopaxi, Ecuador, Sout.h America. 

(24) 
CROS .] TRICLINIC PYROXENE. 

9. "Dolcritc."-Lowenburg, Siebengebirge, Germany. 

10. "Dolcrite."-The 1\Ici suer, IIcssen, Germany. 

11. Fclclspar-basalt.- Bihlstcin, Vogelsberg, Germa ny. 

U . Fcldspar-basalt.-IIolmestraud, Sweden. 

13. Nephelinite.-Meicbes, Yo e.l ~, Gcrmnny. 

14. Feldspm·-basalt lava.-)Ionnt 1Et:mt, eruption of 1537. 

1.3 . .Nepltelinc-basalt.-Rob cbitz, near Bilin, Bohemia. 

lG . .Nephcline-basalt.- IIercbcnberg, Laacher Sec, Get·many. 

17. L C1witc-basalt.-The Abtei, Laacher See, Germany. · 

1 . L cttcile-basalt.- Veitslwpf, Laacher See, Germany. 

1!). Leucitc-basalt.- :Nicderrnen<lig, Laacher See, Germany. 

0. H aiiyne-basalt.-Oranzahl, Saxony. 

2l. L euc'ite lava.-Mount Vesu>ins, old eruption. 

25 

Iu >ery many other ca es the same bcl.tavior was noticed, bnt les decillculy. Especially in comparison with t he hornblende of diorite, porphyrite, &c., is the abnormal l.Johavior of e noticeable. 

So far a is known to the writer, this abnormal action of uppo cd 

aug-ite ha JlO>er been dwelt upon, if iurlecd it l.tas l>CL'D uoticcd at all. 

None of the aYailablo ma.terial contain t he questionable mineral, in size 

or pcrfcctimt, suitable fori ola.tion and crystallograpl.lic iU\·estigatiou ; 

hence tho corrcctue s of the view here ad\'auced, that it i · tricliuic, cannot be proven. The ouly other explanation po ' ible is that of an " opt ical anomaly." 

If' this m'ineral be triclinic in crystallization, it is manife tly <lifl'crcut 

from either Dabingtonite or Szab6ite, tbe only known triclinic pyroxcne8, 

am\ form s a new species, whose chemical composition does uot, in all 

probabilit,v, vary greatly from t hat of common ang-ite. Tlte variaU011s 

in optical beha,·ior g~est an lbnalogy with the t1·iclioic feldspars. 

Whetbet· the observed behavior be fi nally explained in acconla.oce 

with th e hypothesis l.tere ad,·oc:atcd Ol' not, an interesting aml important subj ect for furth er in,•cstigation is certainly indicated. 

~di AL CuMPO ITIO~ OF TllE ROCK. 

The rock selected for chemical analysis is that occun-ing in plnC<' on 

the rth ca~t boulder of the main Buffalo Peak. (Coli. No. 144.) For 

a do ·cription of its tructnre and constituents see page 1!). The rock 

was Yery fresh, anti the millerals recognized in it are plagioclase, t wo 

pyroxenes, magn ~ite, and a lit-tle apatite. Between these is a brown· 

ish glassy base. 

Tlte spociftc gravity was taken at a temperature of lGO 0. The analy· 

(25) 
26 HYPERSTHENE-ANDESITE. [Bull.l. 

sis was made by 1\ir. "'.,.·F. Hillebrand, chemist to the Rocky ]\fountain 

Division of the Survey. 

Specific gravity ........•.....•••••••••••••..••. 2. 742 

Si02 ...............•.........••••••.•....................• 56.190 

AlzOa .......... : . ... · .. ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16. 117 

:E'e20a. . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . • . . . • • • . . . . • . . . . . . . ... 

:FeO ........•••.. - - --... - - - -. . • ---•. · ---· · - - -· · -· · · - --· -· _. 

Mn,O .•...•••..•••• •...•.•••• -•.• - - -•• --•. -. - -- . -- --- -- --• • 

CaO .....••.••••••...........•.•.•...•.••................ . 

BaO .••••...•••...•.•..••••........•........•• _ •.......... 

SrO ............•• - -• . . • . • . . • • • • . . . . . . . . • . • • . . . .: .......... . 

MgO . ...••.••• -•.•• --. - -. -- - . - - - -• • • --• • - - - -• • • • - - -· • - - -• • 

N a20 ..... ........ - --- - . - - - -· · - - - -- ---· · -- --· -· - -· · · - ---· · 

K 20 .......... ---- . ----• ·-·--· · ·--· · · • · · · • · · ·- · · · · · ·--· ~ · · 

H 20 ....•......... ---- · ·---- -- ·- · · · · · · ·.· · · · · ~ · · -· · • · · · · · · · · 

p 205 . --- • --- --.. -.. - ---- . --. -- - . -- -- .•• -.. -..... - - -.. - -. .. 

Cl .......•...•........••••.•• -•.••••... -••••..•••......••• 

4.919 · 

4.433 

trace 

6.996 

trace 

trace 

4.601 

2.961 

2.368 

1. 028 

0.266 

0.022 

99.901 

There is but little in the analysis which requires special explanation. 

The percentage of K20 is considerably larger than would be expeet~d, 

as none of the larger crystals of feldspar can be considered as sanidine. 

The amount of .P20 5 found, with the 01, indicates that minute needles 

of apatite must be quite abundant ·in the ground mass, though but few 

can be recognized as such. Ba.O and SrO are seldom given in analyses 

of andesites-probably, in many cases, because they were not sought for. 

ISOLATIO~ AND ANALYSIS OF HYPERSTHENE. 

In order to establish the identity of the pyroxene, which ·seemed 

from its optical behavior to be rhombic, an attempt was made to isolate 

the same for analysis. ·It is scarcely necessar,y to mention in this connection that the desire to comp_are the Buffalo Peaks rock with the 

hypersthene-bearing ande:-:ite of the volcano of Santorin in the Grecian 

archipelago led to the chemical investigat,ions which follow; and it may 

be safely assumed that the chief results of the investigations of Fonque 

on the Santorin lavas are known even to those to whom the final volume, 

with its wealth of minute observations and splendid illustrations, is not 

~ccessible.2 

INVESTIGATIONS OF FOUQUE ON THE LAVAS OF S.A.NTORIN.-Fouque 

fonnd that the lava of the eruption of 1SG6, which at first glance seemed~ 

typical augite-andesite, contained in reality two pyroxenes, which he isolated and l1etermined as normal augite aud h~1perstllene. He also found 

hypersthene in ol<ler rocks of this same volcanic group. It is the first 

~F. Fonqne, "Santorin, et ses eruptions", Paris, 1879. 

(26) 
CROSS.] ISOLATION OF HYPERSTHENE. 27 

inRtance where the presence of a rhombic pyroxene in "augite-andesite" 

has been chemically and optically proved beyond dispute. 

As the so-called Thoulet solution of the iodide of mercury in the 

iodide of potassium was not available at the time the investigations 

were in progress, recourse was had to the method employed by Fouque 

(l. c., p. 190) in separating the iron-bearing minerals of the Santorin 

lavas from the other constituents. 

l\fE1'HOD USED IN ISOLATION OF HYPERS1'HENE.-A specimen of the 

rock was crushed until all passed through a sieve contai'ning sixty meshes 

to the inch. Only that portion of the powder was used which was retained by a sieve having eighty meshes to the inch, as uniformity in size 

of the grains acted upon by the acid is desirable, and the finer powder is 

objectionable on several accounts (See Fonque, l. c.). The grains tbns 

obtained were placed in a platin_um dish, and treated with strong fluorhydric acid, which attacks first the feldspars and other substances free 

from or poor in iron. According to Fonque, concentrated acid is best, 

in which case, in pouring the powder, little at a time, into the acid, there 

is a more or less violent ebuliition without the application of external 

heat. On the ceaRing of this ebullition it may be presumed that a large 

part, if not all, of the easily attacked minerals is dissolved. The action 

is stopped by dilution with water. If matter still remains wllich it is 

desir d to remove, the water is poured oft' and the powder treated again 

with acid. In the present case the acid was not conc ntrated, and 

hence considerable beating was necessary. In all cases the p0wder 

should be ra,pidly stirred with a platinum spatule. On discontinuing 

the action of the acid, there is always more or less gelatinouR silica 

deposited. upon the remaining grains. This is removed by repeated. 

washings and rubbing of the powder under water with the finger. The 

magnetite is then separated with a small magnet. 

A ~:?pecimen of the Bufl'C~JLo PeakH rock (Coli. No. 144) of which the 

· complete analysis was made, treated as above at difl'er·ent t,irnes, yielded a 

powder in which there were only a few white grains remaining. The acid 

did not seem to attack them very readily, and before they entirely disappeared a considerable portion of the pyroxene was also dissolved. Tlie 

residue was finally obtained quite pure, and ~Y ielded upon analysis theresults under I and II below. Fouque found ( l. c., p.195) tllat jf the mixture 

of augite and hypersthene derived fl'om the Santorin lava were further 

treated with flnorhydric aeid, the augite was much more easily attacked, 

as it contabed less iron, and that he could in this w~y finally obtain hypersthene with but little admixture of augite. In the present cnse the 

microscope sllowed a large amount of augite with the rlwm bic mineral, in 

the rock section, but the analysis shows the substance analyzed to have 

been nearly pnre hypersthene; henc.e, it is presumable that the quantit,y 

of pyroxene which was dissolved in removing the white grains above referred to must have been chiefly augite. Microscopic examination of 

(27) 
28 . HYPERSTHENE-ANDESITE • [Bull.!. 

. material left, in Analysis I (which has been made since this was written), 

after the feldspar had disappeared, showed a · decided admixture of 

augite with llypersthene; the augite was, however, remov·ed by further 

treatment ·with acid. 

Another specimen from the Buffalo Peaks, from a boulder in the tufa 

beds (Coli. No. 150), was treated in the same manner. This rock was 

chosen because the microscope showed a large amount of very pure 

rhombic pyroxene and but little augite. The powder obtained was 

examined with the microscope and fou.nd to be almost absolufely free 

from impurities. Its analysis is given under III. 

MICROSCOPIC INVES'l'IGATION OF ISOLATED MATERIAL-The microscopic study. of the isolated cr,ystals and fragments sbO\YS clearly the 

rhorn hie nature of the mineral in question .. The crystals obtained are 

often 0.3mm in length, and 0.15mm in thickness. In all those suspected of 

being rhombic, the pleochroism is much stronger th:--1n has been de: 

scribed for the sections observed in the slide. (See p . 21.) The changes 

in color are from a dark reddish-brown to a very dh;tinct green, instead of 

from greenish-yellow to pale green. Every such prism extinguishes light, 

parallel to the Yertical axis. The grains of augite are more of a bottlegreen color, and only very fair1tly pleochroic. In the p1aterial obtained 

from specimen (Coli. No. 150) affording III, probably not more than 

one per cent. of the grains arc augite. J\fany prisms are quite perfect, 

and it would not be at all difficult to hwlate a large number of little 

crystals of almost the exact appearance of those reproduced by Fouqn~ 

in Plate LX, Fig. 2, of his previously cited work. The crystals in the 

Buffalo Peaks rock are usually stouter than most of those pictnr~d by 

Fouqne, but are quite as regular in form. Fig. 9 of Plate II shows a 

crystal from .the thin section of the rock which furnished the material 

for Analysis Ilf. 

ANALYTICAL TABLE.-For comparison, the coiuposition obtained by 

Fouque for the hypersthene of the Santorin lava of 1866 is given under 

IV; under V the analysis of the "augite" from the "augit-andesit" of 

the highest peak of the "Sierra de Mariveles" in the island of Luzon, 

g-iven by Oebbeke; a and under VI, the analysis by Damour of t!w wellknown hypersthene from St. Paul's Island, on the coast of Labrador, 

as given by Dana. 4 

The isolation of·the hypersthene, and Analyses III and III, were carried out by Mr Hillebrand. 

3 K. Oebbeke, Nencs .Jahrbuch, etc., I Beilage Band., p. 451 (18!:!1). 4 J. D. Dana. A System of Mineralogy, fifth edition, p. ~10. 

(28) 
cnoss.] CO~iPARJS~N OF HYPERSTTIENE. 

ANALYSES. 

I 1.-Butf.olo 1

n .-nuff••lo Uf.-Buffalo , IV.-S.1n· 

I l'cnks. Peaks. I .Penks. t.orio. 

--------j- --- -- --, -- Sp. Gr. 3.307 

SIO• ············ ··-· ······ AJ.o •.••••••.•...•••.•... . 

Fl't0J ..•.....•.....•..•.•. 

51.703 

I. 720 

Q. 30t 

51.157 50. 0~3 

2.1;;.& 2. DOO 

FrO......... .............. 11. oo;; 18. 3<:0 

:UnO...... ...... .......... 0. 303 0. 303 

CnO. . . • . . . . . . . . . . . . . . . . • . . ~- 873 0. 812 

ll ~O. . . . • • . . . . . . . . . . . • • • . 2;;. 001 24. 251 

xa.o . ···················· .... ... .... ........... . 

17.812 

0. 120 

6.600 

21.744 

0. 274 

60. 12 

2. 12 

l .CO 

23.59 

·· ·········· 

10.49 

11.05 

o. 6i 

V .-T.u· zoo. 

M . • iO 

a. so 

2.80 

10.00 

0. 75 

10. 4G 

lO.CU 

............. 

29 

VI.- Snlnt Pnu ~. 

51. 0 

0.37 

............... 

21.27 

1. 32 

s. 00 

21. 3l 

...... ...... 

100. ~u I 100. 001 I 99. 5!),1 __ • _ _____ :- ---- .----

99.&t 99. a:; I 911.72 

The specific g-rn,vit.y of III was taken at 230 0 . 

DtsGUSl:>lON ov A..~ALYS .-In I and n tbe alkalies were uot tested 

for, and in II and Ill :til the iron is gi,·en as FeO, becau e tl.le special 

determinat ion of tl.le protoxide wn not uccessful. 1'he amounL of F(•20 3 

pre ·ent, is in all pr·obability about the same as in I. Tho arnonutof iron 

deri,·eu from ~ra in s of magnetite included in the pyrox ues of Il and 

I rr is mall. 1'110 cr,ystit Is a.re uunsually free ft·oru inclusions of a II kiuds. 

The l\10 0 of II is taken from I, aud is undoubtedly vet·y uea l'!y correct. 

the portion analyzed iu~ det·h·ed from the ~";arne rock. In Ill is iucludcd a. small amount of fcld11 pa.r att.-'l<:hed to I.J pcrst lt e ~rain , an<l 

wl.lich could uot be eli olved without losing too much of t.hc lu.tter min· 

era.!. 

On comparing- li aml Tli with t11e other ann lyses of th o tal•lc, it is cleat· 

that they m·e much nearer to typical hyperi'ithenc (VI) iu eompo ition 

than the rhoutbic mincr·al of the Sautorin hl>,·n, who'• identity with 

hypersthene Ita been recently admitted, e,·en by H.ot>enbusch/ who ba< L 

at fil'st cxpres ·cd doubts upon tlle suhject.

6 The Ynr,Ying- quantities of 

CnO in T.li, Ill, and 1 V ma.y indicate tllat the simple silicate, aSi03, enters more largely into tl.te composition of rhombic pyroxent!, as occurring in rock , tllan ba h<.'retofore been suppo cd. 

Thoouly in rnncc siucc the work ofFouque, known to the writer, wllere 

tlto pleocLmic pyroxene of an "augite-andesite" has beeu isolated anu 

examined with l'<.'gard to it · ct·ystal system, il'! in the cMe of tl.le l'Ock 

ft·orn tho Sierra tle )lari,·cles, which wa: ill\·csti~ated by Oebbeke (l. c.), 

and which ga.,-e S<·hwager the composition V of the table. Oebhel' e 

tina.lly prououuces the miucrnl to be augite and not h~ r t heno. lu 

tl.lis case, a.s in those ment~oned ln.tcr (p. 34), tl.lo gt·onnds given for 

the <lctrrminat.ion . are by no mcn.us satisfactory. 'l'be ouly evidence 

ginn by O(>bbcke in fa.Yor of tl.le monoclinic system is the followiug : 

------------------ 6Roview ofFonl)u6's work on Snntorin, in Neucs Jabrbuch, etc., 1880, II, p. :no. o Roseubusch, Mat!Sige Gesteine, p. 41 8. 

(29) 
30 HYPERSTHENE-ANDESITE. [Bull.l. 

He examined a few of the isolated pleochroic prisms by attaching them 

singly to a piece of wax in such a mar~ner that he coul~l test the direetion 

of extinction parallel to each face of the prismatic zone, and· in each crystal examined he found oblique extinction in some position. The writer· 

found, on examining the material which furnished Analysis III, that 

many pleochroic prisms did not give definitely an extinction parallel to 

the vertical axis when lying loosely on an object glass in air; but that 

the same grains mounted in balsam were much more clear and distinct in 

their optical behavior, and always in favor of the rhombic system. In 

the case of such tiny grains, especially when obtained by the crushing 

of ro~k to powder, the examination of optical properties in the air is 

very unsatisfactory. The reflection of light from uneven. surfaces, the 

disturbing influence of fissures, of included substances, &c., all tend to 

make the optical examination of minute particles in air unreliable. If 

mounted in balsam, the liability to error· is much less. 

The substance which yielded the composition V was isolated by means 

of the Thoulet solution, and would represent a mixture of rhombic· and 

uionoclinic pyroxenes, were both present in the rock~ The figures of 

V are certainly abnormal for any augite known to occur as a rock constituent, but are easi~y explained on the supposition of a mixture of 

augite with a 'bronzite or hypersthene. 

(30) 
CHAPTER II. 

RHOMBIC PYROXENE IN OTHER ANDESITES. 

The resemblance of the Buffalo Peaks rock to that vm·iety of augiteandesite which bas alwu.ys been regarded as most typical, naturally 

demanded tlmt all available examples of the latter shouhl uc examined 

in regard to the character of tlw pyroxenic constituent. '£he particular 

val'iety referred to is that characterizt>d by a glassy base, ofteu brownish 

in color, in which lio a multitude of minute microlites of plagioclase 

and pyroxene, with magnetite grain,. The same minerals occur in porpllyriticindi\"iduals, though by no means so prominently as iu other varieties of andesite. llornblende and biotite are often entirely wanting and 

are rarely abundant. Olivine appears occasionally. Tllis variety is 

e pecially abundant in Hungary, Transyl>ania, and Servia. 

As many of tile rocks examined come from well-known European 

loca.lities, the ob ervu.tions in each particular ca e will be concisely 

given. Untortunately, only t.heir sections, witlJout baud pccimens, 

were available. 7 

In each ection the attempt was made to oh erve and record the 

direction of total extinction in every prismatic section of pyroxene of 

sufficient size to allow exact determination. 

'£ADULATED DESUL'l' OF OBSERVATIONS ON AUGITE·ANDESITES.-

Tlle ratio of prismatic sections with rhomb ic, to those witll monoclinic 

optical orieutn.tion, was fomtd to be in the rock from: 

(1) BolJUnitz, near Scllemnitz, in Ilungary ...•. • .. ........•. as 8: 2 

(2) Podluatl, n~ar Schemnitz, in Hungary ...... . ... . . . ... . .. as 15: 5 

(3) Bagonya, near Schemuitz, in Hungary ... .. ....• . . ... .. . as 13: 6 

(-l) '' Gonczer 'Ihal," near Schemnitz, in Hungary .. . . .... .•.. a 21: 1 

(5} Ober Fernt>zely, not•tlteast from Nagy-Banya, Hungary .. .. as 15 : 2 

(6) Ro ·zaj-Iuguie , northeast from Nagy-Banya, llungary .... a 8: 5 

8 (7) Southea t of Rank, Abaujer Coruitat, Hungary .•.... . .. as 47: 11 8 ( ) Magos Ter, Abanjer Comitat, Hungary ..•. ..•••.•..... . as 43 : 17 8 (9) Between Tul.trina antl Czer>cnicza, Saroser Comitat, nungary . . . . ... .. . .. . .. ... . . . . .•.....•. ..... ... . ... . ........ as 24 : 6 

1 For Nos. 1, 2, 3, 4, r,, 6, and 13, the writer is indebted to Prof. F. Zirkel, of Leipzig. 

NoR. 10, ll, and 12 are contained in t ho "Sammlnng No. 6, von typisclwn vulku.nischon Gesteinon nus Ungarn uml Serbien," prepared and sold l)y H. l•'uoRs, in Uerlin. 

Tllo.material ~ saiu to llave beeu selected au<l described by Prof. J. S?.111J6, in Budapest. 

e Nus. 7, 8, n.nd 9 nrc rocks sent by tho "K. K. geologischen snnR~a lt" of Austria to tho United Stntos Geologicnl Survey of the Fortieth Pn.mllel, uud were k indly 

(31) 
32 HYPERSTHENE-ANDESITE. LHull.l. 

(10) Tokajer Berg, Northeastern Hnngary ... .. ..... ~.!None distl.·nr.tly 

(11) Lorinczi, Matra Gebirge, Central Hungary...... monoclinic 

( 12) Borac, Southern Servia ...... -. .. . . . . . . . . . . . . . . could be found. 

(13) l\tfount Cotopaxi, Ecu~dor, S_onth America . . -... . ...... as 10: i) 

DiscussiON OF T.ABLE.-In Nos. 4~ 5, and 6, only the larger sections 

were counted. There are many of about 0.4mm to O.;Jmm in length, all of 

which extinguish light parallel to ·the \ertical axis. 

The few sections in which the optical behavior was not distinct were 

neglected. 

. The microlites of pyroxene, in cases where they could be tested, seemed 

for tlw most part to be monoclinic, but the determination was seldom 

satisfadory. 

It appears, therefore, that in all those cases mentioned above, a rhombic P3Toxene is much more abt.tnda.nt in porphyritic individuals than 

augite. For it cannot be supposed that such constant results could be 

obtained through mere chance. It is true that sections of augite parallel to the orthopinacoid are not to be distingtiished optically from 

rhombic pyroxene, but it is not possible to explain the above figures iri 

ihat way. · 

The same difference in appearance between the two pyroxenes is to 

be noticed in the above rocks which was described in the case of the 

B~1ffalo Peaks andesite. The rhombic mineral is pleochroic in the same 

inanner (p. 21), while the mQnoclinic is not noticeably so. TIH re is also 

a urfferencc in development. The rhombic pyroxene, wLich, through 

analogy with the cases described, will be hereafter designated as hyper~ 

sth0ne, is better developed than the augite. Its crystals show terminations as if from domes quite fretjuently, and its cross s(~ctions are 

sharper, being chiefly bounded by pinacoidal outlines. The augite 

grains are much more irregular as a rule, and contain glass and mag· 

netite {nchisior1s hi · gTeater ·abundance than the h~'persthene crystals. 

An apparent intergro,vtl:i of t,he two was not unfrequently noticed, as 

in the rocks fr;on1· B·oh unitz' and Roszaj-Ingnies. 

AUGITE- A~i>:Esii:Es OF THE 40TH PARALLEL.-Through the courtesy of Mr: Arnold Hague the slides of the andesitic rocks c'onected 

during the- geological exploration of the Fortieth P~trallel, and which. 

ha\Te beeit described by Prof. F. Zirkel, 9 were placed at the disposal 

of t.he writer.' . The results obtained from the examination of these 

slides agree fully with what bas been stated conceruing the European 

roeks. In· ail bi1t. two of those rocks described by Professor Zirkel as 

~' augite-a.ndesi tes" a very large part of the pyroxene seems identical 

loaned to the writer by Mr. Arnold Hague, United States Geologist, the cnstodia,u 

of the collections belonging to the Fortieth Parallel Survey. The rocks bear respectively the numbers 24, 25, and 19 of the Austrian Survey, and are labeled ''Grauer 

Trachyt, Richthof." They are all typical rocks, in fresh condition, of the class under 

discussion. 

9 .E'. Zirkel, Microscopical P etrography. Washington, 1876, p. 221. 

(32) 
1'1101'8.] RJTO)IIJIC PYROXENE IN AUG ITE ANDEF;ITES. 33 

1\·itl! that which i~ rt>ganlcd as prol>able h,\'!lCl'Stbenc ill the :LUO\'C rocks. 

The two exceptions (Mic. Nos. 514 and 515) arc basaltic in habitus and 

carry oliYine. 

PREYI OUS OBSERVA'tiOXS OF RHOMBIC PYROXEN.E IN AUGITEANDESITES. 

JIT ~TOIUOA .-TII c lllllllher of im~tan ces lniO'i\' 1'1 to tho writer wllcre 

t.l!e JH'C8encc of rhombic pyr-oxeuc i11 '· augitc·amlc:sit'es" l1 as beeu at 

all ernpllasized is extremely small; J. Niedzwiedski 10 e~crib d in 1872 

a rock froltl St. Bgidi, in Steiermark, as "Hypersthen-Andesit." In 

1877 this rock is 111 eutione1l by Rosl:'ubnsch 11 as the single rock known 

which can bear that name. In 1880 B. Hus~ak 11 prononuce.d it an ordi· 

nary augite-audesite, and, so fa.r as the writeP.is aware, bis verdict has 

not been questione1l. Reference will again be made to this case lat,er. 

The occmrcncc of rhombic pyroxene even as an aacessory constituent 

of augite-ande ites has been but rarely announced. 

R. von Drasche 13 has mentioned bastite as occurring iu augite-andesite 

from Videna, in Steiermark. 

Rosen busch 1

' at the time of issuing his often cited work (1877), while 

not denying tha,t a rhombic pyroxene may occur in augite-andesites, is 

still inclined to considet· those pleochroic prismatic sections of pyroxene 

in which light is (lxtiuguished parallel to the ' 'ertical axi~1 as chance 

sectio11S of augite parallel to the ortho-pinacoid. It is in great mea.:.;. 

ure owiu g· to this judgment, no doubt, and to the undoubted presence of 

pleochroic augite in recent rocks, that many observers ha ,·e seemed to 

dismiss all thoughts of rhombic pyroxene if in the same slide with pleochroic sections, such as have been described, uOt·mal augite wit h its 

oblique extinction could be found. Thus, E. Russak (1. c.) disposes of the 

bypcrstbene andesite of Niedzwiedski with the simple assertion tl!at tl1e 

pyroxene is monoclinic, because he has found apparent prismatic sec-

' tions in which extinction took place at more than 300 from the \'ertica l 

axis. 'Inasmuch as he bad previously continued the statements of von 

Dr-asche 15

1 it seems highly probable that augite is uot s pecially abundant 

in this andesite. 

1oJ. Niedzwieclski, T11chermak's Min. nnd pet., Mittheilnnglln, JV, 87~, p. 2.')3. 

" H. o~on'lluso h, Mnssige Geateine, p. 480. 1" E. Hussnk, Nones .Jnhr'lluoh fUr Minoralogi e, etc., 1880, I. p. 289. 13R. von Dmsr:be, 1'llchermak's Min. und pet. Mitth. , 187:1, V. p. 1. 

~<H. Rosenuusch, Mttsaigo Ool!teino, p. 411. 

1•E. Hussak, Vorhamll. rl. k. k. Geol., Reiohsanstnlt, Vicmm1, ltl78, p. 338. 

(33) 

Bull.U-3 
34 HYPERSTHENE-ANDESITE. [Bul!.l. 

Russak 16 has also published the results of microscopic investigations 

on the eruptive rocks of the region about Schemnitz, in Hungary. While 

the rocks of this district have been frequently studied by eminent investigators, such as Zirkel, voni Rath, and Doelter, ·the publication of 

Russak is here considered as the most recent lmown to the writer. 

Augite-andesite, of the type especially under consideration, is Yery 

abundant near Schemnitz. Russak mentions a large number of occurrences, among them those of Bohnnitz and Podhrad, and the great similarity of most of them is evident. The pyroxenic constituent is always 

called augite, although some of it extinguishes light parallel to the vertical axis. Decomposition products resembling bastite were also noticed. 

The pleochroism is quite strong and the pinacoids are markedly predominant. The angle of extiuction in two cases is given as 470 and 480. 

The general description given by Russak corresponds closely to that 

required by the two slides in possession of the writer, from Podhrad 

and Bohuu.itz, except that no allowance is made for two species of pyroxene. 

The short description accompanying the slides of the Fness colleet.ion 

(see p. 31) mentions no other pyroxene than augite, even in those 

cases where eYery prismatic section seems to be rhombic. 

The determination of hyperRthene in the lavas of Santorin, and the 

st~~tements of Oebbeke concerning the pyroxene in the "augite-andesites" of the Philippine Islands, have already bet>n cited. (p. 29.) 

In all other descriptions of or references to augite·andesite of the 

chief type which have come nuder the observation of the writer, it is impossible to obtain satisfactory data concerning the pyroxene. In nearly 

all of tbem, Jwwever, the pleochroism and predominance of the pinacoids are dwelt upon, which, in the light of the present investigation, 

justifies the suspicion that rhombic pyroxene is not wanting. Two instances will be given where -the existing descriptions of ~' augite-andesites" suggest the identity of the supposed "augite" with the rhombic 

pyroxene of the rocks here described. 

Rosen busch 17 mentions that the augite of the "augite-andesites" from 

Chimborazo and Tungnragna, in the Andes of South America, is strongly 

pleochroic- Artopc 18 has given analyses of several augite-andesites from: 

the .AndPs, among them being two from Tunguragua. · One of these 

shows nearly G per cent. -:\1g0, while iu two other cases nearly 4·per cent. 

:M:gO is given . The augite-andesite fmm Cotopaxi, examined by the 

writer, showed 10 apparently rhombie pyroxenes to 5 monoclinic . 

.Again, Cohen1

" •lescriues the porph.)Titie augite crystals of two RaWE. J-Iussak, Sitzuugsbcricht <1. k. Akad. d . Wiss., Vienna, July, 1880, p. 164. 

17 Rosenbusch, Massige Gesteine, p. 420. 

1SArtopc, ' ' Ubcr angitl1altige Trachyte der Aud~u," 1872. Gilttiugeu. 

I9E. Cohen, "UberLaven vou Hawaii, " etc., Nenes Ja.hrhuch, etc., 1880, II, pp. 38 

and 5~. 
CR08S. j lU!O~IIHC PYROXENE IX DIABASE. 

waiiau ~ndcsite11 as '' kriijtig pleoclu·oitisclt iu the ~;amc mantwr shown 

in tho Bufl:tlo Peaks ltypet· thcne: while the microlitt•s in the g round· 

mass do uot Cl'lll t.o l>o ISO. Also, tl!c augite of an ·' .·l ttgitallcieiJitbimlltein' 

found between Xcw Britain and w Irelaml, in the SoutiJ Pacific Ocea n, 

is strongly pleochroic in the sante manner. 

UJIOMRIO P\'ROlRSE I~ JJlAIBSIC JtOCKS. 

'l'l.lo possiuility tJ.w.t a 1'110ml>ic pyroxene may occur iu some augite· 

andesites has been ndmitte>d by Rosenbnsch ,

20 who, whilo !lenying- that 

tho Illcocltroic pyroxc11e, so common in augite.andesites, h; rlJOmbic, ex· 

preSISCS a belief that t he final diseo\·ery of a rhombic pyroxene in a sub· 

group of the augite-andesites is eYen J:!.ighly probnble. 'l'hi probabil· 

it~· ariS{'S out of analogy with the diabase-porphyrite>s of the left bank 

of the J.~ower Uhinc, which coutain enstatite. It is interesting and significant lltat tlti::~ analogy i · borne out in Colorado. 

ENSTA'l'J'J'E·BEARING- DIABASE FROM COLORADO.__:At .Morri ·on, near 

Den>cr tht·re is in the Archreau gnei s a narrow dil;e of a <lnrk aphan -

itic rock. Under the micro cope this rock is seen to ~o i t chiefly of 

narrow pri rus of plagiocla. e aud a colorless pyroxene. The an ..,.ular 

space betwt:en the c arc filled in part with a colorlc ani otropic 

mineral, which mny be ortbocla e, and with a <lark groundma The 

ore is apparent)~ magnetite, and is almost cxclusi,·ely confined to the 

g-round mas ·, where it occurs in regular aggregations, and seldom in 

single grai ns. Tltese- aggregations seem often like dcvitriflcntion products, ancl a glass base is in places to be identified. The pyroxene 

occurs chictly in prisms of about 1mw in length by 0.2'" 01 i u thickness. 

All such indi\'icluals arc co!orless, have nurucrou!S eross.fissut·cs, and 

extingnisll light when the Yerti<ml axis is parallel to t he principa l section of one of tho cro eel nicols. The cross-sections sltow a dominant 

deYeloprnent of the piuacoids. The cleavage is mo t pronounced parallel to the pri ·m, bnt there nrc many irregular fi ' ·nrc , aud omc parallel 

to the pinncoiu . 

The absolnto identit.y of this mineral with en tatito has not been 

prO\'eu, but. there e<1ms to be no goo<l reason for doubting it. The 

remaining ))yroxene is in maller prisms and has a Yet·y light pinkish 

color. .J: cal'ly all of the e pri m · ha\e an angle of extinction exceeding 

300, and they beloug nudoubtedly to augite. 

Tbc age of thi · rock canuot be determjned, but it has throughont the 

habitus of a Pre.Tortiary ernpth·e. 

RUOAIBIC PVROlF.SE IN IIOilSBLI:(NDE·A NDt:Stn:. 

Tlle prcsouco of a. rhombic pyroxene in th e ltot·nblcu<l<•-biotito-andesites ltns been seldolll auuouuced. 

Rosc ulltl sc , ~lus~igc Gesteine, p. 411. 

(35) 
B6 HYPERS'l'HENE-ANDESl'l'E. [Bull.1. 

. Hosenbusch 20 found it in one dacit-e ; Lagorio 21 fouutl pyroxene in certain andesites of the Caucasus which acted optically like a rlwmbic 

mineral, yet he does not Jlronounce it such. 

In the hornblende-andesite from Buffalo P eaks, pyroxene, wholly 

.analogous to that of the hypersthene-andesite, is quite abundant. In 

the tnfas of the ·same locality hypersthene is often associated witll lwrnblende and uiotite . 

.A slide in the possession of the writer, from Moisar (Mocsar ), · iu 

Hungary, shows hornblende, biotite, and appal'ent hypersthene. The 

groundmass of this rock is much less prominent than in the typical 

., augite-audesites," yet seems to be essentially of the same character, 

and the occurrence may represent a tran~ition form. 

The Fuess collection (see note, p. 29) .contains two beautiful llyaliue 

andesites from Gorni Milano-vatz, and Slatni, in Central Servia, in which 

the pyroxene seems to be rhombic, with scarcely an exception. Horn 

blende and biotite are abundant in the same. On the other hand, the 

pyroxene in the andesite from Jakuben, near Tetschen, in northern 

Bohemia, though strongly pleochroic, is still nnmistakeabl,y augite. 

The pleochroism of this augite iR, however, very different from that 

which is characteristic of andesitic hypersthene. .Augite, sometimes 

faintly pleochroic, can often he found in andesites and trachytes of the 

Siebeng birge~ the .Auvergne, and other districts, but in these cases · 

sections with rhombic optical action are very rare and cannot be considered as indicating a rhombic minera1. 

CLASSIFICATION OP ANDESITIC ROCKS. 

NEED OF .A. RECL.A.SSIFICATION.-The group of the andesites, including all Tertiary eruptive rocks with plagioclase and. one or more of the 

minerals hornblende, biotite, or pyroxene as essential constituents, is 

more in need of a natural subdivision than any other in the category of 

modern petrography. This statement will hardly be disputed. 

The division into hornblende and augite-andesites has often been assailed, with justice, on the ground that very many rocks contain hornblende and augite in about equal quantity, making the transition stage 

of as fl'e·quent. occurrence as either of the extremes. On the other hand~ 

the division of the augite-andesites has been justly defended, by pointing to the ''original," or the typica.I rock, in which hornblende and biotite 

seldom play any other than a Yery subordinate part, and which has been 

20Rosenbuscb, Massige Gestt- ine, p. :300. 

~A. La.gorio, "Die Aml e,.ite fl es Ka.nkasns," Dorpat, 1878, p. 18. 

(36) 
CROI!tl.) ;RECLA::!SlFI<.;ATIOX OF ANDESITE .. 37 

found in willtlly separated patts of the world, with a truly reUtarl;aulc 

per~i~teuce of charactel'istic . 

A glanco at the rocks which, according to the prevaili11g principles of 

dassiflcation, must ue called a ngite·andesites, shows three subdivisions. 

At oue extreme arc those rocks upon whose characteristics the objections 

to the prevalent ch1s ification are grounded. 'fbeso occurrences, united 

with thegrea.t uutjorit,y of omb nde biotite ande~S ite · nre usually charactcl'izetl by\\ trachytic habitus. In these, feldspar is by far tl.tc dominant 

element.,andofteu sauidin forms a.nimportaut partof it. The structure 

-of the gwundmnss is pn vailiugly much more crystalline thau iu the 

so-called augite-andesites proper, and plagioclase is especially abundant 

in it. Qtutrtz or tridymito is often present. 

At th.- other extreml\ are t.l.1o rocks, COIIIJHU'at.h·ely few in numbe1·, 

wl.ticu, thougll posse.ssiug tho basaltic habitus, are ~r.i ll stt·ictly aude-

.sites tlu·ongh the abseuce or rarity of oli\'inc. A:~ examples of this 

.class may be cited numerous rocks of t lle A nvergne described by von 

Las~~ulx,12 a nd tlle rock f•·om the Lowenlmrg in the Siebengebirge, commonly called " tlolerite," hut clas, ified by Ros{'nbusch23 with the a ugite-

.andesite::;. Between th es~ a.re tlte normal "augite-andesites." 

micall y considered, the andesites with tracl.lytic habitus are somewhat clitlerent from tile normal a.ugite-amlesit~. 'l'lle percentage of 

silicn is uoticeably higller. Thns Lagoriou states concerning the anu esites of tile Caucasus that they vary iu amount of silica from Gl.33 

to 77.40 per cent. Do ltcr ~ gives the varintiou in qmu·tz-beariug audcsitl'S of Transyh·auia and Huugary as from 57 to G9 per cent. The 

typical augite-andesites seldom contain more th an 60 per cent. silica, 

Jt·rHl tho average runs quito constantly between M and 58 per eent.26

• 

'fho s •para.tion of the uormal augite-andesites from tllose with tracbytic 

l1abitns llas often been justified by their geognostic relations. Near 

S<·l• muit~, in Hungary, where both types are abunuantly represented, 

the augite-anuesites prope r wer e long ago eli tingnished as "imcllytes 

3trmit:itreu.c" by Bendant. Von Andrian states as a result of the geolog-

:ica l survey of the region inl8G5, speaking of the "jiingere andesite," tuat 

"Ubergiinge in den (amiJlhibol-) andesit lassen sich attch da, too beide neben 

einanrlc1' rurlwmmen, nicht1uwkweisen." (Cited as above by Hnssak (1. c.).) 

lu uwny othe1· places tho uormal augite-audesi te bas beeu diRting11islled 

fi'Om the'' trachytic'' \'al'iety, a · younger. 

' 2 A. v. L:umulx, Neucs J nhrhock fUr ~lio ., etc., 18i0, p. 69:J, nocl1871, p. 673. 

"" Ro:!cnbusch, Uassigo Gesteine, p. 416. 

'' A. Lngorio, " Die Aodosito llos Kaukmms," Dorpat, 1878, p. 13. 

''6 C. Doolter, Tschernutk's Min. uuu pet. Mitth, V. 1873, p. 51. 26 F. Zirkel, Mi c. Pet .. of 40th Pnr., p. 22'~; also the well-lmowo tables compiled 

b y J. Roth. 

(37) 
38 HYPERSTHENE-ANDESITE. [Bull. I. 

RESULTS. 

1. An apparently typical augite-andesite from the Buffalo Peaks is 

found to contain hypersthene as its chief pyroxenic constituent. 

2. The remaining pyroxene of this rock must, from its optical behavior, 

be considered either as· triclin'ic in cr,ystallization, or as augite with 

anomalous action through some unexplained cause. The occurrence of 

apparent twins and of intergrowth with hypersthene render t'b.ejormer • 

explanation most plausible. PyroX!ene with similar behavior wasfound 

in many well-·known augitic rocks. 

3. In all so-called "augite-andesites" 'of the t-ruly typical character 

which are accessible to the writer, twenty-eight in nqmber, the greater 

part of the pyroxene corresponds optically and structurally to the 

hypersthene of the Buffalo Peaks rock. 

4. There is nothing in the current description of the" augite-andesites'~ 

referred to, which can be regarded as positi'oe evidence that hypersthene 

is not abundant'in them. 

5. In all so-called "hornblende-andesites" with a structure similar to 

that of the typical" augite-andesites" which w~re examined, some iirteeu 

in number, the same apparent hypersthene is more or less almndaut. 

6. Tbe pyroxene of those andesites with -" trachytic habitus~' Rcems 

to he normal augite. 

7. The conclusion is that the chief subdivision of the augite-an<lrsites 

may much nwre properly be called hypersthene-andesite.. To this latter 

group are to he added certain rocks containing hypersthene, which have 

been classed with the hornblende-andesites. A separation of the remaining andesites into augite and horn blencle-biotite hearing groups 

does not appear justifiable. 

It doe~ not seem probable that future investigationR will show the oecurrence of hypersthene to be SO closely flOnnected with a certain structural form as is indicated by the preceding observations. If, however, 

it should prove to he the case, the group of the hypersthene-andesites 

will be one of the best defined in petrography. 

It is hoped. that tile correctness or falsity of the ahoYe conclusion will 

be speedily settled by other determinations of the nature of the pyroxene in the so-called augite-andesites. 

(38) 
il S f~~:OLC<;ICAL SlJRVI::Y 

·~ 

....) 2.1 .. 

I. 

' ' ' 

\ 

\ 

I 

I 

' I 

I 

I 

I 

BULLETIN N0. 1 PL ll 

Ftg. ti.ljl 

5. ~(J 

1 

INDEX. 

Page.. 

Autei, LtmchH co, Germany, Ltm ite-bas.:~Jt from..... ................. . . .. 25 

JEt ~ cruptiou of 1537, Basalt from . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2~ 

Analy&is of hypcJ"I!thcuo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

Anal~•s s of bypcrsthouc-nndeRito. ..................... .• . . . .. . . . . .. . . .. . . . . 26 

Amlesitic rocl<ij, Ch st~ificntio n of ...... . . . . . . ....... ......... . .............. 36 

Anclesitcs, Rclntivo ago of............ ............ ........ .. ..... . . . . . ..... 16 

Arcbtearr grnnito...... ............ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1::1 

island ...... ....... . ........................ . ... . . . . .......... ... lt 

Augite-nndeRito <lcfi necl............. ..... ... . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . 37 

, Triclinic pyroxene iu .... ...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Authors : Andrian, vou; geological survey of Schemuitz........ .. .. . . . . . . . . 37 

ArtotJ6; anal.v!li!l of augite-andesites from t he Anlles...... . . . . . . . . 34 

Bond ant; trachyleB u millilrrux of Scbcmnitz....................... 37 

Coht>n. E.; Hawaiian andesites.. .......... .. . .•. .. . ... . . . . .. • .. . :15 

Dmw, J . D.; analysis of hypersthene................ .. . ... . . . . . . :.!8 

: Dooltc>r, C., 011 rhombic pyroxene in augite-andesite.............. 34,37 

: Drat!CbP, R. von, on rhombic pyroxeno in augite-andesite . . . . . . . . . 3:3,3-1 

: }' ouqu6, !!'., on thela.vas of Santorin .. . . .. . . . . . . . . . . . . . . . . . . . . . . . 2R, 28 

Fuesa, R.; hyaline andesite slitles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1, :Vi 

Hague, Arnold. ou gite- ~ndes tes of 4oth para llel . . . . . . . . . . . . . . 3'2 

Hillebrand, W. F.; nnalysis of hypersthene . .. ... .. . . . . . . . . . . . . . . 'l8 

Hnssnk, E., on hypersthene-andesite .... : .... . ............... . .. . :la, :14,37 

: LtLgorio, A., on pyroxene in nndesito from t.ho CnucusnR....... . . . :!6, 37 

: Ln an x, A. von, on rocks of the Auvergne. .... .. .... ... ... .. . .. . :17 

: dzwi ll ki , .T.; hyprrsthcne-nnclesite . .. . . . .. . . . . . . . . . . . . .. . . . . :33 

: Ooi.IIJcko ............. .... . . ........... ... . .. ... ...... ........ .. . 28, 29,:14 

: Ratb, Von, on rhombic pyroxene in uugitc-ouclesito.............. 34 

: .Rickthofon ; claseiflca.tiou of volcanic rocks .... . ...... . ......... .. 17 

Rosl\nbuscb, H., on hyp<'rstbeue-nndesite ......... .... .. 29, :3:3,34, 35, 3(}, :l7 

Roth, J. Table!l compiled l.ly . ...... .. .... .. .. .. .. .. ...... .. . .. . :J7 

Schwager, Taules compiled by. ..................... ....... .. .... 29 

znl.lo, J ., gelcctccl nntl clt>scribed augite-andesite................. 31 

Zirkel, 1-'., ou ungitc-andesite . ......... .. .... .. .. . . ... .. .... .. :H, 3:1,34,37 

Auvcrgue, Rhomhir-pyroxcnu iu andesite and trachyte from the . . . . . . . . . . . . 36 

Ba.biogtorlite.... ..... ....... ........ ....... .... ... . .... ...... .... . . ...... .. . . .. ..... 2:> 

Ba~onyo. near <'homnitz, Hungttry, Angite-unclcsitc from .................. :n 

Baryta. in nnclesito .... ... . .... . ... ...... . ... .. .... ...... .... ...... .. . ... .. ~I) 

Ua ~:~alt, Tricliuic p,v rox'cno in..... .......... . ..... . ... ............ . . . .. . . . . :t3, 25 

nastito in nugitc-audesito .. . ... ··--·· .... .. . ... .. .... ... ... .. . .... ...... .. . 3:3 

Beodant; trachytes somit·itrcux of Scbemnitz .. . . .. . . . . . . . . . . . . ..... .. . ... . .. :i7 

Bildsteiu, Vogelsberg, Germany, Basalt from .... .. . ......... .... .......... . 25 

Bjorfvas, Dol arne, Swollen, Di ~bnso from . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Hinck llill, Gl'ologio stl·ucturo of.. .... . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . .. . . 12 

Bolwuitz near Schemuitz, ITuugary, An~ite-nndc itc from .. .... ............. 31 

Bolvershnhn, Sioucngcl.lirge, Germany, Andesite from . . . . . . . . . . . . . . . . . . . . . . 24 

Borne, outht>rn ervin, Augite-andesite from. ..... ....... ....... ......... . 3:~ 

39 
40 INDEX. 

Bnfl':\lo Peak11, Ele,·ation nf. ..... __ .............. .......... ...... ......... . 

, Oenernl strnctnro of. ..... . ... .... ---- .. ____ ............ ... . 

, Relics of :1. crater on ______ . __ . ________ ........ __ __ ..... __ . __ 

, oot ion of __ .. __ ... __ . . __ . __ __ . _______ .... __ •• __ . __ ___ .... __ 

, Virw of .......... __ . ____ . .. . .. .. __ .. __ ....... __ ..... __ __ __ 

Burg iu Na..s.mn, Go•rmany, Diubi\Se from .. ---- . __ . __ . ...... .... -- __ __ .... __ 

Cambrian •ttlltrt:dtc, Thickness of. ......... ...... ------ __ __ ---- -- ..... __ __ 

Ca rhon i ferou" or B lou· L i mostone, Tb ic),;ne.<JS of .. ____ .. __ • ____ .. . __ ....... . 

Cttncnsns, ndesite~ frnm ......... ......... . ..... __ .... ... . ............ .. . . 

Chimbornzo, Rhombic pyroxcnP in angite-auclosite fr·ou1 .. .. . ..... . ........ . 

Clnssiftc:<tion of 1\uclcRitic rockR __ . . __ ... __ . . . .. . __ . . __ .. ________________ __ 

Page.. 

:~ 

:~ 

16 

14 

24 

l :J 

:~ 

:16,3i 

34 

:lG 

Coal measures, Upper____ .. __ . ____ __ .. __ ... .. . . ____ .. . __ . ____ .. ---- .. __ .. . 13 

Collen, E.; Hawaiian nn<1esite11 . __ . __ ...... __ .... __ .... .. __ .... .... __ .. .. .. ;j;', 

Cotopaxi, Ecunclor, Sonth Amcl'ica, Angite-aude tt•s from . .. ... .... ...... . . :!4, =~~. ;{;') 

Crnnznbl, Snxony, .H11sa lt from __ .. -- . __ ....... .. -- . . ... ... .. . . .. .. __ .. .. .. ·. 25 

Dacite (rhyolite f) __ . .. __ -- ....... __ -- ____ ....................... __ .... --.. li 

Daun, J. D.; n ualyscs of hypersthene ___ ......... . -- . . . --. .. .. .. . .. . .. . .. . :a! 

Dinbnse, Tricliuic pyroxene in .......... ...... __ ...................... __ . . . ~4 

Doclr~r, C .. on rhomhic pyroxene in a.ugite-unclesito .... __ .. .... -- .. __ .. __ .: :14, :~7 

Dolerite, Tricliuir pyroxene in .~ ........ ____ ........ ____ ........ .... ------ l.!!'> 

Drnsche, R. \'Oll, on rhombic pyroxene iD augite-nndet~ ito .. .. . .. . . . . . . .. .. .. :1;,1, 34 

Elbingcrodc, Hartz, G~rmany, Diabase from .. ... . __ .. __ .... __ __ __ . .. .. .. .. :.!4 

Eustatito in tlhtbnso from Colorado-- ...... -- .... ----•.. -- ... ...... -- .. ---- J5 

Erosion, GlaciaL .. .. __ . ............ __ .... __ ...... -- ... -- ..... ----. . . . . . . . . 16 

1-'lnorbydric ncid, Separation by __ -- .............. ...... .. .. -- ---- ---- .• --. 'rt 

Fortieth para111'1, Augite-andesite of. __ . __ .. ...... __ ........ __ .. . . .. . . . .. . . 3-l 

Fonqu6 1-'., on tho ltwns of Sl\ntorin .. __ .... ____ .... ____ .. . . . . . • .. .. .. .. .. .. 26, 2tf 

F ness, R. ; hyaline nndisitoslides ......... . ____ .... ...... ... ... .... .... .... 31,:«> 

Fnlgnrito ofBuffl\loPenks.... .. ...... .. . ... ...... .. .. .... .... .. . . .... .... 14 

Glncinl erosion ...... .......... ------ ...... --·--·...... ............. . ...... W 

"Ouncr.or 'l'hnl " Hl'nr Schemuitz, Hungary, Augitc-nudcl!it,es fr11m ......... .. :31 

Gorni, Milanovntz, and Sla.tni, Servia, Hyaline t\ ct~it.u fl·om. . . ..... ... . ... 3& 

Omnit<', Arch ronu . .. . .. .... ...... . .. ... ...... ...... .. ... .. .... ...... .... . 1:l. 

Hngne, Aruolol, Assistance rendered b y... ... . . ..... .. .... .. . .. . .. . .. .. . .. . 3-l. 

Hur h~nbcrg, Lnncher Soo, Germany, Nepheline basalt from.. . . ............ ~'> 

Hillt.> rbmucl, W. 1•'.; annlyst.>s of h yperstlteue ......... -- . ........... . •. . . . . . :S 

Holmestrnml, Swl'dcu, Basalt fron1. .. --.................... . ......... -- . .. . 2.S. 

llorubl ntlc-n ncll'~itl', Peculiarities of pyroxene in .......... .. .. -- .... -- . .. ~ 

. T ril'li uic pyroxene in................ .... ...... ...... 24 

llnl!l<al;, E .. on hytl<'rSiheue-audeMite ........... .......... ............. ...... :l:J, ::.t, 37 

llyalite of llnll'nlo Peaks .......... __ .... ........................ --... . .. • . . 14 

llypersthcne, IR<llation of ........................ . .......... .. .. .. .... __ .. ~7 

B ypcl'lltheuc-nudOtlite, Ch t•mical composition of............ ....... .......... :!5 

, Dcacription of. ....... -- .. ....... . ....... --.. • . .. .. .. 19 

, Geological occurrences of.-- .. . .. • . . . .. .. .. .. . . .. . . .. lf> 

llkcrulorf near Notl.'ltln, Saxony, Diabase from ...... . ..... .... .'. ........ ..... ~ 

lslan1l, ArchuJII n ..... .... ... . .. . . .. . ... ... .. .. .. .... ... . .. ... . .... .... .. .. U 

Ju.knlmu, Bohemia, Andesite ft·ont ...... ...... ...... ...... .. ........... ... .. . :!4, :.!6 

Lngnrlo, A., nn pyroxene in nmlesite from the Cancnsns................... :lli, :11 

Lnsnnlx , A. von, con rockM of t bo AnYergne ....... . . . . . . . . . . . . . . . . . • . . . . . . . . :rr 

Leu cit e luva, 'l'riclinic p yr oxene in ...... . .................................. ~;, 

Lim~ tou e altered by solfa.t.nric action ...... .................... --.. ...... . 16· 

Little P la tte Ri"er ..••. .. __ ....... .......... .................... --- ... ... . 12 

Lol'iuczi, Mtl:tra. Gebirge, Hungary, Augite-andesite from ............ ... --. . :12 

Lowen burg, Siebengeuirge, Germany, roterite from .. __ ...... .. .... . .. . .. .. 25, :n 
lNDEX. 41 

Page. 

Lower quartzite................... ......... . ........... . .................. ~ 

Luzon, Augite-an dcsi.t e from.... .. .. . ........ . ...... ....................... :!~ 

Magos 'I'cr, Abanj er Comitat, l:Luugary, Augite-andesites from . . . . . . . . . . . . . . :n 

Meiches, Vogelsberg, Germany, Nepheliuitc from..... ......... .... ........ . :!5 

Meissner, Hesson, Germany, Dolerite from.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Melaphyre, Triclinic pyroxene in .... .... ..... . .. ........... . ........... -. 24 

Moisar (Moscarf), Hunga.ry, Andesite from............. . . . . . . . . . . . . . . . . . . . . 36 

Morrison, Colorado, Enstatite-bearing diabase from . . . . . . . . . . . . . . . . . . . . . . . . 35 

Mosquito Range, Elevation of.. . ........ ...................... . ..... . . ... . . 11 

Nephelinite, Tricliuic pyroxene iu ...... .. . ... .... .. .. . . . . .. .. .... ...... .. . 25 

New Britain, PleoclJroic augite in andesite of. . .... . . . . . . . . . . . . . . . . . . . . . . . . . 35 

New Ireland, Pleochroic augite in andesite of.................. . ..... . . . . . . :1r. 

Niederrncndig, Laacher See, Cormany, Leueite basalt from.. .. . . . . . . . . . . . . . . l!r. 

Nieclzwiedskie, J.; hypersthene-andesite.. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 

Oebbeke ................................ .. ...... . . ........ .. ............. . 28, 20,34 

Obcr Fcrnczely, Iluugary, Augite-andesites from . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 

Olivim•, Rurity of, iu audesite . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . 37 

Opal a. I tera.tion ; product of chalcedony . ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

Pala;ozoic, In l.Jed<l d porphyry in .... , . • . . • • . .. . . . . .. .. . . . • • • . . . . • • • . .. . l Z 

Palreozoic, Tbiclmcsf! of . . ........ ............ .... ... : ........... . .. .... .. i 11 

Plate I describr<L . ................ .......... ... .. : . . . ... . . . . .. .. . . .. .... .. :~ 

Plate II ~scri bed ....... . ............. .......... ............ ......... .... . 

Podhrau uear Schemnitz, Hungary, An~;itc andesites from ... . ........... . . . 

P orphyry in Paheozoic .... .......... .. .. .. ... ... . ............ .. . ......... . 

Rank, Abanjer Cornitat., Hungary, Augite-andesite from ........... ..... . .. . 

Rath, Von ..... . . ................... . ....... . ..... ...... ................. . 

Reclassification of andesites, Need of ........ ... ............. . ....... .... .. 

Reichsanstalt of Austria .... . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .. .. .. .. . 

21,20 

31 

12 

31 

34 

3G 

31 

Rhombic pyroxene in Buffalo Peak andesites ... ........ ........... ... 1...... 2(; 

Rlwml.Ji cpyroxeno in d iahasic rocks......... . . ... .... .. ...... .. .... . ....... ill 

otl1er nndesite ..•.... ..... ... . .. . •.. . . . . . . . . . . . . . . . . 3i> 

, P roportion of, to monoclinic pyroxene in augite-andesites . :n 

Rhyolite, Cry81alline.... . ...... . ....... . .. . ... . . . . . . . . .. . . . .. .. . .. . . .. . . . . 12 

, (Dacite f)... ... .. . . ............ .. ... ....... .... ...... . . . . .. ...... 1~ , 17 

Ricbtloofen; classification of volcanic rocks . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . 17 

Robschitz near Biliu, Bohemia., Nepheline-basalt from ................ ...... -.!5· 

Rosen busch, II., on llypersthcno-a.udesite ..... ........ . ............ 29, 33, 34, :i5, :i(i, :r. 

Roszaj-lugnies, Hunga ry, An ite-andesitet~ from .......... .... ..........•... 

Roth, J., Tables compiled by .. . . ........ ......... ................. ... ..... . 

Rough-and-Tumbling Creek . . ....... ........................... .... ...... . 

St. Egiili in Steiermark, Hy persthene-an<lesito from . . .. .. . ... .. . .......... . 

St. Pmll's Islaml, Hypersthene from . . . . ............ . ..... ....... ...... . .. . 

St. 'Vendel on the Nahe, Ge1·many, .Melaphyre from . ... ... . ....... ... .... . . 

Santorin, Analysis of hypersthene from . ............. ..................... . 

, Hypersthene-andesite on .......... .... . .. . ........ ... .. . . ...... . 

Schwnger, Tables con1pilcd by ...... . .......... ...................... .. . . . . 

Sbeep Hi<lgc ..... ................. ...... ....... .......................... . 

Siebengebirge, Germany, Dolorite from ..... . .... . . ........ ...... . . . .. . ... . 

Sierra de Mari voles, "Augit-ande&i t" from ............................. .... . 

Silica, Percentage of, in nudesites .•.. . ... .. : . . ..... .. . ............. .. .. . . . 

Silurian lime:;~to , Thickness of .. . . . . .. ... . . . .... ......... ........... .... . 

Slatui, Servia, Hyaline-andesite from ............ ............... ........ .. . 

Strontia in andesite .... . . .. . ... ... . . ....... .. .. . ... .... .. . . . ......... ... . . 

Szabo, J., selected and des<:ribed augite-andesites ... ..... ..... . .... . . .... . . 

ab6ito ........ ······ .... .. . ... ..... ....... .... . . ...... ... ........... ... . 

:II 

:li 

· 

33. 

28 

24 

zg. 

26,:34 

2!) 

12 

23, 36 

2tl 

37 

}:{ 

36 

2G 

:n 

25. 
42 INDEX. 

Tertiary eruptive rocks in Colorado ...... ................................. . 

Thoulet solution ....................................... _ ............... . . . 

TokaJer Berg, Hungary, Augite-andesite from ..... . ....... . ...... . ...... .. . 

Topography, Relation of, to geologic structure .. •......... _ ...... . .... . .. . . 

Trias in South Park .................. ... _ ......... _ . . __ . __ .. . _ . . __ .. . .... . 

Triclinic pyroxene in andesite ....... . ... . ............. . ....... . . ... . . ... . 

other rocks ................. .... __ . .. . . -. .. .. . . . .. -.. 

Tridymite present in andesite . ... _ ..... _ .. _ .... . ...................... . ... -. 

Tufa-beds, Composition of. .. ... .. ___ . . ............................ __ .. _. __ 

, Section of ..... . _ . _ ........................... _ .............. _· .. 

Tuhril1a and Czervenicza, Saroser Comitat, Hungary, Augite-andesites from 

Tunguragua, Rhombic pyroxene in augite-andesite from ... _ ....... -....... . 

Veitskopf, Laacher See, Germany, Leucite basalt from ............. -..... . 

Vesuvius, Leucite lava from old eruption of. .................. -- ...... . ..... / 

Videna in ~teiermark, Bastite in augite-andesite from .... . . _ ........ -..... . 

Weber grits .... ·----· ........... _ ........................................ . 

shales ..... _ .... _: . _ .. __ ............................... _ .... _ ••..... 

Page. 

17 

27,30 

32 

12 

13 

21 

23 

:37 

19 

14 

31 

34 

25 

25 

33 

13, 14 

15 

Weston's Pass, Geologic structure of ............................. __ ..... _.. 12 

Zirkel, F., on augite-andesite . . ..... ------ .. · .......... ··------- -- ...... 31,33,34,37 

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. NOTICE. 

··. The bul!~tius of the United States Geological Survey wi~ b~ numbered in ·,. cohtinllOUS series and Will be bound in Volum~s of. CO;lVenient'slze. : ~ -

.·This l}~letiu wili be included i~ Volume I. ~ :f 

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