Please do not destroy or throw away this publication. If you have no further use 

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UNITED STATES DEPA 

Secretary 

u~·u~·uu• ~a.~ SURVEY 

MeJ~eJtthalll, Direetor 

PALEOZOIC FO 

MOSQUITO RA 

ATIONS OF THE 

GE, COLORADO 

BY 

J. HAR JOHNSON 

Shorter contributions general geology, 1934-35 

15-43) 

Price 10 cents 
CONTENTS 

. Abstract _________________________________________ _ 

lntroduction _________________________________ ~----

Location and topography __________________________ _ Geology _________________ __________________ ______ _ 

General features ______________________________ _ 

Structure ____________________________ ________ _ 

Stratigraphy _____________________ ____________ _ 

Formations present _______ ________________ _ 

Cambrian system _______ __________________ _ 

Sa watch quartzite _____________________ _ 

Ordovician system ________________ ________ _ 

Manitou limestone ____________________ _ 

Harding sandstone ____________________ _ 

Fremont limestone ____________________ _ 

Devonian system ____________________ _____ ·_ 

Chaffee formation _______ .:. __________ . ___ _ 

Parting quartzite member _______ ___ _ 

Dyer dolomite member ____________ _ 

Devonian-Mississippian boundary ___________ _ 

Page 

15 

15 · 

16 

17 

17 

17 

17 

17 

19 

19 

21 

21 

22 

23 

23 

23 

23 

24 

25 

Geology-Continued . 

Stratigraphy-Contin~ed. 

Carboniferous system __ ___ _________________ _ 

Leadville limestone (Mississippian) ______ _ 

Mississippian-Pennsylvanian boundary __ _ 

Pennsylvanian-Permian sediments ______ _ General features __________________ _ 

Weber(?) formation (Pennsylvanian)_ 

Subdivisions _________________ _ Age _________________________ _ 

Relation to ore-bearing beds ____ _ Lithology ____________________ _ 

Paleontology _____ ____________ _ 

Correlation ______________ _____ _ 

Detailed sections ______________ _ 

Pennsylvanian-Permian boundary ___ _ 

Maroon formation (Pennsylvanian? 

and Permian) ____ ______________ _ 

ILLUSTRATIONS 

PLATE 1. A, Massive Sawatch quartzite near Montgomery, Colo.; B, Outcrop of Sawatch quartzite below Montgomery __ _______ ______ _ 

2. A, Shaly "red cast beds" at top of Sa watch 

quartzite near Montgomery; B, Thinbedded Manitou limestone near Montgomery; C, Medium-bedded Manitou limestone 

below Montgomery _____ __ _________ .; __ _ 

3. A, fWeber grits on South Mosquito Creek; B, 

tWeber shales on London Mountain; C, 

Manitou limestone with chert; D, Sample 

of tWeber grits ______________________ _ 

4. A, Micaceous sandstone of 1

Weber (?) formation; B, Ripple-marked sandstone of 

Weber (?) formation; C, Micaceous sandy 

shale of Weber (?) formation; D, Micaceous arkose of Weber(?) formation ____ _ 

II 

Page 

20 

20 

28 

28 

PLATE 5. A, B, Top and side views of a thin layer of 

fibrous limestone from the lower part of 

the middle Weber(?) beds ____________ _ 

6. A, Casts of salt crystals on surface of shaly 

limestone from lower part of Weber (?) 

formation near Trout Creek; B, Arkosic 

grit from upper part of Weber (?) formation in Alma district __________________ _ 

7. A, Outcrop of Fremont, Harding, and part of 

Manitou along Trout Creek near old Newett station; B, Log of silicified wood from 

the lower Pennsylvanian near Trout Creek_ 

FIGURE 2. Relations and changes in thickness of the prePennsylvanian Paleozoic formations ___ _ 

Page 

27 

27 

27 

27 

27 

28 

28 

28 

28 

28 

30 

33 

33 

42 

43 

Page 

28 

28 

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16 
PALEOZOIC FORMATIONS OF THE MOSQUITO RANGE, COLORADO 

By J. HARLAN JOHNSON 

ABSTRACT 

The Mosquito Range is a narrow, nearly straight ridge about 

SO miles long in central Colorado, separating South Park from 

the Arkansas River Valley. The higher peaks reach altitudes 

of over 14,000 feet, and very little of the region descends 

below 9,000 feet. 

The rocks of the region range in age from pre-Cambrian to 

Recent but consist mainly of pre-Cambrian granite and metamorphic rocks, and Paleozoic sediments: All are cut by 

Tertiary intrusive rocks. 

The Paleozoic sediments include deposits from every period 

except the Silurian. The Cambrian sediments form the Sa watch 

quartzite. The Ordovician includes three formations-the 

Manitou (tWhite limestone 1 of old reports), Harding; and Fremont. The Manitou consists of dolomite beds that are more 

or less siliceous. It is widespread and may be very thick. The 

Harding consists of sandstone, sandy shale, and shaly limestone, 

generally gray, green, or brown. The formation has not been 

found along the range north of Weston Pass. The Fremont 

formation consists of a gray fossiliferous dolomite. It is found 

only at the south end of the range. Pronounced unconformities 

occur at the top of the Manitou and at the top of the Fremont. 

A minor one occurs between the Harding and the Fremont. 

The fossils collected from the Pennsylvanian include 92 

species of invertebrates, of which 26 are new, and about 20 

land plants, several of which are also new. The fossils show 

that the lower antl middle parts of the Weber (?) formation are 

equivalent in age to the middle and part of the upper Pottsville 

of the East. The paper includes detailed sections ·of the 

Pennsylvanian sediments measured. 

INTRODUCTION 

From the time of the public~tion of the Leadville 

monograph 2 by the United Stat,es Geological Survey, 

in 1886, the general geology and stratigraphy of the 

Mosquito Range around the Leadville and Alma districts have been known. In the recent resurvey of the 

area, however, it has been found necessary to undertake much more detailed studies' of most of the formations. In particular, the sediments of ·Pennsylvanian 

age and the overlying red beds have' received considerable attention · and thought. This study was 

necessary to determine the ,amount of displacement 

along some of the notable faults and the depth to older 

strata that had contained valuable ore deposits in the 

larger mining districts. In some places the outcrops 

appear to have been improperly correlated in the older 

reports. These were given additional study, and considerable revision of stratigraphic sections has been 

The Devonian sediments are · widespread throughout the 

region. They consist of the Chaffee formation, which includes 

the_ Parting quartzite member below and the Dyer dolomite 

member above. The Dyer represents the lower portion of the 

Blue limestone of Emmons.· The Lead ville limestone, of Mississippian age, unconformably overlies the Chaffee formation. It 

represents the upper portion of the Blue limestone of Emmons. 

Another unconformity separates the Leadville from. the Pennsyl- necessary. 

vanian sediments above. The Pennsylvanian deposits grade up- The material on which the 'present report is based 

ward into those of the Permian. Immediately over the Leadville was collected in part by the geologists engaged in the 

limestone comes the Weber (?) formation. The lower portion · large-scale mapping of the Alma and Leadville disof this form::ttion consists mainly of black shale and sandy shale : tricts for the United States Geological Survey in 

with some interbedded sandstone and grit. Higher in the : cooperation with the Colorado ,State Geological Sursectior:t grit predominates, with some interbedded limestone, · 

shale, and sandy shale, These beds grade upward into a series ; vey Board and the Colorado Metal Mining Fund 

of red beds with interbedded limestone known as the Maroon : during the seasons of 1928-31, and by Edwin Kirk, 

formation. : of the United States Geological Survey, who collabAt the present time no definite boundary can be ;drawn . orated with these geologists during 1929. Special 

between the Pennsylvanian and Permian of this regiop, It i · . -. . 

cannot be done on the basis of lithology, for neither mideralogic ' field work co~ne:ting ~~ese observatiOns was concomposition nor grain size will serve, nor will color, for good red ; ducted by the . wnte,r dunng the field s~asons of 1930 

beds. occur within definite!! know~ Pe~msylvanian. The l?wer ] and.1931. T-~e work consisted of me~suring detailed 

beds carry abundant fossils, but fossils become progressively i sectiOns trac.mg beds .from one sectiOn to another, 

scarcer at higher ·stratigraphic levels. Evidence at. hand , and sea;ching ~r fossils The field work was followed 

suggests that the Permian-Pennsylvanian boundary is about . · · · 2,000 feet above the base of the Pennsylvanian. · by laboratory ~tudy of the rock ~~eCimens and fossils 

The lithology of the Pennsylvanian sediments is discussed ' collected, leadmg to the recogmtwn of several new 

in detail in this paper. Grit and .coarse clastic sediments form species. over 60 percent of the deposits. · They are composed almost Relatively little .detailed work had been done along 

entirely of material eroded from the pre-Cambrian rocks. the Mosquito Range except in the immediate vicinity 

I A dagger (t) preceding a geologic name indicates that the name has been aban- of Leadville and Alma. The area was studied :in 

doned or rejected for use in classification in publications of the U.S. Geological 

Survey. Quotation marks, which were formerly used to indicate abandoned or 

rejected names, are now used only in the ordinary sense. 

2 Emmons, S. F., Geology and mining industry of Leadville, Colo.: U.S.Geol. 

S_urvey Mon. 12, 1.886. 

'15 
16 SHORTER CONTRIBUTIONS TO GENERA.L GEOLOGY, 1934-35 

reconnaissance by the old Hayden Survey, 3 and the 

south end of it was touched by the Wheeler Survey.4 

z 

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z 

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:;:; 

<tl 

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Emmons/ in the Leadville monograph, gives a good 

general picture for the entire range, but his statements 

become more and more vague and inaccurate as the 

distance from Leadville increases. Irving and Loughlin,6 in their revision of the Leadville monograph, add 

much information about the ore deposits but contribute little to our knowledge of the general stratigraphy 

of the region. The discrepancies and uncertainties 

in stratigraphy that confronted these authors, however, 

had considerable to do with initiating the critical 

review of the stratigraphy in the field during the last 

few years. 

The purpose of this paper is to record the new jnformation on stratigraphy obtained by the cooperative 

work together with a summary of the older materi~~l 

so as to present a statement of our present knowledge. 

The portions dealing with the pre-Pennsylvanian 

formations are relatively brief, whereas the discussions 

of the Pennsylvanian and Peri:nian are more detailed, 

because they were the main subject of study . . 

The writer gratefully acknowledges the information 

supplied and the many courtesies extended to him by 

members of the United States Geological Survey and 

by other geologists. Q. ·D. Singewald and C. H. Behre 

aided greatly in the work around Alma and Leadville. 

T. S. Lovering aided in the area around Breckenridge. 

B. S. Butler and G. F. Loughlin contributed from 

their general kllowledge of conditions in central Colorado and _by many kind suggestions and encouragements throughout the period in which the work was 

being done. David White and G. H. Girty have 

given much help in connection with the study of fossils and their interpretations. Edwin Kirk supplied 

much of the material incorporated in the discu::;sion of 

the Devonian and Ordovician deposits. C. E. Resser, of the United States National Museum, studied 

the Cambrian fossils and suggested their correlation. 

Valuable suggestions were obtained from H. A. 

Stewart, of the Texas Production Co.; R. Clare Coffin, 

of the Midwest Refining Co.; and the late H. J. Packard, of the Contmental Oil Co. 

Many of the photographs used as illustrations of 

outcrops and field views were taken by Robert E. 

'Landon, who assisted Singewald in 1930, and photographs of specimens were taken by W. 0. Hazard, 

of the United 'States Geological Survey. 

LOCATIQN AND TOPOGRAPHY 

The Mosqillto Range is a narrow, nearly straight 

ridge about 80 miles long, trending a little west of 

north and extending from 38°20' to 39°30' north latitude and from about 105°50' to 106°8' west longitude. 

Topographically the range has a narrow crest that has 

been deeply incised by the action of alpine glaciers, 

s Peale, A. C., U.'S.Geol. and Geog. Survey Terr. Seventh Ann. Rept., for 1873, 

pp. 193-273,1874. Endlich, F. M., idem, pp. 275-361. Peale, A. C., idem for 1874, 

pp. 73-180,1875. Endlich, F. M., idem, pp.181-240. 

t Stevenson, J. J., U.S.Geol. and G!lQg. Surveys W. 1ooth Mer. Rept., vol. 3, pp. 

303-501, 1875. 

5 Emmons, S. F., op. cit., pp. 45-88. 

6 Emmons, S. F., Irving, J.D., and Loughlin, G. F., Geology and ore deposits of 

the Leadville mining district, Colo.: U.S.Geol. Survey Prof. Paper 148, 1927. 
PALEOZOIC FORMATIONS OF THE .MOSQUITO RANGE, COLORADO 17 

and as a result the crest in many places is surprisingly 

narrow, with large steep-sided cirques forming the 

heads of most of the gulches that cut into it. The 

range is bounded on the west by the valley of the Arkan-

. sas River, on the south by Trout Creek, a large tributary of the Arkansas, and on the east by South Park. 

Northward it passes into the Gore Range. The 

approxiinate northern boundary is generally taken to 

be the valley of Tenmile Creek. The highest peaks of 

the range attain altitudes of more than 14,000 feet, 

and very little of the region descends below 9.,000 feet. 

Most of the field work for the present report was 

carried on above timber line, where the intense glacial erosion has provided many splendid exposures of 

the formations. The geology along the lower slopes 

is greatly obscured by moraines and fluvioglacial 

deposits. 

The area studied includes the Leadville and Alma 

mining districts and lies close to the Kokomo, Breckenridge, ·and Red Cliff districts. 

GEOLOGY 

GENERAL FEATURES 

STRUCTURE 

Structurally the region consists of several · asymmetric folds that have been cut by large reverse faults. 

In gene~al, the regional dip is toward the east, though 

locally there are sharp and steep reversals, which 

usually indicate the proximity of important faults. 

These folds and faults were formed after the intrusion 

of most of th~ porphyry sills but before the intrusion 

of the larger ~ertiary stocks and batholithic masses of 

monzonitic rock. Still later there was normal block 

faulting. l 

The struct 1 e is most complex at the north end of 

. the range, in lthe Leadville-Alma region. According 

to Emmons 7 • t becomes simpler to the . south. The 

individual fol s gradually merge or die out until south 

of the Buffalo Peaks the main range appears to consist 

of ~mly one fo d somewhat faulted. 

STRATIGRAPHY 

FORMATIONS PRESENT 

The Paleoz ic rocks of the Mosquito Range include 

deposits from very period except. the Silurian. There 

ar.e, however, ~evera1 unconformities within the section, 

some of whicf represent long intervals of time for 

The rocks of the region range in age from pre- which deposits are lacking. · 

Cambrian to Recent but consist mainly of pre-Cam- The table bFlow shows the formations present and 

brian granite, Paleozoic sediments, and Tertiary dikes, gives a summary of their characteristics; the two 

sills, and stocklike masses. The subjoined table will tables followihg it give the thickness of the pregive a general idea of the character of the formations. PennsylvaniaJ formations obtained in a number of 

The Buffalo Peaks form a picturesque and con- measured sec, ons. Figure 2 shows graphically the 

spicuous pair of prominences south of Weston Pass. relations and ahanges in thickness of the pre-PennsylThey represent a center of Tertiary extrusive activity vanian formations. 

which is noteworthy in the geology of South Park but 7 Emmons, s. F., ntroductory geological sketch of Buffalo Peaks, Mosquito 

not in that of the Mosquito Range. Range, colo.: u.s. Geol. Survey Bull. 1, p. 12, 1883. 

General stratigraphic column of the Mosquito RJnge, Colo. 

~ Age Formation 

Pleistocene. 

Unconformity 

Tertia!Y· 

Unconformity 

Permian and Pennsylvanian (?). Maroon formation. 

Pennsylvanian. Weber (?) formation. 

-Unconformity 

Thickness 

(feet) 

2, 000± 

1, 100± 

550+ 

5(}-300+ 

l 

Lithologic character 

Gravel and silt. 

Silt and vo canic rocks. Some extrusive rocks in southern 

part of area. Sills are commo.n, espec~ally a~ nort~ end, 

and gen rally occur at certam stratigraphic horizons, especiall~ at or near base of Weber (?) forma,tion. 

Red sandst 1 

ne and sandy shale, commonly micaceous and 

arkosic. A few lenticular beds of limestone and gypsum 

in lower ortion. 

Sandstone nd grit "":ith som~ interbedded li~estone. MaterialJ v:ery arkosic and miCaceous. Color m lower 

part ligh~ to dark gray. Grades upward into red beds. 

Gray sandst one and grit, with interbedded limestone and 

shale. ~ecomes more and more arkosic and micaceous 

toward t(!)p. The beds tend to be lenticular and non- persistent. I 

Black carbdnaceous shale, commonly very sandy. Locally a thin bapal sandstone or conglomerate. 
18 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1934-35 

General stratigraphic column of the Mosquito Range, Colo.-Continued 

Age Formation Thickness Lithologic character (feet) 

Dolomite, blue to lead-gray, some beds almost black. 

Beds massive to thin. Contain shale in places or even 

Mississippian. Leadville limestone. 50-300 sandy streaks. Chert nodules and streaks are locally 

abundant. Sandstone at base, a few inches to 12. feet 

thick, accompanied by dolomitic breccia. Is upper part 

; Unconformity 

of tBlue limestone of early reports. 

d Gray dolomitic limestone, mainly dark gray but locally 

becoming lighter at the base. Tends to weather brown 0 

:j3 Dyer dolomite mein- 75 or tan. Locally contains sandy and shaly layers, espe- ~ ber. cial1y toward the base. Is lower part of tBlue limestone s of early reports. Upper Devonian. 0 ""' ..... 

<l) White or nearly white sandstone and sandy shale. Largely .. <l) 

~ quartzitic in the Leadville region. Some layers of Parting quartzite ~ o-70 poorly rounded pebbles. · Weathers pink to red-brown. ..c:: member . 0 Locally contains red and green shale and calcareous 

shale, especially at the base. 

Upper Ordovician. Unconformity 

Fremont limestone. 0-75 Massive white to dark-gray dolomitic limestone. 

Middle Ordovician. Harding sandstone. Q-50 Chiefly sandstone and quartzite, with some calcareous 

shale and impure limestone, gray, green, and reddish 

brown. 

Lower Ordovician .. Thin-bedded light gray dolomitic limestone, very siliceous 

Manitpu limestone. 18-250 in places. Contains interbedded shale. The t White 

limestone of Leadville district. 

Shale, thin limestone, and shaly limestone, some sand-

..c::o.i Peerless shale mem- 4Q-60 stone . Upper Cambrian. Q:e ber. Includes "transition beds." In places some of the lower ;..;>~ 

~;..;> tWhite limestone of old reports has not been separated. ~~ i::=""' 

w.::l 0" Thin to massively bedded quartzite, gray to white. 0-190 

-Unconformity Locally a basal conglomerate. 

Pre-Cambrian. Gneiss, schist, and. granite. All cut by pegmatite and 

aplite dikes. 

Thicknesses of pre-Pennsyl~anian sediments (feet) 

Alma district a 

. . . 

.l:d· <D "' ~ 

~ '0 ~ ~ 0 ~,... c.>S <D ::l ·a ;s.c:l ~~ ::lo ::l ~ ... I=Q3, 0 a; I=Q,.c:l <D 

;s _ .... ~ bll '0~ § o& 'O.c:l '0~ 0~ 0 .s <D .g <Do .a .;,~ C) ,.c:l.c:l ... ~ C) 

..b:l ~'3 ~~ :;;E ~·.-< C) .s ~;@ '3 .... ~ 

0 

~ ~.e •;JC!:i~ ro+> H 

~ "'·.-< ~~ c;; 

:5& 0 . g p. .c:l~:;:: :5~ <D C) IZIO :5 ~ :;;;;;~ !S<tl ~ ::l ::l ~ ~I=Q !:> !:> 0 0 0 ;s o"'~ 5 p:; . ~ ro ro z z ;s ---------------------

Leadville limestone. 

cD Limestone _____________ 135 ------ ---- ____ ... 85+ ~ 

0 . 120± 

---- ---- ;..;> 

. I i · r:ll 

. .. <l) Quartzite zone __ ,; _______ 2± 5 8max. 5max. ] ---- ----- 135 ----50±1--

<l) Dyer dolo- ::l 65 40 40± ~ mitemem- +- ber. 

.Chaffee formation. -------------------- Parting quartz- 38 55 1{> 45 35 30 10 10 Ab-

'. . ite member. sent 

Upper limestone zone. I Ab- 140 55± 115± 80 sen t 

Manitou limestone --------- -- --

(t White limestone). Shale zone. 50 110(?) 180 24 15 110± 14 85 16 

-------- -- ---

Lower limestone zone. I 20 20 15± 28 

a Singewald, Q. D., and Butler, B. 8., Preliminary geologic map of the Alma mining district, Colorado: Colorado Sci. Soc. Proc.; vol. 12, pp. 295-308, 1930; Preliminary report on the geology of Mount Lincoln and Russia mine, Park County, Colo.: Idem, pp. 389-406, 1931. 
PALEOZOIC FORMATIONS OF THE MOSQUITO RANGE, COLORADO 19 

Thicknesses of pre-Pennsylvanian sediments (feet)-Continued 

~ ,;, l=l 

~~ ~ 'd ~ l=l Q) 

0 <e....._ 0 ~ ::s "§ ~..c:t ..c:ta:> ::s 0 

<il o,;<;::: ::So ~ .... 

bl) ~ -~ l=l .... ~ ~'-" d~ .E! - l=l o::s l=l •.• ..c:t '0-§ ..c:t 0 00. oo Q) 

:r;; ~o .a ..c:t..c:t 0 ~ 0 

¢El a:>'3 l=l 0 :Eo 0 ....,0 ~'3 ~:=: '3 ~ ~ ..,o :5lo......_ "ii.i0 o..c:t 0 00+01 ~ rn~ o'"" "' Q) cnO. 

~ .c:::S 0 oP. ..c:tl=l~ :S~ enS 2$ ..c:t -= 0 .._,0' ~ cnO ~:r;;~ . !J:l< · ~ t! ::s 0 ::s al ce~ o"'o. ~"' 0 

~ 0 ~ ~ 5 p:; 0 ;:g CQ CQ z z ------------------------

Limestone shale Shaly zone. 26 27 25 

Peerless shale ("transition 50 30± member. --- 65 ----- 30± 32± 35± -- shale"). Limy zone. 20 23 20 

------ ~ 

~ Purple quartzite zone. 3 10 2 13 ~1 7 ~ 

'"' --- a;j ------ ;:! 

0" Upper quartzite zone. 10 ' 6 13 8 10 10 ~ 1:) ----- ------ ------ +" 

a;j Thin-bedded limy zone. 12 130± 12 13 ~ 90± 19 11 9 a;j 

U1 . ------ ------

Lower quartzite zone 90 92 40± 76 80± 

(including basal con- glomerate). 

West side of Mosquito Range b 

Weber (?) formation. 

Leadville limestone. 

cP, 

~a;j~ Dyer dolomite member. 

a;j ~.s ~o-+" 

o- Parting quartzite member. 

Manitou limestone (tWhite limestone). 

A ~ I Peerless shale member ("transition shale"). ~.Et:-2 U1 a;j a;j ..... 

~;:::! 0" 

Pre-Cambrian. 

' 

b Supplied by C. H. Behre. 

CAMBRIAN SYSTEM 

SA WATCH QUARTZITE 

. 

Subdivisions.-The Sawatch quartzite as identified 

in this region contains at the top about 50 feet of shale 

and calcareous deposits which in previous reports have 

been called "transition shales" and "red cast beds" 

but which are here designated "Peerless shale member 

of Sawatch quartzite." It is not known whether the 

Peerless member can be discriminated over wide areas 

or whether it is in some areas replaced by quartzite. 

According to Resser,8 the few fossils that have been 

found in the quartzites suggest a fauna distinctly 

different from those found in the shales. Behre 9 

s Resser, C. E., personal communication, February 1931. 

g Behre, C. H., Jr., The Weston Pass mining district, Lake and Park Counties, 

Colo.: Colorado Sci. Soc. Proc., vol. 13, p. 58, 1932. 

Mount West Sherman West slope of Zion Dyer Moun- Head of Empire · Horseshoe Weston 

(com- Moun- tain Amphitheater Mountain ·Pass 

posite) tain 

---

Erod-· (?) 

ed. 

145. 5 60 126. 5 Top not ex- Top not ex- 300 posed. posed . .' 

95.5 78 8.7. 5 76 75 70 

33. 5 21.0 19 38 60 62 

115. 5 93 94 110 150 100 

44 49 45 55 60 50 

125. 5 63 106.5 ' 112 120 100 

suggested the use of the term "Peerless member" 

for the argillaceous and calcareous upper portion of 

the Sawatch. He subdivides the Cambrian sediments 

of the Leadville district thus: 

Sawatch quartzite: . . ·.··· 

Peerless shale member ("transition shale" of older reports): 

Alternating calcareous and shaly layers, thin-bedded. 

Near top "red cast beds" are numerous. (See pl. 

44, A.) 

White, fairly pure, well-cemented quartzite,. with a · dark 

bed at the top. Base conglomeratic. Some beds near 

top shaly. 

Singewald has subdivided the Sawa~ch in the Alma 

district as follows: 

Limestone-shale member ("transition shale"): 

Upper shaly zone . . 

Limy zone. 
20 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1934-35 

Pu,rple quartzite zone. 

Upper quartzite zone. 

Thin-bedded limy zone. 

Lower quartzite zone (including basal conglomerate). 

General jeatures.---:-The Sawatch quartzite CtLower 

quartzite of Emmons) lies directly upon the eroded 

surface of the pre-Cambrian rocks. The contact with 

the underlying rocks is a rem·arkably smooth surface 

and is well described by Irving and Loughlin.10 Generally the formation consists of hard, mas~ively 

bedded grayish-white quartzite. (See pl. 1, A, B.) 

Locally there are thlli basal conglomerate beds compos~d of well-rounded and polished grains of bluishgray quartz, commonly about the size of a pea, well 

cemented· by a siliceous cement. 

The Sawatch quartzite is a cliff maker and is readily 

recognized along the canyon and cirque walls. 

Thickness.-The quartzite differs considerably. in 

thickness in different localities. Near Tro.ut Creek it 

is absent or very thin. At Weston Pass about 60 feet 

of it appears to be p.resent, a.nd in the Leadville and 

. Alma districts a maximum of 120 to 130 feet is attained. 

Age.~Only a very few fossils have been collected 

from the formation----:-none during recent years. Emmons 11 reported a few from Monte Cristo Gulch, 

north of Hoosier Pass. Their exact stratigraphic 

position could not be determined, but he believed it to 

be near the · base of the transition shales. Such 

meager information as has been obtained onadjoining 

areas points to an Upper Cambrian age, probably 

middle Upper Cambrian, and the formation has for 

many years been classified as Upper Cambrian. 

Peerless shale member.-Behre 12 introduced the 

name "Peerless shale member", taking the Peerless 

-mine on Sheridan Mountain, about 7 miles southeast 

of Leadville, as . the type locality. The beds consist 

of thin-bedded shale, calcareous shale, and calcareous 

sandstone. The contact with the underlying quartzite is sharply defined in some places and gradational 

in others. In general it seems to be marked by the 

top of a black or dark-brown quartzitic layer. The 

contact with the overlying Manitou Hmestone is not 

well defined, as there is a gradual transition upward 

into the limestone series. The so-called "red cast 

beds" are usually considered to constitute the top of 

the Peerless member. These consist of a sandy limestone, nearly white where fresh, which contains numerous flat pebbles of .dark red, suggesting cast of fossils · 

on a broken or weathered surface. They are present 

· in most of the Leadville and Alma districts but are 

·absent at a few localities. 

The colors of the Peerless sediments show considerable variety. The lower beds are usually gray or 

greenish gray. The upper layers may be gray, buff, 

10 Emmons, S. F., Irving, J. D., and Loughlin, G. F., U.S.Geol. Survey Prof .. 

Paper 148, p. 25, 1927. 

11 Emmonll, S. F., Geology and mining industry of Leadville, Colo.: U.S.Geol. 

Survey Mon. 12, p. 60, 1886. 

12 Behre, C. H., Jr., Colorado Sci. Soc. Proc., vol. 14, p. 58, 1932. 

·brown or even brick-red, the reddish shades being ' . most conspicuous~ All the measured sectwns of the 

Peerless member used in this report were obtained in 

the Leadville and Alma districts. They show thicknesses ranging fron1 23 to 60 feet. The beds t~in to 

the east and south of those districts, and thicken to 

the west and northwest. 

A moderate number of fossils have been collected 

from some of the upper layers of the Peerless member. 

Butler arid Singewald, collected from several localities 

in the Gilman and Alma districts, and the present 

writer from others. Practically all the collections 

represent the same stratigraphic horizon. C. E. 

Resser examined the fossils and reported that, with a 

few exceptions, they are undescribed species of trilobites and brachiopods. The trilobites belong to the 

genera Tellerina, Saukia, and Briscoia of the family 

Dikellocephalidae, and · the brachiopods are of the 

Lingulella or Westonia type.· Billingsella coloradoensis 

was obtained from the lower shales near Leadville. 

The age indicated is middle to late Upper Cambrian . 

Detailed sections.-Detailed sections of the Sawatch 

formation, measured by C. H. Behre, Jr., are given 

below. · 

Section of Sawatch quartzite on Sherman Mountain, Iowa 

Amphitheater, near Leadville, Colo. 

Peerless shale member: 

Pinkish sandy limestone or caicareous sandstone, in 

beds 2 to 3 feet thick. Shows irregular ironstained partings suggesting cross-bedding. General colors highly variable-brick-red to oliveFeet 

gray or buff ___________________ -_------------ 16 

Thin-bedded shaly sandstone, notably banded with 

iron oxide___________________________________ 7 

Thin-bedded fissile shaly sandstone; light . olive-

• . green when fresh, weathering to deep buff or 

brown. A few quartzitic layers as much as 1 

foot thick _____________ ----------------------_:..:__ 

Total thickness of Peerless membe~ ______ ---- 45 

Massive conglomeratic quartzite, weathering to a buff 

color but yellowish-gray when fresh. Subangular 

quartz grains, irregularly cross-bedded. Sand grains 

weather out on the surface _______________________ _ 

. Impure, arkosic and micaceous pinkish quartzitic sandstone, weathering gray __ -_-_----------------------

White massive quartzite, very dense; weathering pinkish. 

Beds 1 to 4 feet thick; a few thin, shaly layers in places_ 

Buff and white, streaky dense quartzite in beds as much 

as 6 inches thick ___________ -----------------~----

Dense, very massive white quartzite _________________ _ 

White quartzite ___ ~ ____ -- ____ ----------------------

Massive white quartzite with local sandy-weathering 

brownish beds ___ --------------------------------

Massive white quartzite ______ ----------------------

Massive, dense quartzite, weathering white to pink, very pure ___________________________________________ _ 

Massive white quartzite, weathering buff-------------

White thinner-bedded quartzite, weathering gray or buff; 

individual beds 2 feet or less thick ________________ _ 

10.5 

6 

9. 5 

6. 5 

6 

2 

22. 5 

10 

14 

5 

14. 5 

106. 5 

Total thickness•of formation ________________ 151. 5 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 185 PLATE 1 

A. MASSIVE SAWATCH QUARTZITE NEAR MONTGOMERY, COLO. 

B. OUTCROP OF SAWATCH QUARTZITE BELOW MONTGOMERY. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 185 PLATE 2 

A. SHALY "RED-CAST BEDS" AT TOP OF SAWATCH QUARTZITE NEAR MONTGOMERY, COLO. 

B. THIN-BEDDED MANITOU LIMESTONE NEAR MONTGOMERY. C. MEDIUM-BEDDED MANITOU LIMESTONE BELOW MONTGOMERY. 
PALEOZOIC FORMATIONS OF THE MOSQUITO RANGE, COJ.ORADO 21 

Section of Sawatch quartzite on east slope of West Dyer Mountain 

Peerless shale member: Feet 

Pinkish sandy limestone in thin, shaly layers, with 

irregular bedding planes. Beds as much as 1 foot 

thick but generally only half an inch____________ 19 

Shaly, slabby impure sandstone. Some greenish 

and rarer brick-red shaly beds~---------------- 11 

Impure micaceoua sandstone, weathering a rusty 

brown, in beds 1 foot or less thick, with ;,;ha1y 

partings 3 inches thick; shows irregular crossbedding________________ ___________ _____ _____ 19 

Total thickness of Peerless member_ _ _ _ _ _ _ _ _ _ 49 

Pinkish quartzite in a single bed; weathers dark brown_ 2 

Alternate beds of calcareous shale bearing sand and 

quartzitic beds, all weathering buff; beds 1 foot thick__ 5 

White massive qu~rtzite in beds 2 to 10 feet thick ____ -. '56 

63 

Total thickness of formation__ __________ _____ 112 

Probable top of pre-Cambrian. 

Section of Sawatch quartzite on south slope of Mount Zion 

Peerless shale member: Covered, probably represents Feet 

shale, as slope is distinctly gentler _________ ____ ____ ·_ 44 

White, very pure quartzite, alternating with commonly 

discontinuous sandy layers that lack induration and 

_weather buff__ __________________________________ 36 

White, ,very pure massive quartzite______ ___ _________ 24 

White coarse-grained quartzite, in beds as much as 18 

inches thick, with separating laminae of · micaceous 

shaly quartzite 1 to 2 inches thick____ __ ___________ 54 

White, pure quartzite, weathering with purplish blotches 

in grayish or buff colors. Irregularly cross-bedded_ 5. 5 

Fine-grained conglomerate in beds as much as 6 inches 

thick_____________________________ ___ ___________ 6 

125. 5 

Total thickness of formation ___________ ..:_ ____ 169. 5 

ORDOVICIAN SYSTEM 

·MANITOU LIMESTONE 

Correlation.-+n the revised Leadville report 13 the 

rocks designated by Emmons t" White limestone" and 

"Parting quartzite" were put together under the term 

t" Yule limestone" and were referred to as the 

t"White" limestone member and the "Parting" 

quartzite member. This treatment, for want of satisfactory data, was in accordance with the old assumption that they corresponded to the Yule limestone of 

the Anthracite-Crested Butte and other areas of central Colorado . . Recent work by Kirk and others 

shows that the term t"Yule" has been applied to 

limestones that range in age from Upper Cambrian 

to Mississippian in different districts, and that the 1 

material at the type locality on Yule Creek inay be of 

Carboniferous age. At the · sai:ne time the work of 

Behre, Singewald, Kirk, and others . in the Mosquito 

l$ U.S.Geol. Survey Prof. Paper 148, p. 27, 1927. 

58869--34-2 

' ·Range shows that the tWhite limestone and Parting. 

quartzite are separated by an unconformity at their 

type locality. At the south end of the Mosquito 

Range the Harding and Fremont formations lie between 

them. The tWhite limestone is Ordovician and has 

been correlated with the Manitou limestone by Kirk. 

The term "Manitou" has long been used for the Lower 

Ordovician rocks of similar age and lithology in adjoining-regions, so that it seems logical to apply that term 

to the beds in this area rather than to coin a new na~e·; 

The Parting quartzite, as shown below, is Devonian/· 

and it is therefore not t;tdvisable either to consider th~I; 

Parting quartzite and tWhite limestone as parts o{

one formation or to apply the term t" Yule" to eith~~' 

or both. Kirk has given the name "Chaffee format;· 

tion" to the Devonian rocks of central Colo'rado, 

including the Parting quartzite and the Dev~nian_·\ 

portion of the tBlue limestone of early reports. . " 

Character.-The Manitou formation consists of thin-· 

bedded dolomitic limestone (much of it highly ~iliceous), in many places with thin shaly layers. . (See 

pl. 2, B, C.) It becomes increasingly shaly toward. the 

top. The shales are dark green to dark gray or al:fu.ost 

black. The amount of shale differs in different 

sections. 

The limestones are highly crystalline and gener.ally . 

white or light gray. The beds are in few places over 

4 or · 5 inches thick and in many places are separa,te.d 

by partings of shale. This is almost everywhere true 

in the Leadville-Alma region, but at the south end';. of 

the range the formation thickens and the proport~on 

of limestone become$ greater. 

At certain horizons there are concretions and seall!s 

of white or cream-colored chert or chalcedony. (-$~!3 i 

pl. 3, 0.) The chert remains unaltered by weathering{ 

or by mineralization or replacement of the rock. Oil' 

weathered surfaces it may form conspicuous ribbin~ 

and other irregular~ties. Similar surface marki~gs 

may be caused by .the presence of irregular leri§~s 

mostly arranged parallel to the stratification, in wh}ph 

silica is more ahtmrlft!lt than in the body of the to<.(~;;.·. -·· 

as noted by Patton 14 and by Loughlin. 15 · ·"·"· 

Thickness.-The thickness of the formation varies 

considerably even within short distances. In the 

Leadville area it averages about 120 feet. In the 

Alma district, to the east and northeast, measurements were obtained that showed a minimum of 44 

feet and a maximum of 190 feet. At the south end of 

the range the thickness increases until at Trout Creek, · 

in a measured section, it amounts to nearly 400 feet. 

Pre-Devonian erosion undoubtedly caused most of 'the 

variations in thickness. 

Age.-Emnwns considered the tWhite limestone to 

be Silurian, the term "Ordovician" not then being 

u Patton, H. B., Geology and ore deposits of the Alma district, Park County, 

Colo.: Colorado Geol. Survey BulL 3, p. 51, 191~ . . . . 

15 Emmons, S. F., Irving, J.D., and Loughlin, G. F ., Geology and ore deposits of 

the Leadville mining d~trict, Colo,: U.S.Geol; Survey Pcof. Paper 148, p, 28, 1927. 
22 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1934-35 

used by the ·Geological Survey· as a period name. For 

the .cotrelatioh he had practically no paleontologic 

evidi:mce .. · Later work has accumulated more information, 'so that Loughlin," in 1927, was able to state that 

the formation is unquestionably of Ordovician age. 

The fossils reported from ·it include cystid fragments, 

Dalmanella melita,. Orth-isina aff. 0. pepinensis, Eoorthis 

ochusaj Syntrophia sp., Piloceras sp., Colpoceras sp., 

Ophileta. cf. 0. ·trohiscus, . and fragments of trilobites 

and gastrop.ods. Most of these identifications are old 

and may not be very accurate, but abundant fossils 

have been obtained. from the formation in adjoining 

dist~~cts, so that the. age can be definitely stated as 

Lower Ordovician. 

Detailed s·ections.-Sections of the Manitou, measured by- C. H. Behre, Jr., are given below to show its 

charicter in detail. 

Section of .M imitou limestone from south slope of Mount Zion 

Concealed _____ _______ ________ ____ __ ______ ______ __ _ 

Tliin"-bedded ve~y light pinkish shaly li:J;nestone; weathering almost white. Texture sugary _______ ____ _____ _ 

Light-gray granular limestone, weathering almost white. 

Upper part in beds as much as 6 inches thick and 

banded with silica on weathered surface. Fracture 

distinctly platy. A few thin beds of shale interbedded in lower part, of which limy layers are like the 

preceding _____________ ____ ________ :.. ____ · ______ __ _ 

Blue-gray, : buff-weathering · limestone, granular on 

weathered surface. Beds 2.5 feet thick, separated by 

2-inc:P, layers of green shale; sandy layers rarely present_ ----- ------------- ------------- --------- C~ve~~<f; · probably li~estone __ ___________ ______ ___ _ _ 

Pink crystalline, slightly quartzitic 'limestone, in beds 

as much as 1 foot thick ____________ _____ ____ ___ __ _ 

Section of Manitou limestone in Iowa Amphitheater 

Light-colore,d, buff,weathering limestone of saccharoidal 

texture, with thin layers of white chert. In beds as 

much ~s 3feet thick, ~ each of which includes several 

cherty bands- -- -------~---------- -- ---------- --

Like the last but more thin-bedded; siliceous coating on exposed -surfaces __ ________________ ___________ __ _ 

Feet 

5. 5 

10 

57. 5 

14. 5 

12 

16 

115. 5 

Feet 

29 

65 

94 

Section ~f Manitou lime~ tone from east slope of Dyer Mountain, 

near Leadville, Colo; 

~ .. , Feet 

Prominent buff-weathering beds of coarse-grained dolo- mit~- _______ - _____ - _- ________ .:___________ ___ __ __ 6 

Blocky~ locally siliceous light-gray limestone; weathers 

buff _____ ~-------~----~ ----------------------- 68 

Pinkish, sandy ·limestone, weathering to massive buff ·' beds __ . __ · _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 19 

93 

HARDING SANDSTONE 

'At the south end of the range two formations, the 

Harding· and the Fremont, occur between the Manitou 

limestone and .. the Parting quartzite, which immediately' overlies the Manitou in the Leadville area. 

General jeatures.-·The Harding formation, as developed along Trout Creek, consists of a series of alternating beds of shale and calcareous sandstone with a 

few beds of impure limestone and quartzitic sandstone. 

The individual beds are general~y rather thin. The 

color ranges from light greenish gray to dark reddish 

brown. Fragn1ents of fish plates such as characterize 

the Harding at its type locality, near Canon City, 

Colo., were found in considerable numbers at the 

locality on Trout Creek. No definite outcrops of 

this fdrmation were observed north of the Buffalo 

Peaks, although the presence of a sn1all amount of it is 

suggested at ·weston pass by the · occurrence of some 

greenish shale and mottled sandstone containing fragments of fish plates, which, however, may belong to 

the bllsal Parting. The following section shows the 

character of the Harding formation at Trout Creek. 

(See pl. 7, A.) 

Section of Harding sandstone along Trout Creek 

[Measured on north side of creek near the old railroad water tank at the abandoned 

station of Newett, in Tps. 13-14 S., R. 77 W.] . 

Contact with Fremont limestone appears regular. 

Harding sandstone: - Feet 

Sandstone. Rich green where . fresh but weathering 

to a dark reddish brown. Suggests glauconite, 

but a microscopic examination does not confirm 

this suggestion. Contains abundant worm borings or small fucoid casts..:. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2. 2 

Sandstone, white, fine-grained. A thin layer 8 

feet above base contains abundant worm borings 

and fucoid casts. Also fish plates_ _ _ _ _ _ _ _ _ _ _ 9. 3 

Sandy limestone, gray; becomes greenish gray at 

top. Massively bedded at base; platy at top____ 2. 0 

Hard gray sandstone, fine-grained. Suggestions of 

shale on the bedding planes__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3. 5 

Sandy limestone, light greenish gray____________ . 7 

Quartzitic sandstone, gray_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1. 0 

Sandy limestone, light greenish gray___ _ ________ . 7 

Quartzitic sandstone, gray-brown______________ 1. 2 

Sandy limestone, light greenish gray______ _ _ _ _ _ _ 2. 8 

Quartzite, white, thin-bedded_________________ 10. 5 

Quartzite, light gray, almost white, massively bedded ________________________________ 19.0 

Contact with Manitou limestone regular. 

Thickness.-At Trout Creek about 50 feet of the 

Harding was observed. It thickens southward, about 

7 5 feet being found on the Arkansas River below 

Salida. North of Trout Creek it thins rapidly and 

is absent north of Weston Pass. This northward 

thinning was caused, at least in part, by erosion before 

the deposition of the Parting quartzite and possibly 

before the deposition of the Fremo:n,t. Kirk 16 in a . 

recent publication discusses the distribution and characteristics of this formation in areas beyond that here 

considered. 

Age and correlation.-The only definitely recognizable fossils obtained in this area are fish plates of the 

types described by Walcott as Dictyorhabis . priscus, 

16 Kirk, Edwin, The Harding sandstone of Colorado: Am. Jour. Sci., 5th ser.,vol. 

20, pp. 456-466, 1930. 
PALEOZOIC FORMATIONS OF THE MOSQUITO RANGE, COLORADO 23 

Astraspis desiderata, Eriptychi.us american us, and 

several others. .Kirk 17 summarizes the information 

on the subject and states that the formation is undoubtedly Ordovician, 9f about late Black River or early 

Trenton age, both of which are Middle Ordovician. 

FREMONT LIMESTONE 

General features.-Overlying the Harding sandstone 

along Trout Creek is a thick, massively bedded dolomitic limestone identified as the Fremont limestone. 

The color is light gray or light brown, but on weathered 

surfaces it becomes gray to ~ark gray. Usually the 

material is highly dolomitized. , ;fhe fonp~tjon. is i" 

cliff maker and ·as such can often be recognized 

topographically. 

Distribution and thickness·.-The formation rapidly 

thins out to the north of Trout Creek and was not 

observed at Weston Pass. To the west, south and 

southeast, however, it is well developed, good outcrops 

being found near Salida, around Monarch, and in the 

Canon City quadrangle. It is about 7 5 feet thick at 

Trout Creek. · 

Age and correlation.-The Fremont is rich in fossils, 

though they are hard to collect on account of the 

character of the rock. Corals are especially common, 

but brachiopods are not rare. The following forms · 

are known from this district: Receptaculites sp., Streptelasma sp., Paleophyllum thomi, Calapoecia sp., 

Paleofavosites sp., Halysites gracilis, Rhynchotrema 

capax, and Dinorthis subq1.tadrata. The forms not 

n&med specifically are mostly undescribed species. 

According to Kirk, 18 the Fremont is approximately 

equivalent to the .. Montoya limestone of Texas and 

New Mexico and the Bighorn dolomite of Wyoming, 

both of Upper Ordovician age. 

DEVONIAN SYSTEM 

CHAFFEE FORMATION 

· One result of the recent work has been to demonstrate the existence and widespread distribution of 

Devonian rocks in central Colorado. Girty 19 suggested their probable existence in 1903. Field work 

by Behre/0 Kirk, 21 and the writer has supplied detailed 

evidence as to their presence and character. Kirk in 

his paper gives a summary of the Devonian of Colorado 

and supplies the term '' Chafi'ee formation" for the 

sediments of Devonian age found in the Mosquito 

Range and adjoining areas. The formation has two 

members, the Parting quartzite member below and 

the Dyer dolomite member above. The Parting 

quartzite member corresponds to the Parting quartzite 

11 Kirk, Edwin, op. cit., pp. 463-465. 

ts Kirk, Edwin, personal communication. 

t~ Girty, G. H ., The Carboniferous formations and faunas of Colorado: U.S.Geol. 

Survey Prof. Paper· 16, p. 162, 1903. 

2~ · Behre, C. H., Jr., Revision of structure and stratigraphy in the Mosquito Range 

and the Leadville district, Colo.: Colorado Sci. Soc. Proc., vol. 12, pp. 37-57, 1929. 

2t Kirk, Edwin, The Devonian of Colorado: Am. Jour. Sci., 5th ser., val. 22, 

pp. 222-240, 1931. 

of Emmons. The Dyer dolomite member is the lower · 

part of the t Blue limestone of Emmons and others. · 

• PARTING QUARTZITE MEMBER 

Occurrence.-In the Leadville district a comparatively thin quartzite occurs above the Manitou 

·ctWhite) limestone and below the tBlue limestone~ 

Emmons called it the "Pt;trting quartzite" because it 

separated the two limestones. Its persistence around 

Leadville has made it a valuable horizon marker, 

especially for determining the amount of displacement 

al n~ au~ts, and it is well known to the mining .fraternity. Its name has therefore re9~ntly been given a 

geographic significance, 22 'by applying the name 

"·Parting Spur" to the spur that extends from Dyer 

Mountain northwestward toward West Dyer Moun-: 

tain. This spur is now considered the type locality 

of the Parting quartzite. 

General features.-The Parting normally occurs as a 

rather .thick bedded quartzite, which, however, c~~­

tains shale partings or layers. Locally considerable 

shale occurs in it. In places there are alternations of 

thin beds of quartzite, limestone, and shale, particularly near the top or base of the member. At Trout 

Creek the total thickness of shale equals that of quartzite. The basal shale beds are commonly red. . 

A basal conglomerate was noted in several localities, 

and some streaks of poorly rounded pebbles were 

observed, both within the Leadville district and near 

. Trout Creek. In the Leadville-Alma region the 

original sandstone beds have been altered to quartzite, 

but farther south some beds of soft and friable . 

sandstone occur. 

Loughlin 23 gives the following petrographic description of the material as studied in the Leadville district; 

The quartzite layers consist of grains of bluish-white quartz · 

which range from 0.25 to 5 millimeters in diameter and average 

about 0.5 millimeter. In places large pebbles of. quartz are 

present. Component quartz particles are seen under the 

microscope to consist of more or less well-rounded grains 

erilarged by the addition of interstitial silica. It is usually very 

difficult to detect the boundary between the newly added 

quartz and the original grain, but the addition of cementing 

material has impart_ed to the grains an interlocking character. 

In the less pure beds the matrix consist:;; partly or wholly- of 

carbonates and aluminum silicates. The original quartz grains 

are filled with a great profusion of indeterminable minute 

inclusions and are presumably derived from the pre-Cambrian 

granite and related rocks that consituted the land surface from . 

which the material was derived. Inclusions of muscovite and 

minute rutile needles are present locally i:p. ,the quartz grains . . 

Thickness.-The Parting quartzite member shows 

a considerable range of thickness, even within short 

distances. Loughlin 24 shows thicknesses ranging from 

10 to 70 feet around Leadville. In the Alma district 

22 Kirk, Edwin, Am. Jour. Sci., 5th ser., vol. 22, p. 228, 1931. 

23 Emmons. S. F., Irving, J.D., and Loughlin, G. F., op. cit., pp. 3Q-31. 

2f Idem, p. 30, diagram on p. 31, and pl. 29. 
24 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1934-35 

Sing_ewald obtained thicknesses as much as 55 feet 

though the member is completely absent in at leasf 

one locality. A little over 60 feet of beds were found 

in the Trout Creek section. 

Age and correlation.-Emmons put the Parting 

quartzite into the Silurian. Loughlin 25 .reviewed the 

evidence available in 1926 bearing on the age and 

tentatively classified it as Ordovician. 

Kirk 26 presents considerable evidence to show that 

the Parting quartzite is of Devonian age. He does 

this partly on the basis of close lithologic agreement 

with known Devonian beds found short distances east 

west, and south of the Mosquito Range and partl; 

from:·· the general stratigraphic succession in central 

Colori~do. 

The field work connected with the present report 

demonstrated the existence of an unconformity at the 

base of the Parting. The fact that at Leadville the 

Parting rests upon the Manitou (tWhite) lirnestone, 

wherea.s at Trout Creek the Fremont and Harding 

formatiOns occur between then1, is in itself evidence of 

such an unconformity. In any case it seems more 

logical now to group the Parting with the lower part of 

the confonnably overlying t Blue limestone, as a member of the Chaffee formation, rather than with the 

unconformably underlying Manitou (tWhite) limestone. Field work on the west side of the Holy Cross 

and Sawatch uplifts disclosed sections where transitional gradations from Parting type of sediment to 

t Blue type occurs. For these reasons the present 

writer believes that the Parting should be considered 

Devonian rather than Ordovician. 

Well-preserved fish plates of Devonian type were 

found by the writer during the field season of 1934 

near the base of the Chaffee formation about 16 miles 

northeast of Salida. 

. J)etailed sections.-The following sections, measured 

by C. H. Behre, Jr., will give an idea of the character 

of the Parting member: 

Section .of Parting quartzite member of the Chaffee formation on 

south slope of Mount Zion 

Pink, slightly conglomeratic ql.lartzite _______________ _ 

Cross-bedded pink quartzite ________________ _ 

Massive white quartzite _____________ ..: ______ ~~~~~~~~ 

Conglomeratic very light pink quartzite. Grains are 

subangular and clear and composed of quartz only. 

Some irregular cross-bedding at base _______________ _ 

White very pure quartzite·--------------------~ 

Finely conglomeratic iayer, with subangular clear q~-a-rt~ 

grains ----------------------------------------- Greenish shale, very distinct ________________________ _ 

Poorly conso.lidated brown coarse sandstone ___________ _ 

Feet 

7 

1.5 

1.5 

7 

10 

2. 5 

1 

3 

33.5 

25 Emmons, S. F., Irving, J.D., and Loughlin, G. F., op . cit., pp. 31-32. 26 Kirk, Edwin, The Devoqian of Colorado: Am, Jour. Sci., 5th ser., vol. 22., pp~ 

231-239, 1931. . 

Section of Parting quartzite member in the Iowa Amphitheater 

Pinkish, "rotten" -weathering conglomeratic quartzite· 

irregularly cross-bedded; conglomerate layers len~ ticular ___ ____ __________________________________ _ 

Shaly, blocky limestone, in beds 3 inches thick _________ _ 

Pink massive quartzite _____________________________ _ 

Feet 

8.5 

2. 5 

8 

19 

Section of Parting quartzite member on east slope of West Dyer 

Mountain near Leadville 

Pinkish-weathering conglomeratic quartzite in beds as 

much as 2 feet thick; cross-bedded, especially at base __ 

DYER DOLOMITE MEMBER 

Feet 

21 

General features.-Overlying the Parting quartzite 

is the t Blue limestone of Emmons. In the LeadvilleAlma region this division is about 200 feet thick. In 

the report of Emmons, Irving, and Loughlin 27 the 

upper portion of the Lead ville was considered as being 

of Mississippian age, on the basis of paleontologic 

determinations by Girty. The lower portion was 

referred tentatively to the Devonian on the basis of 

probable correlations with known Devonian limestones 

in nearby areas~ as suggested by Girty .

28 in 1903, no 

fossils being known from it around Leadville. Behre 29 

~nd Kirk 30 have presented detailed evidence supporting these conclusions. 

The term "Leadville limestone" is used in this 

paper to include only that portion of the tBlue limestone of Emmons which is of Mississippian age. In 

accordance with Kirk's suggestion, the term "Dyer" 

is used for the Devonian portion of the t Blue limestone. 

The Dyer dolomite member consists of dense dolomitic limestone. The color is gray to bluish gray o~ 

.fresh surfaces. The upper beds generally wen,ther to a 

brownish tint, which may vary from a yellowish tan to 

, a deep brown. The lower beds locally show alterna-

. tions of light and dark materials. Thin shale partings 

occur along the surfaces of bedding _planes. . The . beds 

become somewhat shaly or :sandy toward the base. 

Locally they contain thin beds of ~?hale or sandstone. 

Thickness.-The thickness of th~ Dyer member 

· shows considerable variation. · In a few places it is 

more than 80 feet thick; in other places it is absent. 

In the vicinity of Leadville it averages about 75 feet 

and reaches a maximum of 95 feet, but around Alma it 

is thinner. This variation in thickness is probably 

more the result of pre-Leadville erosion than of great 

original differences in deposition. As Kirk 31 states: 

27 Emmons, S. F., Irving, J.D., Loughlin, G. F., op. cit., p. 37. 

~ Girty, G. H., The Carboniferous formations and faunas of Colorado: ·u.s. 

Geol. Survey Prof. Paper 16, p. 162, 1903. · · · 

29 Behre, C. H., Jr., Revision of structure and stratigraphy in the Mosquito Rartge · 

and the Leadville district, Colo.: Colorado Sci. Soc. Proc., vol. 12, ·pp. 37-57, 1929. 

3° Kirk, Edwin, The Devonian of Colorado: Am. Jour. Sci., 5th ·ser., vol. 22, 

pp, 231-239, 1931. 

31 Idem, pp. 226-227. 
PALEOZOIC FORMATIONS OF THE MOSQUITO RANGE, COLORADO 25 

It must be borne in mind .that the important erosional unconformity affecting the Leadville is the one within it, that is below 

the sandstone approximately 75 feet above the base of the 

limestone at Leadville and at the base of the Mississippian. 

The assumed unconformity of earlier geologists between the 

composite Leadville and Parting quartzite probably does not 

exist in fact and represents no more than an abrupt change in 

lithology. It is to be expected that if not at Leadville itself 

at least within a short distance to the north sections will be 

found where the Mississippian cuts through the Devonian 

limestone and rests on the Parting quartzite. An interesting 

section on Mount Zion (east) studied by Behre is suggestive of 

this condition. According to him (personal communication) 

the yellowish-weathering Devonian limestone is wholly or 

mostly absent. 

The variable thickness and general relations are 

shown -in the· table of formational thicknesses in the 

Alma district (p. 18 ). 

Age and correlation.-- Few fossils have been found 

in the Dyer in the Mosquito Range. Kirk 32 states: 

Paleontological evidence as to the age of the lower part of the 

Leadville at Leadville is poor. On West Dyer Mountain we 

collected several specimens of Syringopora sp. [which, by itself, 

is not conclusive. However,] apparently identical Syringopora 

was collected at Gilman, 20 miles away, below the Spirifer 

animasensis zone. 

The writer, in 1930, found similar Syringopora on 

the lower (northeast) end of Pennsylvania Mountain 

and again near Trout Creek. The Dyer member is 

considered the equivalent of at least the lower portion 

of the Ouray limestone of southwestern Colorado. 

DEVONIAN-MISSISSIPPIAN BOUNDARY 

On canyon walls and cliffs the Devonian-:Niississippian boundary can be clearly drawn in many places 

on the basis of color, as some beds near the top of the 

Devonian portion almost invariably assume a tan, 

"buckskin," or brownish coloration on weathering, 

whereas the Mississippian beds retain a dark gray or 

gray-blue color. Similarly it has been frequently 

noted that on old weathered surfaces the Mississippian 

beds tend to develop shallow caverns and solution 

features which were not observed on surfaces of the 

Devonian. 

Behre 33 has shown that in the Leadville district a 

siliceous bed marks the base of the Mississippian. 

This bed -occurs about 75 feet above the base of the 

tBlue limestone. It ranges from 2 to 12 feet in thickness and averages .about 8 feet. The sandy bed was 

noted locally in the Leadville district,34 but nothing 

definite could be stated regarding its continuity. 

It is now known to be of widespread occurrence, as it 

is not only persistent in : the Iowa Gulch district but is 

present on Zion Mountain, 4 miles north of Leadville, 

and at Gilman, 20 miles farther north. At these · 

32 Kirk, Edwin, op. cit., p. 226. 

33 Behre, C. H., Jr., op. cit., pp. 38-39. 

~4 V.S, GE)ol, Survey Prof. Paper l48, p. 34, 1927. 

places it is· 70 to 80 feet above the Parting quartzite. 

The typical sandstone is white, with a sugary texture 

and medium to coarse grain, but nowhere resembles a 

conglomerate. Its grains are held in a calcareous and 

siliceous matrix. In some places it approaches quartzite in character, and in others it is little more than a 

limestone with numerous quartz grains. In parts of 

the Leadville district it seems to be represented by 

shaly instead of sandy layers, a fact which may account 

for its previous inadequate recognition., Immediately 

above this sandstone there is generally a conspicuous 

limestone breccia from 2 to 5 feet thick, composed of 

va,riovs colored fragments of limestone set in a sandy 

calcareous matrix: Gibson 35 found the same sandstone and breccia in the Red Cliff district. 

The widespread oceurrence of this sandstone 4~s 

also been confirmed by the detailed observations of 

E. P. Chapman, of Leadville. It seems to represent 

the beginning of Mississippian sedimentation and ·is 

inch1ded in the Leadville formation in this paper. 

The sections given below jilustrate the character of 

the Leadville and Chaffee formations in the Leadville 

district. 

Composite section on south s'lope of Mount Zion, near Leadville 

[Supplied by C. H. Behre, Jr. 

W:hite porphyry sill. 

Leadville limestone: Feet 

Altered, coarsely crystalline Blue limestone. Light 

blue-gray; local black chert lenses. Weathers to 

"checkered" color pattern that brings out dark 

splotches__ __ _____________ ___________________ 20 

'Similar to above, but beds not coarsely crystalline_ 40 

Similar to second above but free from chert-_-_---- 23 

Dense cherty dark blue-gray layers (secondarily 

silicified?) ___________ - - - - - - - - - - - - - - - - -·- - - - - - - 57~ 

Blue-gray limestone, much like the last but locally 

recrystallized into "zebra" rock_______________ 14 

Blue limestone, with black chert lenses and spheres 

and local shaly layers ______________ ,___ ________ 37% 

Conglomerate of limestone boulders and pebbles in 

a lime matrix. Individual boulders not well 

rounded. - Some black chert pebbles also. In 

middle 1 foot of coarse yellowish-weathering 

arkosic sandstone, cemented with lime_________ 5 

Total thickness of Leadville formation________ 145 

Dyer dolomite member of Chaffee formation: 

Limestone in beds generally as much as 3 feet thick 

but be1

dding not well marked. Banding locally 

visible, the banding due -to alternations of light 

and dark gray colors_________________________ 24Jh 

Similar to above _ but _ beds thinner-few more than 

1 foot thick. Many are shaly, with distinctly 

granular weathering. Largely individual lime 

beds are separated by layers 1 to 4 inches thick of 

brick-red or greenish shale____________________ 10 

Yellow thin-bedded, very shaly limestone, with 

irregular cross-bedding __ __________ ____ -_------ 8 

35 Gibson, Russell, in Crawford, R. D., Geology and ore deposits of the Red Cliff 

district, Colo.: Colorado Geol. Survey Bull. 30, pp. 361 381 1925, 
26 SHORTER CONTRffiUTION'S TO GENERAL GEOLOGY, 1934-35 

Composite -section on south slope of Mount Zion, near Leadville-

. Continued 

Dyer dolomite member of Chaffee formation-Contd. 

Shattered, irregularly bedded, sljghtly sandy layer 

Pinkish limestone, in beds6 inches thick _________ _ 

Shattered concretionary layer; conspicuously brownish __________________________________ _ 

Light-gray, uniformly white-weathering limestone; beds blocky, 1 foot. thick _____________________ _ 

Total thickness of Dyer dolomite member ____ _ 

Feet 

1% 

8 

2 

41% 

95% 

Detailed section on Sherman Mountain, Iowa Amphitheater, 

near Leadville 

[Supplied by C. H. Behre, Jr.] 

Leadville limestone: Feet 

Blue-gray, granular, shattered limestone__________ 16~ 

Alternate blue·-gray and buff-weathering limestone, 

in beds 1 to 2 feet thick______________________ 10~ 

Dark blue.,.gray limestone, with so~e rusty-weathering cherty bands_____________________________ 8772 

Limestone breccia______________________________ 6 

Buff-weathering sandy beds_____________________ 6 

Total thickness of Leadville limestone________ 126% 

Dyer dolomite member of Chaffee formation: 

Light-gray, pinkish-weathering quartzite and thin limy beds, alternating _______________________ _ 

Alternate light and dark banded shaly limestone, the banding 6 inches thick ___________________ _ 

Same as above but weathering brownish to buff ___ _ 

Dark blue-gray limestone, weathering bright buff __ 

Blue-gray streaked limestone, in beds 1 to 2 feet 

thick, with some siliceous banding. Beds lower 

down become massive, as much as 3 feet thick, and weather rusty __________________________ _ 

Total thickness of Dyer dolomite member ____ _ 

Detailed section on West Dyer Mountain, near Leadville 

28~ 

4 

10% 

39 

87~ 

Leadville limestone: Feet 

"Pepper and salt" dark-gray beds of coarsely crystalline limestone, partly "zebra" -marked_______ 20 ± 

Dense, highly recrystallized blue-gray limestone, 

weathering to dull dark gray. Fracture brittle___ 2 

"Pepper and salt" dark-gray beds of coarsely crystalline limestone, partly "zebra" -marked_______ 11 

Dense, closely fracturing sandy limestone, with 

closely banded fetid beds near the middle. Color 

deep slate-gray . where fresh; weathers buff; the 

bands are accentuated by weathering.,__________ 33 

Dull blue-gray limestone; weathers buff. Delicate 

recrystallization outlines fossil traces in white. 

Rare chert lenses as much as 2 inches thick, 

locally in definite beds. Some darker blotching__ 20± 

Typical "zebra" rock, dull dark gray, almost black 

limestone, locally spotted or blotched wrth darker 

color. Areas of recrystallization and "zebra" effects common _____________________________ ·13± 

Dense slate-colored (blue-gray) limestone. Shows 

faint banding on the weathered surface, which is 

dark gray, slightly lighter than when the rock is 

fresh. Suggestions of wormholelike markings, 

elongated parallel to the beds. Lower part contains rare bands of iron-stained chert___________ 22 

Detailed section on West Dyer Mountain, near Leadville-~Contd. 

Leadville limestone-Continued. Fert 

Light-colored, moderately fine textured lim~!>!tdtH~, 

with traces of limestone breccia locally nefir base~_ 14 i: 

Slightly sandy, very brittle light-gray limestone, 

· weathering a slightly darker shade~_~ __ ~~~~~~~~ S dt 

Limestone breccia; subangular fragmehts or lim~-

stone, from very light slate-gray to almOE3t tloa1-

black, set in sandy buff lh:ne~tdne as matrix______ 8 

Very sandy limei'$t!Jne, with quartz grains weathering 

out of expdsed ~lirface ;light buff __________ --___ 3 

Total thickness of Leadville limestone ____ ------ __ 154 

Chaffee formation: 

Dyer dolomite member: 

Dense, blue-gray limestone in massive beds. 

Color slaty blue-gray, weathering to light 

buff-gray. Faint suggestion of banding_- __ 

Brownish spotted gray limestonli), densely granular, thin-bedded; weathers so as ·to show 

distinct bands 1 to 2 inches thick ____ - ____ _ 

Like the beds above, but less distinctly banded_ 

Light blue-gray limestone with pronounced 

platy fracture; weathers to an ocher color, 

14 

8 

29± 

very conspicuous________________________ 4 

Massive light blue-gray, faintly bu~-weathering limestone. Massive beds; becomes whiter 

near base ____________________ - - - - - - - - - - - 30 ± 

Very sandy, medium fine to locally coarsely 

crystalline limes~one of light-buff color_____ 14 ± 

Total thickness of Dyer dolomite member__ 99 

Parting quartzite member: Pinkish, coarsely granular quartzite; .locally conglomeratic. 

Total thickness measured ______ - ___ --__ 253 

Section on east slope of West Dyer Mountain near Leadville 

[Supplied by C. H. Behre, Jr.] 

Leadville limestone (partly eroded at top): Feet 

Dark blue-gray limestone, with beds prominently 

weathering to rusty brown; cherty, especially in 

lower part, the chert in black lenses _________ --_ 23 

Alternating very dark and very light blue-gray limestone, with black chert nodules ____ ------------ 27 

Buff sandy limestone ____________________ ------- · 2 

Light-gray matrix studded with dark and light gray 

poorly rounded blocks of limestone--limestone conglomerate ____________________________ - _ _ 8 

Total thickness of Leadville limestone________ 60 

Dyer dolomite member of Chaffee formation: 

Banded dark blue-gray and light blue-gray limestone_______________________________________ 10 

Buff-weathering, light-gray massive limestone_____ 27 

Gray limestone, slightly bluish, in irregular massive 

beds 2 feet or less thick; black chert lenses near the 

top_________________________________________ 21 

Blue-gray limestone; weathers to dull, dark-gray___ 10 

Buff-weathering massive beds of limestone, with 

limestone conglomerate at base________________ 10 

Total thickness Qf Dye:J;" cl<>lomtte memb.e:r- ~ ~ _ _ 78 
PALEOZOIC FORMATIONS O,F THE MOSQUITO_ RANGE, COLOR_ADO _-27 

CARBONIFEROUS SYSTEM 

LEADVILLE LIMESTONE (MISSISSIPPIAN) 

General features.-The Leadville or upper part of 

the t Blue limestone overlies the Dyer dolomite member of the Chaffee formation and is the formation ·in 

which the largest ore boclies in the region have been 

mined. As shown in the sections, it consists of dense 

blue to blue-gray dolomite, some layers of which contain numerous lenses, concretions, and streaks of 

black chert. Locally metamorphism has given rise to 

banded patches of -white recrystallized dolomite to 

which the miners have applied the ntlbme "zebra. rock." 

In the northern part ?f the range eont~9t. me~p.m~rphism has eaused considerable local al te.ra twns of the 

formation, which change its appearance and give it 

different characteristics of weathering. The features 

by which it may be distinguished from the underlying Dyer member of the C4affee have been treated. in 

the discussion of that formation. 

West and southwest of the area of the Mosquito 

Range the Leadville formation gradually loses its 

dolomitic character, becoming a pure limestone. This 

is very noticeable as it ir; followed south from the 

Eagle River to the Aspen mining district. 

Thickness.-The thicknesses measured range from 

less than 50 feet to 160 feet. The thickness changes 

~arkedly within short distances, and the differences -

appear to have resulted more from erosion preceding 

the deposition of the Pennsylvanian sediments than 

from original differences in deposition. 35a 

Age ani correlation.-Fossils are rare in the Leadville formation. _None were found by the writer during his field work in this area. In fact, practically 

ail the known fossils from the formation in the Mosquito Range area were obtained in the early days by 

Emmons and his assistants. The fossils reported are 

Zaphrentis sp., Orthotetes inaequalis, Spirifer sp. a 

Girty, Spirifer sp. b Girty, Seminula subquadrata, 

Eumettia woosteri, Myalina arkansana?, Oonocardium 

sp.?, and Straparollus cf. S. spergenensis. Girty 36 

expresses the opinion that the fauna is equivalent to 

the Kinderhook and possibly lower Burlington of the 

Mississippi Valley. He also considered it to be more 

closely related to the Millsap limestone of the Front 

Range than to the Mississippian limestones of Aspen 

and Crested Butte. However, all form a general 

equivalent of the Madison limestone, so widely deposited over the Northern · Rocky Mountain province. 

MISSISSIPPIAN -PENNSYLVANIA~ BOUNDARY 

Though there is no apparent discordance in dip 

between the Mississippian and Pennsylvanian in the 

regions here studied there is an unconformity between 

them which represents a time interval of great length36& Lovering, T. S., and Johnson, J. H., Am. Assoc. Petroleum Geologists Bull., 

vol. 17, pp. 366-367, 1933. 

36 Girty, G. H., The Carboniferous formations and faunas of Colorado: U.S.Geol. 

Survey Prot. Paper 16, pp. 217, 2~W, 1!)(13. 

equal, in fact, to about half of the Mississ~ppian and 

part of the early Pennsylvanian. _This is evident 

from the faunas. The lithologie change from limestone 

to shale is abrupt, with a slight suggestion of ,sand or . 

gravel at the contact in a few places. Signs of weathering and solution were noted in the upper layers of the 

limestone - in several - localities, A short ·distance 

northwest of the area here discussed, in the ,Red Oliff 

and Gilman districts, signs of weathering _and ~ro~ion, 

with solution of the upper Leadville before deposition 

of tb,e overlying Weber (?) formation, -are _ ~vide;nt. 

In fact; in the mines at Gilman the contact is uneven, 

and the funnel-shaped masses of the younger fo;rll).ation penetrate into the limestone, suggesting fillings 

of old sink holes and solution cav-rities.37 The surlttce 

outcrops in the same: vicinity show that th,e younger 

formation rests on ftll irregularly eroded surface of 

limestone. Similar occurrences of Pennsylvanian ~hale 

resting on irregularly eroded limestone surff\ces w~re 

also ~bserved during 1931 at several localities ·in the 

Aspen dist"rict and along the west side .of • the Holy 

Cross uplift. 

PENNSYLVANIAN AND PERMIAN SEDIMENTS · 

GENERAL FEATURES 

Above the Leadville lime~ tone rises a series .of ~~~le, sandy shale, limestone, sandstone, and gr~ts, wlp.,ch 

ranges upward without stratigraphic . 'break into fed 

beds of great thickness. Emmons _ n _.the ~eadvi)le 

mo~ograph applied the terms _ t'l~eber sh~les/' a:nd 

t"Weber grits" to the low~r part .Qf' the ~~r~es, ,·on the 

supposition that it was equiv'alent to t~e Web~r 

quartzite of northern Utah. For-the upperpo:rtion of 

the series, which consisted mainly of red b~ds, h~ used 

the tern1 t" Upper Coal Measures" and lat¢r88 the term 

"Maroon formation", considering them to be e(plivalent to the formation that constitutes Maroon· Pe-ak 

southwest of Aspen. In the Tenmile dis~rict_ he_ fou~d 

still higher beds, to ,which he applied the ter~ t"~yoming formation," a term first us~d for deposits to_ the 

east of the Front Range. _ ·_ - . ·. . _. . 

Lacking paleontologic evidence and withou,'t disti:?-ctive lithologic features to aid him, he arbitra~ily . sep~

rated the formations at certain linie.stone "9eds that were 

-well developed in the Tenmile-district. Thus. the,base 

of the Maroon was considered to be the base of a l.inlestone to which he applied the name "Robinson," and 

the top member of the· formati9J?- was his Jacql_le 

Mountain limestone. There seems tQ be no . neeq or 

justification for separating the sedirp.ents ~hove t~e 

Jacque Mountain limestone from those below_, so In 

this report the term "Maroon formation'~ is used 'to 

include both. The term t"Wyoming" ha~ b~~n 

abandoned. 

Very little of the Maroon Jormati?n is-left iri ~he 

Leadville dis~rict, and in general it is not well exposed 

37 Barcherdt, W. 0., Eng. and Min. Jour., vol. 132, p. 100, 1931. 

38 U.S.Geol. Survey Geol. Atlas, Tenmile district special folio (no. 48), 1898. 

• 
• 

SHORTER CONTRIBUTIONS TO GENERAL GEOi.OGY 1 l \Ja4-"-S5 

il\ the Mosquito Range. It is, however, well developed 

ip -the region north and northwest of Leadville, and 

most of the information used in this discussion was 

r&btained in that area. 

WEBER (1) FORMATION (PENNSYLVANIAN} 

Subdivisions.-Three general zones can be roughly 

recognized in the Pennsylvanian sediments of the 

M,osquito Range-a lower shale zone, a limestone zone, 

and· the upper zone of grit. These zones grade into 

~ne another and are not everywhere well defined. 

The lower zone averages about 300 feet in thickness 

and consists mainly of dark shale, though locally thin · 

sand and even shaly limestone may occur. In the 

Leadville district the individual layers are usually less 

than a sixteenth of an inch thick. They contain much · 

c~rbonaceous material, locally even thin beds of impure 

coal. At two localities well-preserved land plants 

were obtained, but traces of vegetable matter were 

moted at this horizon in all the sections studied; Along 

{Trout Creek numerous pieces of silicified wood, some 

::of the:q1 large, were obtained. In some sections part 

of the :shale is calcareous. Suggestions of a sandy or 

slightly conglomeratic basal layer were noted at a few 

localities, but generally very fine shale was deposited 

immeditely upon the surface of the Leadville limestone. 

Throughout the series interbedded layers of coarse 

micaceous sandstone occur. These are more abundant and ·thicker at the north end of the Mosquito 

Range than at the south end. The contact between 

the upper and middle zones n1ay be well defined in a 

-few sections, but more commonly there is a gradual 

'.f.transition. This zone corresponds to the t Weber 

· ~hale~ of Emmons. 

·-; · The middle zone, which is 700 to 1,000 feet thick, 

consists of grit, sandstone, sandy shale, shale, and 

limestone, named in the order of their abundance. The 

limestone is dolomitic and contains some iron carbonate. Many of the limestone beds carry marine fossils. 

The limestone beds constitute only 3 to 8 percent of 

the deposits, yet from their resistance to weathering 

and from their coloration they form the conspicuous 

outcrops. Nearly all the thicker limestone beds of the 

local Pennsylvanian occur in this zone. The shale of 

this zone is not so carbonaceous as that in the lower 

·.zone. Many of the beds are calcareous. Locally they 

may be micaceous. The sandstone is white to light 

gray. The beds are commonly micaceous, the number 

and size of the mica flakes increasing progressively 

at higher stratigraphic levels. This zone is approximately equivalent to the t Weber grits of Emmons. 

The upper zone consists mainly of coarse-grained 

sandstone and grit, which locally become coarse conglomerates. In general the texture becomes coarser 

toward the top of this section. Thick, irregular beds 

of coarse grit and conglomerate are characteristic of 

this zone, alt-4ough it contains local beds of sandy 

shale and tt f~w l~nti~ular beds of limestone. Its thickhe~s difl)3ts greatly from place to place but reaches 

1,200 to 1,800 feet at the north end of the area and in 

th~ Tenmile district. Much of the material is arkose. 

Feldspar fragments may be so abundant as to aid in 

coloring the rock. Mica is surprisingly abundant in 

many of the beds. In some beds it is scattered 

through the rock; in others it occurs !fiainly on and 

near the bedding planes. The coarser conglomerates 

contain fragments of pre-Cambrian granite and schist. 

In general the deposits are such as one would expect 

to result from rapid deposition as wash, alluvial fans, 

and deltas ai;<;mnd areas of pre-Cambrian rock. Most 

of thi~ zone belongs with the Maroon of Emmons. No 

lithologic boundary can be drawn between the "Weber" 

and Maroon. 

Age.-The typical material of the so-called ''Weber'' 

in. the region where it was originally studied (the 

Leadville district) is unquestionably of Pennsylvanian 

age, as can be demonstrated from the abundant fossils 

collected at a large number of localities. Full faunal 

lists and a statement regarding their interpretation are 

given on pages 31-33. 

Relation to ore-bearing beds.-The so-called "Weber" 

formation has been of interest to the mining men 

because experience has shown that it is stratigraphically above the top of most of the ore beds of the 

Leadville and Alma districts. Numerous efforts have 

been made to locate ore within this formation, but it 

. has been productive only in the Robinson and Kokomo 

districts. The lower shale member appears to have 

served as an impervious blanket that stopped the 

upward migration of ore-bearing solutions and thereby 

caused an increased concentration in the underlying 

Mississippian limestone in a number of places. 

Lithology.-The Pennsylvanian sediments include 

such a variety of types that it seems desirable to give 

them special study. 

The shale beds include purely argillaceous material, 

calcareous shale, bituminous shale, and sandy shale. 

They are best developed at and near the base of the 

formation. Over 85 percent of the shale observed 

was contained in the lower 450 feet of the Pennsylvanian. (See pl. 3, B.) 

Generally the shales are black or dark gray, but 

they may be light gray, tan, brown, or red. The 

basal shales are universally black; the red and redbrown colors occur highest in the section. 

Biturninous shale is common at the base of the formation. Around Leadville there is 50 to 70 feet of it. 

Usually it is purer and of finer texture near the base. 

The carbonaceous matter is largely if not entirely of 

vegetable origin. Plant fragments, root impressions, 

carbonized wood, coaly material, and even streaks of 

impure coal occur. At two localities well-preserved 

fossil ferns and related land plants were obtained. In 

the Trout Creek section w~ll-:pres.e:rved silicified woo~ 
U.S. GEOLOGICAL SURVEY PROFES

A. tWEBER GRITS ON SOUTH MOSQUITO CREEK. B. tWEBER SHALES ON LONDON MO

C. MANITOU LIMESTONE WITH CHERT. D. SAMPLE OF t WEBER GRIT
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 185 PLATE 4 

c 

ROCKS OF WEBER U) FORMATION. 

A, Micaceous sandstone. B, Ripple-marked sandstone. C, Micaceous sandy shale. D, Micaceous arkose. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 185 PLATE 5 

B 

TOP AND SIDE VIEWS OF A THIN LAYER OF FIBROUS LIMESTONE FROM THE LOWER PART OF THE MIDDLE WEBER (il) BEDS. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 185 PLATE _6 

A. CASTS OF SALT CRYSTALS ON SURFACE OF SHALY LIMESTONE FROM LOWER PART OF WEBER(~) FORMATION NEAR_TROUTCREEK. 

B. ARKOSIC GRIT FROM UPPER PART. OF WEBER (?) FORMA.TION IN ALMA DIST~ICT. 
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 185 PLATE 7 

A. OUTCROP OF FREMONT, HARDING, AND PART OF MANITOU ALONG TROUT CREEK NEAR OLD NEWETT STATION. 

R. LOG OF SILICIFIED WOOD FROM THE LOWER PENNSYLVANIAN NEAR TROUT CREEK. 
PAIJEOZOIC FORMATIONS OF THE :MOSQUITO RANGE, COLORADO 29 

was abundant in the upper part of a thick shale b~d. 

Some shale beds are so carbonaceous that they have 

been prospected for- coal, but as yet no commercial 

coal has been found. 

Beds of dark-gray to black calcareous shale were 

noted in the lower zone of the Weber (?) formation, 

usually above the highly bituminous shale, and in the 

middle zone associated with the limestone. Most of 

those noted were not fossiliferous, but in a few locali-· 

ties-for example, on the south side of Empire B:ill 

and on the hill northeast of Levick-many marine 

invertebrates were obtained. In the Trout Creek 

sections both brackish-water and marine invertebrates 

were found in some of the shales. .,_ 

Sandy shale is most common in the upper part of 

the lower zone and in the middle zone of the formation. 

The beds are black, dark gray, light gray, tan, brown, 

red-brown, and red. In character they range from 

nearly pure shale to sandstone. The texture is usually finest in the lower beds and becomes coarser higher 

in the section, but this is not universal, as there nre 

many and locally abrupt changes in lithology. Many 

of the sandy shale beds are micaceous, especially in 

the middle zone, the ·mica flakes being generally 

small but locally surprisingly abundant. (See pl. 4, 

0.) Certain beds of black sandy shale near Aim~ :~re 

so micaceous that in hand specimens of fresh material 

they might easily be mistaken for mica schist. . 

Limestone may occur throughout the formation 

(see pls. 5, A, B; 6, A, B), but it is most common in the 

middle zone. The thickness of the beds ranges from 

less than 1 inch to 50 feet, but most beds are less 

than 10 feet thick. Where fresh the color is dark 

gray to black, but many beds on weathering take on a 

brownish tint, becoming a rich chocolate-brown. 

Usually the limestone is rather massively bedded and 

has a distinctly crystalline texture. Analyses ~how it 

to be dolomitic and commonly somewhat ferrugi:Qous. 

Most of the limestone beds contain fragments of 

marine organisms. in a few beds good fossils :are 

abundant, but the crystallization of the limestone has 

spoiled many of the fossils and made them difficult to 

obtain from unweathered r'ock. 

Though some beds of limestone were traced for 

miles along the outcrop, the individual beds tend to be 

lenticular and discontinuous. Calcareous deposition 

was widespread at some horizons, however, for l~Inestone and calcareous shale occur at about the same 

stratigraphic levels, though the individual beds do not 

carry through. 

In the sections actually measured the limestone 

beds form 3 to 8 percent of the total thickness of the 

sediments. 

Sandstone is the most common rock of the Pennsylvanian deposits. (See pl. 4, B.) Together with the 

grit and conglomerate it makes up 83 percent of the 

sediments in the sections measured. The color is 

tH~ua.lly a light gra.y, but white, dark gray, black, pink, 

tan; brown, and red were also noted. Many of the 

beds in the lower part of the section are intensely 

black, · owing to some carbonaceous, apparently 

bituminous substance in . the cementing n1aterial. 

Certain specimens are composed largely of coarse 

grains of white quartz in a black cement that has the 

color and luster of liquid shoe polish. Emmons 39 

remarks concerning these black sandstones: 

The sandstones often contain so large a quantity of carbonaceous material as to become quite black. This carbonaceous 

material, which is insoluble in ether, alcohol, or sulphide of 

carbon, is probably either graphite or anthracite. 

The belief that the gray and black coloration is due 

to carbonaceous material is fvrther strengthened by 

the fact that in the contact areas around the larger . 

intrusions the sandstone beds are commonly white, 

whereas the same beds where not affected .by the 

intrusions· are dark. This change can be well seen in 

the amphitheater above the London mine, northwest 

of Pennsylvania Mountain. Here fine-grained sandstone beds in the lower part of the Weber (?) forn1ation 

have been altered to white quartzite. ··, 

In most of the sections studied the sandstone 

beds become coars~r irt texture at progressively higher 

stratigraphic levels. They also tend to become ·progressively more arkosic, and the upper part contains 

many thick layers of arkosic grit or conglomerate. 

This grit is composed of pieces of quartz, feldspar, 

some mica, ·and more rarely gneiss, schist, or granite 

(pls. 3, A, D; 6, B). Fragments of sandstone, shale; 

and limestone were noted in a few specimens. -The 

constituent fragments may be well rounded and 

smooth, but in many specimens the rounding is not 

complete. Feldspar may be present in such amounts 

as to give a pink tint tb the rock. Mica is noticeable 

in most of the bed.s of sandstone and grits and is surprisingly abundant in some of .them (pl. 4, A, D)-in 

fact, so abundant that Emmons 40 doubted that it 

could have been derived from the older rocks. Observations of the pre-Cambrian rocks of the district, however, 

show that they could easily have supplied the mica, for 

many of the larger piebes contain inclusions of hematite identical with .those observed in the mica. of the 

pre-Campria.n gra~te, and a microscopic study of the 

mica in the sand§tone and shale shows that it was 

deposited a.s a part of the original sediment. The 

miea flctkes are torh, frayed, scratched, crinkled, and 

show other evidences of wear. 

The individual beds of grit may locally attain thicknesses of 40 or 50 feet but are decidedly lenticular. In 

many places they. have well-developed cross-bedding. 

The following descriptions of the samples collected 

from the Windy Ridge section is given to show in 

39 Emmons, S. F ., Geolo~y and mining industry of Leadville, Colo.: U.S.Geol. 

Survey Mon. 12, p. 68, 1886. 

• 0 Emmons, S. F ., U.s.d€ol. Survey Geol. Atlas, Tenmile district special folio 

(no. 48), p. 1, 1898. 
30 SHORTER. CONTRIBUTIONS TO GENERAL GEOLOGY, 1934-35 . 

detail the character of the sandstone and associated 

rocks. This is a typical section of the upper zone of the 

Weber (?) strata. 

Samples collected· from the upper part of the Weber (?) formation 

on Windy Ridge, north of Alma 

[See Windy Ridge section, p. 37] 

Black conglomeratic quartzite; grains chiefly quartz and 

feldspar, well rounded, 0.8 to 11 mm; quartz grains mostly gray 

with pronounced greasy luster, few white or transparent, 

·colorless; feldspar grains white to creamy white with good 

cleavage and slight alteration to kaolin; a small amount of 

muscovite in flakes 0.8 mm across. 

J-23. Dark-gray shaly micaceous quartzi~e ; resembles.~gpartzmica schist; quartz grains angular and subrountl, 9.30 fum 

maximum; muscovite relatively abundant, in decidedly crinkled plates 20 mm across; A little biotite. 

J-24. Gray micaceous sandstone. Quartzitic. Distinctly 

laminated. Sand grains angular, 9.15 mm. Muscovite abundant. Biotite present in small amounts. The rock has metamorphic characteristics, with the app~arance of a phyllite. 

Mica grains are 0.40 mm in diameter. The specimen is greenish 

when wet. 

J-25. Gray quartziti~ . conglomerate. Large grains well 

rounded. Grains variable in size, 20.0 mm maximum diameter. 

Largest grain consists of shaly sand or quartzite similar to J-30 

and J-49-S. A few of the grains are of attached quartz and 

feldspar, probably granite pebbles. Muscovite present in 

small amounts. 

J-25-40. Micaceous quartzite sandstone. Dull, dark-lavender color. Quartz grains angular to subround, 0.3q min maximum diameter. Muscovite very abundant. Some flakes-5.0 

mm across. The flakes are decidedly crinkled and contain 

hematite inclusions. 

. J-26. Micaceous quartzite sandstone. Looks like quartzmica schist or phyllite. Variable grain size, 0.30 mm maximum, 

a11gular to subround. 

J-28. This specimen is similar to J-31 except that some of 

quartz grains are as much as 2.0 mm in diameter. 

J-29. Gray dolomite. Massive, fine-textured, even-grained. 

Diameter of grain on cleavage faces ·averages 0.29 mm. Irregularly fractured. Thin layers of calcite along fractures: 

J-30. Gray · shaly micaceous quartzite. Quartz grains 

angular and subround, 0.30 mm maximum. Muscovite relatively abundant. Material poorly laminated. The shale 

layers are fine-textured and crinkled. Muscovite flakes are 

also crinkled. Somewhat green when . wet. Looks like mica 

schist. 

J-31. Dark-gray micaceous sandstone. Massive, nearly 

quartzite. Fine, uniform grains. The quartz grains are angu-. 

lar to subround, 0.30 mm average diameter but range from 

0.11 to 0.60 mm. The muscovite flakes are as much as 12 

mm in diameter, and many show hematite inclusions. The 

largest flakes occur along the indistinct bedding planes and 

along fractures. The specimen has the appearance of a mica 

schist. 

J-32. Gray micaceous shaly sandstone. Very quartzitic, 

distinctly laminated. Sand grains angular, 0.15 mm average 

diameter. Muscovite abundant. Biotite present in · small 

amounts. The mica .grains ani 0.40 mm in diameter. Color 

greenish when wet. The rock has the appearance of a phyllite. 

· J-34. Gray sandy shale. Alternating light and dark-gray 

bands. Light bands are sandy, but sand grains are very 

fine, O.Of) mm average diameter. The rock is well laminated 

and breaks along the least sandy streaks. Light streaks 

slightly calcareous. The rock has been altered and appears 

like a schist. 

,J-35. Gray quartzite. Massive. Grains of variable size, 

angular to round, 2.0 mm maximum diameter. Minerals are 

essentially quartz, feldspar, and muscovite. The quartz is 

gray and has a very greasy luster. The feldspar shows some 

alteration. 

The Pennsylvanian sediments have all been definitely consolidated and lithified since they were deposited. The · shale is well compacted, the limestone is 

crystalline, and the sandstone and grit are thoroughly 

ceill:ented. In fact, where encountered in fresh out-

·crops· and in rnine workings the limestone, sandstone, 

and grit are decidedly hard rocks. 

In the vicinity of Tertiary intrusive rocks metamorphism has aided in altering and hardening the sedi-

·ments. The shale has become slate and the sandstone 

quartzite. Color changes have also resulted. 

Sandstone, grit, shale, and limestone in meas_ured sections of Pennsylvanian sediments 

[None of the sections measured' reach to the top of the formation) · 

London Pennsylvania Empire Hill Board of 

I 

Evans Peak Horseshoe Trout Creek I Windy 

[· Mountain Mmmtain Trade (Upper) Ridge 

Per- Per- Feet cent Feet cent Filet 

----------

Sandstone ____________________ 1, 173 64 488 51 578 Shale ________________________ 143 8 147 16 231 Conglomerate and grits ________ 416 23 277 29 693 Limestone ____________________ 84 5 

1, 816 100 ~~-4~ 950 100 1, 560 

Paleontology.-The fossils obtained from the 

Weber (?) formation include plants and animals. 

The plant fossils are algae aud land plants. The algae 

are considered to be brackish-water and fresh-water 

forms, and the commonest type makes small glassy 

I 

Per- Per- Feet Per- Feet Per- Feet Per- Feet Per- cent Feet cent cent cent cent cent 

---------------------------

36 341 38 260 30 121 34 205 11 49 15 

15 361 41 99 11 103 30 1, 513 81 6 1 

45 41 5 490 56 98 28 0 0 258 78 

4 143 16 23 3 30 8 147 8 18 5 ----------

100 j352 ------- 100 886 100 872 100 1,865 100 331 99 

rods and tubes. The land plants collected were 

examined by Read, who has described the speciesY 

The species found at the several localities are as follows: 

41 Read, C. B., A flora of Pottsville age from the Mosquito Range, Colo.: U.S.Geol. 

Survey Prof. Paper 185-D, 1934. 
PALEOZOIC FORMATIONS OF THE MOSQUITO RANGE, COLORADO 31 

§gstJ (J-'=96 of Mf, Jdhhsoti1

s Peftnsylv11nia. Mountain 8ection): 

§Hgtiuuia veffucEJsit • 

N etifopteris di uho§ciiL 

Sphenopteris aspietiioides: 

eordaites sp: 

'fhis coiiectidrt fiiust be regarded as representing a middle ·.t'ottsviiie flora, as indicated by iiie Neu:fd'}Jteris, 

8049 and 8683 (J-42 arttl J-48 of Mf. Johnsdn;s Evans Peak 

section): 

Lepidostrobus weberensis. 

Stigmaria verrucosa. 

Calamites sp. 

Asterophyllites longifolius? 

N europteris dluhoschi. 

N europteris h~terophy lla. 

N europteris cf-N. gig an tea. 

Sphenopteris cf. S. microcarpa. 

Sphenopteris chea-thami. 

Diplotmema patentissima. 

Adiantites roc~yillontanus. 

Cordaites sp. 

Cordaianthus sp. 

Cordaicarpon sp. 

II 1 ty 

Trichopitys whitei. 

Dactylophylluln johnsoni. 

The plants here listed were collected at a horizon somewhat" 

higher than that of the plants in the first list. The developfi1ent of Neuropteris and Sphenopteris suggests a middle Pottsville age. 

Besides the forms identified, a large amount of wellpreserved silicified wood was obtained along Trout 

Creek! (See pl. 7, B.) 

The animal fossjls are listed in the table below. 

These include only forms collected during the present 

work. A few ot:ijer forms have been reported,, by 

earlier geologists bqt are not included, as there is so~e 

douo't as to the locality, horizon, or identification. ·The 

fossils listed in .the table were identified by the writer 

and checked by G~orge H. Girty, of the United States 

Geological Survey. Only crinoid stems, Chonetes 

geinitzianus, Margi;nifera ingrata, Productus cora, and 

Productus coloradotfl;sis were common. . Of the other 

species 26 are new. 

Distribution by locality of fossils obtained from the Weber (1) formation 

6851c 6851e 6~52 6852a 6853 6854 6855 685Sa 6f§t!_ 6857 6858 6860 6860b 6860c 6860d 6860e 6860f 

---·---------------1---------------------------------f--

OORA~S 

t:J)b~~h~li~~~~~~~~du~~~::::::::::::::: ==== ==== ==== ==== ==== -~- ==== ·x·- ==== :::: ==== ==== ==== ==== ==== ==== ====. Lophophyllum profundum var. sauridens ____________ X ________________ ---·- ________ X ---------------- _ _: __ ---- Lophophyllum sp.? .. ·.---------------------- ____________________ X ____________________ ------------------------

ECIUNODERMS 

Archaeocidaris sp. ?_ ___________________________ ~ _ _ _ _ _ _ X _ _ _ _ _ _ _ _ X __ .. _ _ _ _ _ X ____ ---- ---- ---- ---- ---- ---- Archaeocidaris era tis _____________________ . ___________ _ ...: X ______________ .. ____ ~ ______ -- ---- ---- ---- ---- ---- ---- Crinoid stems_ - __ - .,. ______________________ - _ _ _ _ _ _ _ X X X X X X - --- X - - -- ---- X X -- - - - - - - - --- Echinocrinus sp.? __ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X __________ .. __________ --- ---- ---- ---- ---- ---- ----

BRYOZ<U.NS 

Fenestella sp.? ____________________________ ---- ________ X ____________ ---·- ---- -------- ---- ---- ---- --.-- ---- --·-- Fistulipora sp.? ___________________________________________________ X ---- ---- ---- ---- ---- ---- ---- ---- -~-- ---- Polypora sp.? ____________________________________________ X _______ · _________________ ---------------- X ----

:e~~~:o~~o:;. ~~:~~~~~~~~~i-~e~~:: : :::: :: : : :: :: : : :::: :::: ~ :: :: : : :: :: :: :: ::: : : : = :: :: :: :: :: : : :: : : _ ~ _ :: : : :: :: : : :: 

Stenopora sp.? _________ ... _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X ______________ .. ___ ., ___ - _ ---- ---- ---- ---- ---- ---- ----

BRACHIOPODS 

Chonetes geinitzianus? _____________ , ________ ---- ____ X X ________ ---- X X ------------------------ ---!. ----

Chonetes aff. C. geinitf;ianus _______________________________________ X _____ ---.., ---------------------------- --~-

Chonetes sp.? _____________________________________________ X _____________ ---- .:. ___ ---- ---- ---- ---- ---- ---- ---- Cleiothyridina pecosL _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X __________________ .. __ '- ____ - _ -- -- -- - - --- - - - -- - - - - - -- - - - - - Cleiothyridina pecosi?_ ____________________ ---- ________________________ X ---~ -------------------------------- Cleiothyridina pecosi vat_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X __ - _ ---- - - - - - --- - -- - - - - - - - - - -- - -

Composita subtilita _______________________ ---- ________ X X ____ X X X --""'- ---------------------------- Composita sp .. ____ .;. _________________________ ---- ____________ --,.----.-- _____ X X --""'- ------------------------

Derbya crassa __________ .:.----------------- ---- ---- ---- ---- ---- ____ X ---·- __ ;.....,_ ---- ---- ---- ---- ---- ---- ---- ---- Lingula carbonaria ________________________ ---- ________ ---- _________ ___ ____ _ ---- ---- ---- X ---- ---- ---- ---- --.,.-

~~~;i~if:I in-g-;_.~ t~: : : : : : : .: : : : : : : : : : : : : : : : : : : : : : : : -X -: : : : : : : : : : : : : : : : -X -: : : : ~ ~ : : : : : : : : : : : : : : : : : : -~ -: ·= : : : : : = Marginifera ingrata var ____________________________ X ---- __ _: _________ --·-- ---- ---- ---- ---- ---- ---- ---- ---- ---- Marginjfera muricata __________________________________________________ --·-- ---- ---- X ---- ---- ---- ---- ---- --,...-

~r~~~~w:as~[;;~~~fe;_-si;~~===========~=== :::: ~ :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: :::: ==== :::: Orbiculoidea sp.? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X _ _ _ _ _ _ _ _ _ _ _ _ X __ -- ---- ---- ---- ---- ---- ---- ---- ---- ---- Productus coloradoensis ____________________________ X X ---- ____ X --·-- X · ---- ---- ---- X ---- ---- ---- ---- Productus cora ___________________________________ X X ---- ____ X X ----' X ---- ---- X >< ---- X _;... __ Produotus cora var. nodosus _______________________ X ____________ X >< ---- ---- ---- ---- ---- ---- ---- ---- ---- Productus aff. P. pertenuis _____________________________________________ >< ____________________ ":;:! ___ ________ ----

~~~~~~t~: ~p.?~~~~~~~-~e~~s~~~a-t~~~======== ::::::::::::::::_X_::::-~-:::: _X __ X_:::::::::::::::::::::::::::: 

Pustula nebraskensis _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X _____________ -.. - ---- ---- ---- ---- X ---- ---- ---- ---- Pustula nebraskensis var ______________________ ---- ________ -------- X --·-- ---- ---- ---- ---------------- ---- ---·-

Pustula n. SP----------------------------- ----------------------------- >< -------------------------------------
32 SHORTER CONTRIBUTIONs· TO GENERAL GEOLOGY, 1934-35 · 

Distribution by locality of fossils obtained from the Weber (?)formation-Continued 

885lc 685le 6852 6852a 6853 6854 6855 6855a 6856 .6857 6858 6860 6860b 6860c 6860d 6860e 6860f 

~---------------------1--- --------------------------------

BRACHIOPODS-continued 

Spirifer opimus _________________________________________ ________ _______ --~- X _______________________________ _ 

~~~~~~:~~~~~~: Spirifer ~:~--~~~i~~~~~~i~======= ==== ~ ==== ==== ==== ==== ~=:':= == .-x- ==== ==== ==== ==== ==== -~- ==== ==== -~- ==== rockymontanus ____________________________ X X ___ _ _____ ___ ___ _____ ---- ---- ---- ----- ---- ---- ---- ---- Spirifer sp _____________________________________ ___ ____ ._ __ X ________________ ------------------ -------------- Squamularia perplexa?_ ___________________ ______ __________ X ___ ___ _______ __________________________________ _ Squamularia sp ___________________________________ _____ _______________________ X ___________________________ _ 

Strophalosia spondyliformis _____________ ~-- ____ ____ ____ ____ _______ _____ X ___________________________________ _ 

. ' 

PELECYPODS I 

i~lffim~~~f~f~;~~;~-~~~ =~~~=~~=~~~~~ ==~= ~~~t === ;~; ~~=~ ~~== :~: -~ ~~~ =~~= ~~(=~~ ~~~~ ~~~~ =~= ~~~; :~t~~ Leda f~~o~_d!;~:~~~======== sp.? _____ _ _ _ _ _ _ _ _ ================= _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ==== _ _ _ _ _ === _ _ ==== 

_ _ _ _ === _ _ _ _ ·= ==== 

_ _ _ _ _ _ ==== _ _ ==== 

_ _ _ _ _ _ _ _ _ _ _ ==== ==== _ _ _ _ _ _ ==== ==== _ _ _ ====-~--X-============ _ _ _ _ X _______________ _ 

Lima sp.? _______________________________ ~ ________ X · ____ X ________ ---- ____ -------------------------------- Myalina perniformis __________________________ ---·- ____ · X ________________________________ X _______________ _ 

Nucula sp.? ______________________________________________ X ________________ -------------------------------- Pleurophorus subcostatus? _________________________________________________ X ____________________ -- r - _______ _ Schizodus sp.?_ ______________ ________ ___ ________ ______ _____ _____ ______ __ __ X ________________ X __ _________ _ 

Y oidia glabra _______ ________ __ __ __ ____ -.- _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X ______ __ _______________________ _ 

GASTROPODS 

Aclisina (4 n. sp.) _____________ _______________ _ ---~ ________ X ___ _____________ ____________ ------------ ~--- ---- Bellerophon crassus _____________________ __ ________________ X __ __ ______ _____ __ _______ ------------------------ Bellerophon n. sp ________________________________ _ __ ____________ _________ _ ______ __ ____________ X ___________ _ Bellerophon sp.? _____________________ ____ _______ ______ ___ _ X ________________ X ___________________________ _ . Bucanopsis sp.? ___________________________________________________ , ________________________ X _______________ _ Bulimorpha sp.? ____________ __ ______________ _______ ___ ___________ . _____________ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X ___________ _ 

Bulimorpha n. sp __________________________________ ____ ___ X ____________________________ ---- ---- ---- -------- Cyclonema n. sp _____________ ______ _______________________ X __ ____ ____ ______________ ------------------------ Enchostoma sp.? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X ______________ -- ---- ---- -- -- -- -- ---- ----

Euphemus ~~~~t!~~u~a;b~niri~;~=================== nodicarinatus? ____________ _: ______==== ___ === ___ = 

__==== ______ ==== _________ -~- ========-X-=============================== __ _______ _____ ____ ______ X _______________ ·[ ==== _ Gastropod fragments ____________________ __ X ____________________________________________________________ X 

Goniospira sp.? ____ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X ______________________ -- ---- ---- ---- - --- ---- ----

Meekospira sp.? ------------------ -------- ________ X ____ X _______ _ ----·---- ________ -------- --- - ---- -------- Microdoma 2 n. sp ____________ _____ _______________________ X _______ _ ____________________ -------------------- Naticopsis 5 n. sp _________________________________________ X ________________________ ---- ---- ~- '---- ---- ----

~~~~~fi~~j~~~i~~~~~:::~:~~ Pharkidonotus percarinatus _____ ____

~~~~____

:~:~~= ___ ~~~~ _____________________ ~~=~ =~= ~~=: :~f:: __ _____

~==~ __

~~~-______________________ ~~ -~~ ~~: =~=~ ~~~= ~~~= :~; X ~~~= ____ ~=~= ~--

:=~: ___ _ Placunopsis sp _________ ___ . ___________________________________________________________________ X _______ :_ ---~ 

Plagioglypta sp.? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X ___________ _ 

~~:~~~~~~:~~: Schizostoma catilloides ;p~?_s_~~==================== ____________________________________ ==== ==== ==== === ~ Q X ==== 

____________________________ ==== ==== ==== ==== ==== ==== ==== X === _______________ = == == ==== =~= _ Sphaerodoma primigenia_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X ___________ _ 

Sphaerodoma sp.? __________________ ·- _ _ _ _ _ _ _ _ _ _ _ _ _ X _ _ _ _ X ______________________ -- ---- ---- ---- ----- ---- ---- Trachydomia 2 n. sp _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X _______________________ '" __ - _____ - - - - - - - - - - - - - - - -

Dentalium ~~~cil!~y;~:~~i~1~ sp.?_ _______________________________________________________________________________ ~ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -x -= = = = _ ~ _ = = = : = = = = = : = = = = = = = = = = = = = = = = = = = = = = _ ~ X _ = = = = = = = ~ : = = : It ____ ~--- ___ _ 

CEPHALOPODS ,~ I 

'I 

g~t~~~~~e;s Protocycloceras sfr;:?~=============== sp.? _ _ _ _ _ _ _ _ _ _ _ _ _ 

===_ _ _ _ _ _ _ ====_ _ 

== _ ==== 

_ _ _ _ ==== 

_ _ _ _ -~-X ==== 

_________________________________ ==== ==== ==== ==== -x- ==== ==== =·=== ===: ==== ==== ==== "'x- _ :.- - _- _ ---- ---- ---- ----

CRUSTACEANS t 

Estheria aff. E. ortoni_ _____________________ ____ _____________________________ · ___________ X ___________________ _ 

Phillipsia sp.? ________ -·- _____ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X _ _ _ _ _ _ _ _ X ___________ ~ __ -- ---- ---- ---- ---- ---- ---- Trilobite fragment ________________________________ X -'"-- ____________________________ -------- ---- -------- --~-

. VERTEBRATES , 

~-

~~hr~~~~~~ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = J = = = = = = = = = = = = = = = = -X - = = = = = = = = = = = = = = = = = = = =I= = = = = = = = = = = = -~ -·= = = = = = = ·= -~ - ::h 1

1, 
PALEOZOIC , FORMATIONS , OF THE :MOSQUITO JtANGE, ·COLORADO 33 

685l=J-6. Horseshoe section ·(bed 8); pill north and northeast of old town of Leavick. 

6851a=J-7~ Horseshoe section (bed 13), hill north and northeast of ·old town of Leavick. 

.6851b==;:J-8 .. Horseshoe section (bed 25), hill north and northeast of old .to:w:n of. Lea vick. 

·6851c=J-9. Horseshoe section (bed 28), hill rrorth and northeast of old town .of Leavick . 

.6851d7=J-10. Horseshoe section (bed 30), hill north and 

northeast of old town of Leavick. 

6851e=J-11. Horseshoe section (bed 45); hill north and 

. northeast of old town of Leavick. 

6852=J-12 . . Ridge south of the Horseshoe cirques, near top 

about 150 feet above porphyry. (Same bed as J-7.) 

6852a=J-18. Same as. J-12 but stratigraphically about 50 

feetlligher. (Same bed as J-8.) 

6853=J-19. Hoosier Ridge, about 2 miles north of Hoosier 

Pass. Represents a horizon just about at the .boundary be-

. tween the Weber (?) and Maroon formations. (Gastropod 

fauna mostly new.) 

6854=J-37. Pennsylv~nia Mountain section (bed 50), on 

sharp crest on west end. (Alma district.) 

6855=J-41. Empire section (bed 12), south side of Empire IDll. 

(Leadville district, south end, about 200 feet, above fault.) 

6856 = J-45. Evans Peak section (bed 46), .at top of Evans 

Peak, shoulder below monument. 

6855a=J-50. Empire section (bed 14), locality 'same as J.;..41 

but about 70 feet higher stratigraphically. . 

6857=J-51a and J-52a. Jacque Mountain, about 3 miles 

west-northwest of Kokomo; from the Jacque Mountain limest?ne (top bed of Emmons' Maroon formation). Probably PermJ.an. 

6858=J-53. Ridge south of Jacque Mountain and west of 

Kokm_no (Tenmile quadrangle). Horizon uncertain, suppos-ed 

to .be m the Maroon formation. 

6859=J-60. Cliffs north of the Eagle River about threefourths. of a mile below Minturn, Eagle County, Colo. Somewhere in the Maroon formation. 

.6860=J-74. Trout Creek section (bed 32, center). Along 

Trout Creek about 1~ miles from old Colorado Fuel & Iron Co.'s 

quarries, in valley bottom west of road. 

6860a=J-75. Trout Creek section (bed 32, top). 

6860b=J-77. Trout Creek section (bed 43). ~arne locality 

as J-74-75 but 124 feet higher stratigraphically._. 

· 6860c=J-78. Trout Creek section (bed' 4S). Same locality_ as 

J-77 but about 70 feet higher stratigraphically. 

6860d = J-84. Trout Creek section (hed 89). 

6860e=J-85. Trout Creek section (bed 99). 

6860L=J-86. Trout Creek section (bed 91). 

Correlation.-The fossils obtained indicate that the 

lower and middle zones of the Weber (?) formation 

are of Pennsylvanian age and equivalent to the middle 

Pottsville and part of th~ upper Pottsville of the East. 

No equivalent·of the lower part of the Pottsville was 

. observed. ' · 

In Colorado the Weber (?) formatio~ is the equivalent of the Lower Sang:r;e de Cristo of the Sangre de 

Cristo region, a portion of the Hermosa formation of 

southwester~ Colorado, and at least some of the lowest 

part of the Fountain formation of the Colorado 

Springs region. It is also equivalent to . part of -the 

Magdalena formation of northern New Mexico. 

· Detailed sections.-Except where otherwise· noted 

the sections given below were measured by the writer 

and his assistant, Mr. C. D. Hier. The exact method 

used differed somewhat in different sections. Wherever 

possible the work was done with a tape on steep slopes 

and cliffs. Where the slopes were gentle or there were 

large covered p,reas transit and stadia were used. On 

the longer sections the tape results were -checked by 

surveying methods. 

Section on London Mountain 

[Section in lower part of the Weber(?) formation on London Mountain, commencing 

at sadd~e west of North London mine. Includes the lower zone and about half of 

the middle zone. Section measured up the crest to the southeast along London 

Mountain to the London fault] · 

Pre-Cambrian. · Fault contact. 

93. Quartzite, badly shattered ______________________ _ 

92. Shaly sandstone ___________________ ~ ___________ _ 

91. Brownish-gray limeotone _______________________ _ 

90. Coarse light-gray grit_ _________________________ _ 

89. Porphyritic quartz moPzonite dike _______________ _ 

88. Quartzite and grit _____________________________ _ 

87. Conglomeratic sandstone __ ~- ____ ~ ___ .:. __________ _ 

86. Sandy shale ______________________ ~ ___ ~ _______ _ 

85. Light-gray conglomeratic grit_ __________________ _ 

84. Red shaly sandstone ___________________________ _ 

83. Conglomeratic sandstone _______________________ _ 

82. Thin limestone. Weathered into small brown 

pieces. Contains abundant fragments of crinoid 

stems, a few bryozoans, pieces of brachiopod 

shells and an orbiculoidea (J-17) ______________ _ 

81. Black papery shale ____________________________ _ 

Feet 

55.0 

5. 0 

6. 0 

35. 0 

20. 0 

65.0 

35.0 

8. 0 

75.0 

5. 0 

85. 0 

6.0 

6. 4 

80. Gray conglomeratic grit with numerous small quartz 

pebbles_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 30. 2 

79. Dark reddish brown, sandy, micaceous shale. Small 

fault about 6 feet displacement________________ 26.0 

78. Conglomeratic grit, light gray, airpost white. 

Abundant quartz pebbles_____________________ 11. 0 

77. Gray sandstone with interbedded red sandy shale_ 8. 1 

76. Red sandy shale, slightly micaceous_ _ _ _ _ _ _ _ _ _ _ _ _ _ 5. 1 

75. Gray grit. .Numerous quartz pebbles up to 1 inch 

long. Poorly crosJ-bedded. Just below top 

pebbles increase in size to about 2~ inches______ 34. 0 

74. Gray sandy shale, slightly micaceous______________ 3. 0 

73. Coarse 1\gh~-gray grit yvith small quartz pebbles____ · 5. 0 

72. Badly shattered material. Fault with iron-stained 

fiJ?-e ~atJ:rial aiong its trace:.. __ ~ ______________ _ 

71. Gray s'aridstone ____________ ~ __________________ _ 

70. Gray shale,· with limy concretions ________ ~ ______ _ 

69. Gray quartzite ________________________________ _ 

68. Black papery shale, slig;h.tly micaceous ___________ _ 

67. · Gray quartzite_ ~_ ' ___ ,.~ ~ ______________ ~ ____ ~ ___ _ 

66. Gray sandy shale; weathers light brown __________ _ 

6.5 .. Hard gray sandstone ___________________________ _ 

64·. Dark-gray sandy limestone; weathers _brown_:_ _____ ' 

40. 0 

12. o· 

6. 2 

3. 5 

1.0 

5. 1 

6. 4 

'10. 1 

3. 0 

63 . . Light brown..:gray shale containing abundant 

' rounded p1eces' of brown limestone_:'------------ 9. 2 

62 ... Gray fine-gniined quartzite __ ~ ____ · ___ ,__ ___ _______ 8. 0 

61. Black, impure lim13sto:n,e, · ~odiilar; contains carbon~ 

aceous partic,~es_ _, ;::- _ _: .,.'.:__ _______________ ~-

60. Yellowish -gray fda ble sand,ston~ :nodular toward t.<?P _ 

59·. Dark..:gray · qu~r.tzite __ ~ :.:;:- --.--:- ~ ~ __ ~ _ ~ __ -: ·- _____ .,. _ 

58. Sandy, slightly micaceous shalE\ _ _: ___ :.. ______ .:._~--

5. 5 

6. 5 

4. 6 

1.7 

57. Limy shale grading upward!nto riodula~ lime~tone; 

weathers' brown ____ -------------------------- 4~ 7: 

56. Dark-gray quart2!ite, weathering brown___________ 4. 5 

55. Dark-gray thin-bedded sandstone with shaly.bedding_ planes ________________________________ _:_: ___ _ 5. 0 

:. 

54. Dark-gray to black sandy ·shale. A little fine..: 

grained mica _______________________________ _ 2. 1 
ll 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1934-35 

Section on London Mountain-Continued 

53. White conglomeratic quartzite. Abundant quartz 

pebbles as much as 1% inches across ___ ~--------

52. Irregularly bedded dark-gray sandstones and brownish-gray shale __________________ · ___________ _ _ 

51. Light-gray to white conglomeratic grit. Contains 

abundant quartz pebbles as much as 2% inches 

across. Cross-bedded ___ ~ __________ -. ________ _ 

50. Shaly sandstone Jike that below fault ____________ _ 

49. Gray to brown shaly sandatone _________________ _ 

48. Dark-gray quartzite and fine-grained shaly sandstone-------------------------~------------- · 

Porphyry (quartz monzonite); irregular silL ______ _ 

47. Sandy shale like that under sill. Igneous rock 

apparently has wedged into the shale ______ -.- __ 

Greenish-white porphyry; about ___ _ ~ __________ _ _ 

46. Olive-brown altered ahale, alternating with thin 

sandstone and some brownish shale __ ~ ________ _ 

45. Black quartzite _________ __ ____________________ _ 

Porophyry (quartz monzonite) sill; about _________ _ 

44. Alternating quartzite and sandy shale ____________ _ 

43. Dark-gray calcareous sandstone, very calcareous at 

base. Weathers into peculiar pitted nodular 

brown pieces ___ __________________________ __ _ 

42. Gray sandstone _______________________________ _ 

41. Gray sandy shale, micaceous ____ _____ ___________ _ 

40. Gray quartzite ___ ________ ___________________ __ _ 

39. Gray impure limestone; weathers brown; contains 

amall angular particles of white quartz; becomes 

very sandy at top ______________ __ ___________ _ 

38. Black sandy shale_ "" _____ _____ __ ______ __ _______ -

37. Coarse sandstone with sandy shale break,. These 

beds are irregular and pinch and swell. Streaks 

of pebbles at base of some of the sandstone __ · __ _ 

36. Gray shale, slightly micaceous, sandy _______ _ _ 

35. Dark-gray quartzite ____________________________ _ 

34. Light-gray sandy shale ______ ______ _____________ _ 

33·. Coarse gray sandstone, with small quartz pebbles 

scattered through it. Rather massively bedded. 

Thin breaks of light-gray sandy .shale between some beds _____ ___ __________________________ _ 

Porphyry sill; about_ _____ ____ -' ________________ _ 

32·. Coarse sandstone, almost white; contains scattered 

quartz pebbles as much as 1% inches in diameter __ 

Several .small fault..;. Similar sequences of bed.s in 

the several blocks and on far side. Section continued beyond. 

31. Yellowish-brown sandy shale ____ ______ _________ _ 

30. Black quartzitic sandstone, massively bedded _____ _ 

29. Light-gray, limy, sandy shale; weathers tan ______ _ 

28. Dark-gray quartzite, shaly, coarsely ripple-marked bedding planes _____________________________ _ 

27. Light-brown to black sandy shale; contains some vegetable rna terial ______ ;- __________ :.. ________ _ 

26. Greenish-gray quartzite:.. _____ ,.. _________________ _ 

2~. Coarse white grit, with conglomerate streaks ______ _ 

24. Conglomerate. White quartz pebbles; some shaly 

pieces with an inky-black cement (pebbles 1 inch 

or less, shale pieces larger)--- ----------------

23. Black shale; contains abundant poorly preserved 

plant stems (J-15)--------------------------- 22. Sandstone, 6 inches to 2 feet thick _______________ _ 

Suggestions of a slight unconformity, as the limestone has an irregular upper surface; the sandstone 

is of variable thickness. 

21~ Black impure limestone; weathers rich brown _____ _ 

Feet 

8. 5 

15. 0 

13. 0 

4. 5 . 

1.2 

7. 5 

45+ 

2. 3 

3. 6 

6. 5 

3. 5 

10 

3 

2. 5 

2 

2. 8 

1.6 

3. 6 

2. 7 

4. 7 

1.6 

4. 5 

1.1 

17. 3 

25 

13. 1 

7. 0 

12. 9 

4 

1.5 

3. 3 

5 

12 

. 8 

1.5 

1.0 

3. 2 

Section· on London Mountain-Continued 

20. Yellowish-gray calcareous sandstone, slightly micaceous; weathers into nodular fragments. Crosses 

Feet 

a fault_________________ _____________________ 6. 1 

19. Black shaly sandstone_______ ___________________ 1. 7 

18. Dark-gray quartzite. Coarse ripple marks on top of 

layers. Massively bedded____________________ 5. 5 

17. Alternating gray quartzite and sandy shale________ 1. 4 

16. Black sandy shale; contains a little fine mica_______ 5. 1 

15. Black quartzite________________________________ 7. 1 

14. Brownish-black, sandy limestone, alternating with 

light-gray sandy shale. Limestone is probably 

somewhat dolomitic. Dark gray when fresh, but 

most of the material is brown. Top layer contains large irregular "ironstone·" concretions____ 11. 7 

13. Dark.:.gray to black gritty quartzite, hard, massively 

bedded. Along stratification planes are streaks 

of white quartz pebbles as much~. as five-eighths of 

an inch across and in a few places black micaceous 

shale streaks. Some shale fragments are included 

in grits (J-13)--------------- ~--------------- 8. 7 

12. Light-gray shaly sandstone, slightly micaceous, soft_ 4. 3 

11. Light-gray, almost white quartzite, massively bedded_ 7. o 

10. Light-tan sandy micaceous shale, fine-grained; contains nodules of siliceous material that weathers 

dark_____________________ __ ________________ 2.5 

9. Light- gray coarse- grained sandstone; weathers 

brown. Beds 6 inches to 2% feet thick______ ___ 12.0 

8. White to light"'gray quartzite; co~tains two streaks 

of black micaceous shale------~--------------- 3. 6 Porphyry __ : ___________________________________ 25.5 

7. Dark-gray quartzite, medium-grained, and hard grit, light brownish gray ___________ .;.______________ 1.·1 

6. Black sandy shale, carbonaceous, slightly micaceous_ . 5 

5. Dark-gray fine-grained quartzite_________________ 1. 3 

4. Black sandy shale, slightly micaceous; contains a 

few suggestions of plant fragments_- __ --------- 1. 0 

3. Gray quartzite, massively bedded, medium finegrained. Some white quartz pebbles, half an inch 

or less in size, along bases of so:me layers________ 18. 5 

Porphyry sill. Monzonite, light gray. A small 

fault 1pay occur, but there appears to be only slipping caused by a wedge-shaped sill. 

2. Gray quartzite, alternating with a black, highly carbonaceous sandy shale that has been baked until 

it has almost an anthracite luster. Some shale 

surfaces show pyrite in iridescent coatings. A 

few undeterminable plant fragments in shales_-__ 27. 3 

1. Dark-gray quartzite,hard, massiv~ly bedded, probably somewhat silicified by the underlying silL___ 7. 4 

Porphyry sill. 

The base of the formation 1s concealed, but outcrops 1n adjoining canyons indicate that there are 

about 60 feet of beds between the base of the section 

measured and the top of the Leadville. 

Section of lower part of Weber (?)formation at Evans Peak 

[About 3 miles east of Leadville, Colo., south of Mosquito Pass. All of the section is 

in the lower zone. Present erosion surface on top of the peak] 

Feet 

51, 50. White pebbly grit, some layers slightly micaceous. 

Pronounced cross-bedding _______________ ---_ 17 .. 0 

49. Dark-gray grit; contains pebbly streaks___________ 28. 3 

48. Dark-gray limestone; weathers brownish _______ --_ 11. 0 
\ 

PALEOZOIC FORMATIONS OF THE MOSQUITO . RANGE, COt.O:RAi>O 35 

Section of lower part oJ Weber (?) formation at Evans PeakContinued 

47. Dark-gray sandstone, somewhat gritty ___________ _ 

46. Dark-gray limestone; weathers brown; thinbedded, contains the following marine fossils 

(locality 6856): Cleiothyridina pecosi var., Composita subtilita, Composita sp., Chonetes geinitzianus?, 

Productus coloradoensis, Productus sp. ?, Spirifer 

opimus, Pleurophorus subcostatus?, Schizodus sp.?, · Yoldia glabra ___________________ _ ---'---- ____ _ 

45. Dark-gray shale ___ ~----------------------------

44. Massive light-gray grit ______________________ .... ! •.J ..: • 

43. Massive light-gray sandstone, with thin streaks of 

interbedded dark-gray shale. Both sandstone and 

Feet 

12: ·3 

8. 3 

9. 6 

31. 0 

shale slightly micaceous _______ ::_ .. :! _______ .:."l. !.f..: 1- 28. 1 

42. Sandstone, thin-bedded, slightly micaceous________ 2. 0 

41. Black sandy shale-------------------------- --- 1. 3 

40. Dark-gray)mpure limestone; weathers gray-brown~ ~· 2 

39. Dark-gray alternating sandstone and shale________ 12. 4 

38. Light-gray grit with scattered quartz pebbles i~ 

inches in size _______________________________ _ 

37. Alternating sandstone and shale-----------~------

36. Dark-gray shale ___________________ __ __________ _ 

35. Dark-gray sandstone; porphyry silL _____________ _ 

34. Alternating black sandstone and shale; porphyry 

sill (thin) _____ _____________________ .:. _______ _ 

33. Alternating gray sandstone and black shale _______ _ 

32. Dark-gray calcareous grit_ ____________ __ _______ _ 

31. Dark-gray sandy shale. Poor plant fragments ____ _ 

30. Light-gray fine-grained sandstone __________ .:. ____ _ 

29. Dark-gray sandy shale..: ________________________ _ 

28. Light-gray, almost white fine-grained sandstone, 

massively bedded _________________________ ~ __ 

27. Alternating thin limestone and black sandy, slightly 

micaceous shale ______________________ :.. ______ _ 

26. Coarse gray sandstone. Scattered quartz pebbles, 

three-quarters of an inch in diameter _________ _ 

25. Black flaky shale ______________________________ _ 

24. Massive light-gray sandstone ___________________ _ 

23. Black, slightly sandy shale_· ____________________ _ 

22. Massive dark-gray sandstone ___________________ _ 

21. Alternating black, slightly micaceous shale and thin 

dark-gray sandstone ________ ______ ___________ _ 

20. White to light-gray grit; contains numerous quartz 

. pebbles, 1 inch in diameter------ -------~-----

19. Dark..:gray, slightly micaceous shale ______ .: _______ _ 

18. Gray sandstone _______________________________ _ 

17. Dark-gray shale. Contains some beautifully preserved plants, especially ferns. The . forms collected from this layer arid from the black "slate" 

mentioned below (localities 8049 and 8083) were 

identified by C. B. Read. (Seep. 31.) _________ _ 

16. Light-gray sandstone, fine-grained _______________ _ 

15. Light-gray shale _______________________________ _ 

14 .. Light-gray sandstone, fine-grained _______________ _ 

13. Dark-gray sandy shale. Very friable at base ____ :.._ 

12~ Fine-grained white sandstone. Massively bedded __ 

11. Black "slate" with a -few interbedded sandstones; 

carries a few well~preserved plants listed on p. 31 

(J-43) ____ ;_ ________________________________ _ 

10·. Shaly sandstone, somewhat coaly_-_______________ _ 

~ Dark-gray sandstone; carries abundant poorly pre- · served plant stems _________ ___ _________ :.. ____ _ 

8: Black carbonaceous shale, somewhat sandy _______ _ 

7; White sandstone, massively bedded_T __________ ~ __ 

6. Black carbonaceous shale; contains much vegetable rna teriaL ____ ..: __ ..: _________________________ ~ _ 

5. Dark-gray limestone, fine-grained; weathers brown_ 

15 

21. 0 

4. 1 

2. 8 

15.0 

6. 1 

2. 3 

.8 

2. 5 

.4 

2. 8 

8. 8 

3. 4 

. 8 

3. 2 

1.0 

2. 5 

2.0 

-4. 1 

1.1 

1.8 

• •4 

5. 5 

. 4 

2. 5 

8. 8 

6. 4 

3. 9 

·2. 8 

3. 1 

2. 6 

12.0 

1.5 

2. 0 

Section of lower-part of Weber (?) formation at Evans Pea'k__:_ 

Continued · 

Feet 

4. Black slaty shale; contains numerous plant impressions. A few ferns obtained from this bed. About 

1 foot of coaly shale at top___________________ 4. 7 

3. Dark-gray shaly sandstone_____________________ 2. 6 

Mainly black shale, sorriewhat slaty. Sill several 

hundred feet thick ___ .:..-----------------~---- 25+ 

2. Some shale and sandy shales between sills ______ :-_ 50+ 

Sills 

1. Largely covered; appears to be mainly or entirely 

black shale_________________________________ 35 ± 

Unconformity. 

Leadville limestone 

Section of part of Pennsylvanian beds (Weber ? formation) along 

Trout Creek 

[Section commences at mouth of second gulch north of Colorado Fuel & Iron Co.'s 

old kilns, extends ·northeast for several hundred feet to a conspicuous limestone, 

follows it along the strike for nearly a mile southward, then extends perpendicular 

to the strike across the valley to a fltult, occasionally offsetting along the strike 

until better outcrops of overlying beds could be obtained. The· section starts at 

the base of the formation and includes nearly all of it. It would appear that the 

last beds obtained in the section are close to the base of the red beds, to judge 

by outcrops farther up the valley. . Some red beds appear among the gray farther 

up the valley but beyond some faults] 

Faults. Feet 

124. Crumpled and brecciated materiaL _________ ~___ 85 ± 

123. Thin sandstone and shaly sandstone; some cal- · 

careous streaks. Some layers show very small 

ripple marks. Material fine-grained__________ 60. 0 

122. Yellowish-gray sandstone, slightly arkosic, 

mainly thin-bedded--~---------------------- 41.0 

121. Sandy shale__________________________________ 22. 8 

120. Thin impure dark-gray limestone (J-96)_________ 4. 6 

119. Gray to greenish-gray sandy shale with a few thin 

.118. 

117. 

116. 

115. 

114. 

113. 

112. 

111. 

110. 

109 . 

108. 

107. 

106. 

105. 

104. 

103. 

102. 

sandstones. One sandstone contains black-shale 

pebbles____________________________________ 34. 5 

Gray calcareous sandstone, weathered brown ___ -. 1. 6 

Green-gray shaly sandstone____________________ 6. 0 

Gray impure limestone with numerous enclosed 

pieces of black shale as much as 3 inches across. 

Resembles a caliche conglomerate_____________ 2. 8 

Gray calcareous shale with streaks of limestone 

and black shale ____ -' _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 14. 0 

Slab by gray limestone ________________ ----____ . 8 

Black shale_ ..:.---- ~~ ------' ------------------- 5. 0 

Slabby impure limestone;eontains a few fine mica 

flakes _____________________________________ _ 

Sandy shale with interbedded slabby sandstone, 8 

inches or less thick _________ ----- __ ~..:--------

Gray, slightly · micaceous sandstone and shaly 

sandstone. A few streaks of shale. Sandstone 

medium to fine grained---------~------------

Gray slabby ripple-marked sandstone. Toward 

top becomes gritty and even contains streaks of 

conglomerate. The coarse material is arkosic 

with feldspar pieces as much as three-quarters of. 

an inch across and only slightly rounded ___ --

Gray shale_ -' _____________ _ ...: _:.. ____ - - - _ - ----- -

Gray sandstone, slabby, surfaces ripple marked; 

contains a few poor impressions of land plants __ · 

Gray to black shale with streaks of interbedded 

brownish limestone 4 inches or less thick _____ -_ 

Sandstone, thin·bedded, surfaces ripple marked __ 

Gray to black shale, with thin streaks of brown 

limestone _______________ -' _:.. _________ - ---- _-

Gray limestone·; weathers tan _____ .:.. _____ - __ ~---

Gray shale _____ .... -- ____ --- ____ -------_----~--

1. 3 

30.0 

34.0 

14.0 

3. 3 . 

2. 3 

68.3 

8. 2 

63.3 

1. 3 

5. fi 
36 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1934-35 

Section of part of Pennsylvanian beds (Weqer? formation) along 

Trout Creek-Continued 

101. Fine-grained gray-brown sandstone _____ __ _____ _ 

100. Black shale with small calcareous masses and some 

streaks of shaly limestone ________ ~----------

99. Gray limestone; weathers light brown; contains 

small fossils, probably algal tubes ____________ _ 

98. Gray calcareous shale ________________________ _ 

~7 . . Blacklimestone _______________ ______________ _ 

96. Black shale-----------~----------------------

95. Gray nodular limestone; contains abundant tubular_masses with concentric structure _________ _ 

94. Gray .sandy mudstone; contains some calcareous 

concretions_______________________ _ ______ _ 

93. Black shale ___________ ______________________ _ 

92. Gray nodular limestone; contains tubular masses 

with a concentric structure that suggest algae or replaced plant stems ______ _________________ _ 

91. Black shale. Lower portion contains calcified 

objects suggesting coprolites, also fragments of 

gastropods and Orthoceras (locality 6860f) _____ _ 

90. Yellowish chalky limestone; carries marine fossils: 

Polypora sp. ?, Productus cora, Spirifer opimus 

var. occidentalis, Aviculopecten scalaris (locality 6860e) ____________________________________ _ 

89. Black shaly limestone; carries small fossils-Lingulas and possible ostracodes (locality 6860d) __ 

88. Black shale; suggestions of small fossils _______ __ _ 

87. Greenish-gray shaly limestone _________ ______ _ 

86. Black papery shale ____ __ ______________ ______ _ 

85. Thin fibrous calcite bands half an inch to 3 inches 

84. 

83. 

82. 

81. 

80. 

79. 

78. 

7,7. 

76. 

75. 

74. 

73. 

72. 

71. 

70. 

69. 

68. 

67. 

66. 

65. 

64. 

63. 

62. 

thick, containing algae; two such bands 3 inches 

apart _________ _______ __________ ___________ _ 

Brown sandy shale, soft ______________________ _ 

Gray -calcareous shale ___ _____________________ _ 

I>ark-gray limestone _______________ ____ ______ _ 

Gray limy shale ____________________ _________ _ 

Sill, dark-green coarse-grained rock, about 20 feet 

thick. 

Calcareous shale ___ _____________________ _ ..: __ _ 

Black, slightly sandy shale ______ . ___________ · _. __ 

Black limestone _____________________________ _ 

Black papery shale __________________ _~ _____ _ 

Thin limestone and interbedded calcareous shale. 

Contains a few fossils-Lingula carbonaria and 

Estheria aff. E. ortheni (locality 6860) _________ _ 

I>ark-gray limestone, coarsely rippled surface ___ _ 

Black papery shale with interbedded limestone. 

Limestone beds average ~bout o·.3Joot thick and . 

are spaced about 2~ feet apart ___ ~ __________ _ 

I>ark-gray limestone; weathers brow:o.. Contains. 

numerous algal tubes---- - ----------:- ------- Black papery shale __________________________ _ 

I>ark-gray limestone ________ ___________ ______ _ 

Black shale _____ __ __________ ____ -----------

I>ark-gray nodular limestone; weathers brown __ _ 

Black shale with thin beds of gray calcareous 

shale here ~nd there_.: ___ ..: __________________ _ 

I>ark-gray limestone; weathers brown __________ _ Black shale _________________________________ _ 

Gr~ysandstone ___________________ __________ _ 

Gray shaly sandstone _________________________ · 

Brownish-gray medium to fine-grained sandstone. 

Slabby. Shows small cross-bedding. Contains 

fragments of land plants (calamite, etc.) in poor 

state of preservation, also small pieces of mica 

as much as an eighth of an inch across ________ _ 

Feet 

0. 8 

42.0 

4. 1 

4. 0 

2. 1 

6. 0 

.8 

2. 6 

19. 3 

. 7 

11.0 

2. 6 

1.3 

58.6 

.8 

14. 6 

1.0 

40. 0 

4. 7 

1.3 

4. 2 

1.3 

9. 2 

1.4 

5. 8 

4. 6 

1.9 

20. 1 

1.0 

6. 6 

.6 

2. 1 

1.6 

10. 0 

1.8 

5. 2 

2. 1 

11. 4 

7. 5 

Section of part of Pennsylvanian beds (Weber? formation) along 

Trout Creek-Continued 

61. Sandy shale, soft, brown _____________________ _ 

60. Gray calcareous shale (J-80)---------------- --- 59. I>ark-gray limestone ______ ___________________ _ 

58. Gray calcareous shale _______________________ -_ 

Sijl; dark green coarse-grained rock about 20 feet 

thick. 

57. Gray calcareous shale ________________________ _ 

56. Black shale, slightly sandy ___________________ _ 

55. Black limestone _____ ·- ______________ ______ - _-_ 

54. Black papery shale _______ ___________ ________ _ 

53. Thin limestone with interbedded calcareous shale .:. _ 

52. I>ark-gray limestone, surface coarsely rippled __ __ · 

51. Shale, partly covered __ .. ____ _________ ___ ______ · 

50. I>ark-gray limestone ______________________ ___ _ 

49. Blac·k shale with thin limestone streaks _______ .:._ 

48. Thin limestone (beds average 2 inches) with interbedded shale. One very fossiliferous shale 

yielded crinoid stems, Rhombopora lepidodendroides, Productus cora, Deltopecten sp. ?, Placunopsis sp.?, Leda, n. sp., Schizod'us sp., Bellerophon n. sp., Patellostium n. sp., Plagioglypta sp. ?, 

Bulimorpha sp., Pharkidonotus percarinatus, 

Sphaerodoma primigenia, Zygopleura sp.?, Dentalium sp. ?, Aclisina sp., and coprolites (locality 

6880c) ------- ---------- ---------- --------- 47. Black carbonaceous shale ____ _________________ _ 

46. Gray limestone, thin-bedded _____ _____________ _ 

45. Black papery shale __________________________ _ 

44. Calcareous shale with thin limestone ___________ _ 

43. Gray limestone; w~athers platy. Fossiliferous, 

yielding crinoid stems, Septopora, Productus cora, 

Productus coloradoensis?, Pustula nebraskensis, 

Spirifera opimus var. occidentalis, Edmondia sp. ?, 

Leda sp.?, Mylina perniformis, Bucanopsis sp.?, 

Euphemus nodicarinatus?, Schiwstoma catilloides 

(locality 6860b) ·--- _______________________ - -

42. Black carbonaceous shale _____________________ _ 

41. Gray limestone __________ :. ___________________ _ 

40. I>ark-gray shale with numerous thin streaks of 

brownish-gray limestone ____ ________________ _ 

39. Black limestone __________ ____ _______________ _ 

38. Gray shale ___________________________ - _---- _ 

37. Brown limestone; contains shale fl.akes--------:--

36. I>ark-gray s~ndy limestone; contains a few very fine mica flakes _________ _______ ____________ _ 

35. Gray shale, becoming jet-black toward top _____ _ 

34. Black limestone, thin-bedded, slightly fossiliferous; 

contains a few marine fossils ____________ ____ _ 

33; I>ark-gray, somewhat calcareous shale ________ -_ 

32. Brown shaly limestone, very thin-bedded. One 

layer near middle largely of algal origin. Carries 

fossils in center. Top layer is chocolate-brown; 

contains small pelecypods __________________ _ 31. Black shale _________________________________ _ 

30. Black limestone; weathers nodular _____________ _ 

29. I> ark-gray shale-: _________________________ -_--

28. Slabby greenish-gray limestone with clay pebbles and shell fragments ____________ .:. ________ __ _ _ 

27. Light-gray shale ________________________ ..: ___ -_ 

26. Nodular limestone ___________________________ _ 

25. Covered, probably gray shale _________________ _ 

24. Gray laminated limestone ____________________ _ 

23. Gray shale _________________________________ _ 

22. Gray limestone, very thin-bedded, almost slaty __ 21. Covered (appears to be shale) _________________ _ 

Feet 

40. 0 

4. 7 

1.3 

4. 2 

1.3 

9. 2 

1.4 

5. 8 

4. 6 

1.9 

4. 5 

.. 9 

11. 0 

12.0 

14. 0 

1.4 

. 24.0 

29. 1 

1.8 

11. 3 

.8 

65. 5 

1.6 

3. 0 

.8 

2. 1 

28.6 

1.3 

4. 1 

5. 0 

58. 1 

3. 9 

65. 6 

2. 6 

3. 0 

.8 

15. 1 

2. 0 

7. 2 

3: 7 

125. 4 
PALEOZOIC FORMATIONS OF THE MOSQUITO RANGE, COLORADO 37 

Section of part of Pennsylvanian beds (Weber? formation) along 

Trout Creek-Continued 

Feet 

20. Gray limestone; contains fragments of marine fossils_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 4. 6 ± 

19. Covered; apparently shale with a few thin beds of 

limestone. No suggestion of sand in soil or float ______________ - ____________ ___________ · 223. 7 

18. Gray limestone; contains a few small angular 

quartz pebbles _____________ _____ .:. __ ______ ___ 1. 3 

17. Covered ___________ __ __ ______________ ______ __ 43. 1 

16. Dark-gray limestone_______________ ________ ___ 1. 0 

15. Covered ____________ _______ __ _____________ ___ 28.0 

14. Limestone; some interbedded shale. One t hin 

limestone bed has structure and markings suggestive of algae in roselike beads a quarter of an 

inch or less across. Other layers have small rodlike forms ________________ _______________ ___ 12. 8 

13. Covered (probably shale) ___________________ __ _ 18. 6 

12. Black limestone, massively bedded__________ __ _ 5. 4 

11. Basic sill _____ ______________ ______________ ___ 4. 0 

10. Shale with thin stre~ks of limy shale and a few thin 

beds of fine-grained sandstone. Sandstone surfaces show ripple marks that suggest shallow water ____________________ -- ______ __________ 75. 0 

9. Black limestone, massively bedded__________ ___ 1. 6 

8. Black shale; contains fragments of lepidodendrons 

and silicified masses of what appear to be large 

logs poorly preserved, showing several coats of 

bark. Logs at a definite horizon about 14 feet 

above base _________________________________ 21. 0 

Porphyry, about 35 feet thick. 

7. Covered, probably shale or sandy shale _________ 98. 2 

6. Gray limestone, thin-bedded; somewhat shaly; 

contains numerous fragments of Pennsylvanian 

fossils __________ __ - ____ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1. 8 

5. Covered _____ ____ __ ________ __ __ _____________ .:. 14. 0 

4. Gray sandstone, fine-grained ______ _.:.__________ 6. 2 

3. Covered--------~ --------------------------- 11:4 

2. Friable sandstone, gray but locally ferruginous 

and dark gray to red____ ____________________ 2. 4 

1. Covered_____________________________________ 6. 0 

Top of tBlue limestone; upper layers considerably 

impregnated with limonite. · 

Section of part of Weber (?)formation on Windy Ridge 

[Outcrop on east side of Windy Ridge about halfway between end and Dolly Varden 

mill, north of Alma, Colo. Taken only to show character of material. Thicknesses given are only approximate. Section starts about the middle cf the formation] · 

Porphyritic quartz monzonite. Feet 

16. Grit-------------------------~---------------- 45 

15. Fine-grained micaceous black sandstone (J-23) _ _ _ _ _ 17 

14. Light-gray coarse arkosic conglomerate grit________ 38 

13. Dark-gray fine-grained micaceous sandstone (J-24) __ 6 

12. Grit, black at top, becoming light gray at · base. 

Congiomeratic pebbles (averaging 1 to 1% inches) 

of quartz, feldspar, and schist and some pieces of 

black shale (J-25)----------------------- ----

11. Light-gray slaty micaceous,sandstone (J-26) ______ _ 

10. Grit, greenish gray when fresh; becomes light reddish brown on weathering. Is highly arkosic. 

General run of grains three-sixteenths of an inch 

or less, but pebbles as much as 4 inches in diameter 

occur singly or . in streaks through it. For an 

arkose these materials a re unusually well cemented 

(J-27) --------------------- _·_--- ------ ----

9. Dark-gray to black sand_stone, very micaceous on 

ar:td parallel to bedding planes (J-28) __________ _ 

45 

4 

70 

12 

Section of part of Weber (?)formation on Windy Ridge-Contd. 

Feet 

8. Dark-gray limestone; weathers brownish. Hard 

and fine-grained. No fossils observed (J-29)___ 3. 5 

7. Gray micaceous sandy shale (J-30) _------------- _ 2 

6. Red micaceous sandstone, blending downward into 

a greenish-gray quartzose sandstone (J-31)______ 10 

5. Gray micaceous sandy shale (J-32)_______________ 1. 0 

4. Gray to black arkosic conglomeratic girt. Wellrounded pebbles as much as 3 inches in diameter 

.scattered through it (J-33)-------------------·-- 28 

3. Dark..:gray sandy shale; slightly micaceous_____ 2. 5 

2. Black limestone; weathers brown. Highly siliceous: 

Streaks of white chert in upper layers. Lower 

layers contain streaks of black shaly material, 

and a few layers contain what appear to be altered 

crinoid stems (J-34)--------------------'------- 15 

1. Dark-gray slightly arkosic grit. Some layers moderately micaceous (J-35) -------- _ ---- -~ ------ _ 32 

Below this horjzon all is covered by float and dense 

aspen thickets and other vegetation. 

Section of part of Weber (?) formation at Horseshoe Mountain 

[Uphill northward from old town of Leavick, following around hill and through first 

cirque. Section starts at base of the formation and includes all of the first two 

zones and part of the upper zone] 

Covered with grass to big fault (about three-fourths 

of a mile). Only two outcrops in that interval. 

Each has a different dip and strike. 

95. Light-gray grits _______ ------------------------_ 

94. Dark-gray limestone; weathers brown ____________ _ 

93. Covered, mainly grass; a little sandstone float _____ _ 

92. Black shaly, very micaceous sandstone ___________ _ 91. Massive gray grit _____ ________________________ _ 

90. Dark sandy micaceous shale (soft)---- _- __________ _ 

89. Covered. Judging from talus it is largely coarse 

light-gray grit that weathers brownish. Much 

of it is micaceous ___________________________ _ 

88. Sandstone ____________________________________ _ 

· 87. Shale __________________ ------------_-----------

86. Sandstone ________ -------------------------.:---

85. Shale------ ---------------------------~------

84. Sandstone ______ -------------------""-----------

83. Shale ____________ - - - - - - - - - - - - - -- - - - - - - - - - - - c. - -

82. Gray sandstone, lenticular ____ -----------_-- ___ - - 81. Shale ________________________________________ _ 

80. Gray sandstone, lenticular ____ ----- ________ ---- __ 

79. Brown-gray papery shale ___ ---------------------

78. Brown shaly sandstone; looks calcareous _________ _ 77. Coarse gray grit _______________________________ _ 

76. Black papery shale, slightly micaceous ___________ _ 

75. Light-gray, almost white coarse granular sandstone; 

contains a little · silvery mica _________________ _ 

74. Dark-gray micaceous shale _________________ -- __ _ 

73. Light-gray coarse micac~ous sandstone ___________ _ 

72. Black sandy micaceous shale_.:. __________________ _ 

71'. Coarse gray micaceous sandstone; near the base 

Feet 

142 

6 

161 

42 

18 

33. 5 

172.5 

7. 4 

2 

6 

2 

6. 6 

3 

4 

2 

1 

1.2 

2 

3. 5 

2. 4 

19 

1.3 

7. 7 

1.5 

contains large fragments of black shale. The 

surfaces of some of the strata show coarse ripple 

marks, 7 to 8 inches across------------------~- 33 

70. 

69. 

68. 

67. 

Black sandy shale, carbonaceous_________________ 7 

Soft shaly micaceous sandstone, partly covered_____ 48 

Gray to white hard coarse sandstone, slightly to 

moderately micaceous; partly covered ________ -_ 67 

Covered. To judge from the float, it is all gray 

sandstone and grit. There' is c,onsiderable slickenside but appreciable faulting, as all slickenside is 

on bedding planes, and beds above and below seem 

to be c-ontinuous----------------------------- . 202. 5 
38 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1934-35 

Section of part of Weber (?)formation at Horseshoe MountainContinued 

66a. Black grit, mainly quartz with black cementing rna terial ____ ____________________ __________ _ _ 

66. Black limestone, weathering brown; dolomitic. No 

trace of fossils ______________________________ _ 

65. Black grit, mainly white quartz, some mica; cementing material inky black ______________________ _ 

64. Grayish-brown sandstone, .hard and coarse; considerable mica along bedding planes_-----------

63. Black to light-gray micaceous shale. Locally contains plant fragments, including small calamite 

stems------- ---------------------------~---

62. Gray sandstone, coarse, slightly micaceous ________ _ 

61. Gray-brown sandy micaceous shale _____ _________ _ 

60. Gray sandstone, hard, quartzitic ________________ _ 

59. Dark-gray · sandstone, calcareous and slightly micaceous, soft _________________________________ _ 

58. Dark-gray limestone, impure and very nodular. 

Many of the nodules are of pyrite that is weathering to limonite. Weathers brown _____________ _ 

57. Light-brown to tan calcareous shale, very fine grained _______ ___________________ ___ _______ _ 

56. Reddish-brown shaly sandstone, moderately mica- ceous _____ _______ ____ _______________ _______ _ 

55. Light-gray coarse sandstone or fine grit; weathers 

brownish, rriodera tely micaceous ___ _________ __ _ 

54. Gray, very sandy micaceous shale; weathers reddish brown ______ _____ __________ _____ ___________ _ 

53. Light-gray sandstone; some almost white. Fine to 

medium grained, slightly micaceous, rather thin 

bedded; shows poor cross-bedding _____________ _ 

52. Light-gray shaly micaceous sandstone ____________ _ 

51. White sugary sandstone, slabby at base and massive 

toward top. Shows good cross-bedding ________ _ 

50. White shaly sandstone __ ___________ _________ ___ _ 

49. Light-brown sandstone, massive and hard ______ -'-_ 

a:8. Light-brown sandy shale, slightly micaceous ______ _ 

47. Light-gray quartzitic sandstone, medium texture; weathers brownish _______ ______ __________ ___ _ 

46. Cream-colored, flaky, limy shale, slightly micaceous_ 

45. Black limestone (does not weather brown) hard and 

massive. Weathers into small irregular, angular 

pieces. At this locality it contains many small 

limonite stains that represent oxidized pyrite 

present in fresh material as small cubes. Contains numerous poorly preserved marine fossils, 

including crinoid stems, Marginifera aff. M. 

ingrata, and Orbiculoidea missouriensis (locality 

6851c). Near the top the limestone becomes 

slightly nodular and weathers more massively and 

brownish. Farther up the strike the pyrite and 

the slight metamorphism disappear ___________ _ 

· A small sill wedges in at this horizon a short 

distance down the strike from the place where the 

section was measured. 

44. Light~gray coarse sandstone; we'athers brownish. 

Lower portion massively bedded; upper portion 

somewhat slabby. A massive 5•foot bed on top_ 

43. Black limestone, thin-bedded to slabby; weathers 

brown, Upper foot becomes sandy and in places 

almost conglomeratic. The limestone con:tains 

poorly preserved marine fossils _______________ _ 

42. White grit, coarse, mainly quart:z, massively bedded_ 

41. Light-gray massive sandstone ___ ~ __ __________ ___ _ 

40. Light-tan sandy shale _____________ ____ _________ _ 

39. Slaty sandstone _____________________ .,. _______ __ _ 

38. Light-tan limy shale, hard ______________________ _ 

Feet 

12 

4.1 

29 

22 

1.5 

5. 5 

1 

1.5 

5. 2 

6. 4 

1.5 

2. 5 

45 

5 

27. 0 

8. ] 

26 

1.6 

1.3 

1.8 

1.9 

.5 

21. 7 

12 

10. 5 

1.4 

. 8 

1 

1.4 

Section of part of Weber (?)formation at Horseshoe MountainContinued 

37. Light brownish-gray sandstone, massively bedded, 

of medium texture ______________ -- __ -_----- __ 

36. White limy shale, hard but almost papery _______ _ 

35. Sandstone, fine quartzitrc, thin-bedded. Several 

streaks of white limy shale between sand beds_---

34. Black sandy limestone; weathers brown __________ _ 

33. White limy shale ___ ----- ____ ----- --- --------- __ 

32. Sandstone, massive, light brown (one bed), hard __ _ 

31. Limestone, almost white, very fine grained, slaty __ 

30. Very limy shale. Splits like slate. Fossiliferous; 

yielded Septopora sp.?, Productus cora, Deltopecten 

occidental is'!, Led a sp.?, gastropod fragments 

(collection 6851 d) __ - - - ___ - _ - _ --- - - - - - ------- _ 

29. Light-gray sandstone, hard and massive; contains 

considerable calcium-carbonate cement_ ___ ----

28. Dark-gray to black limestone, thin-bedded; weathers 

brown; contains fragments of fossils. One layer 

about the middle shows numerqus cross sections of 

small gastropods (collection 6851 c) _________ - __ _ 

27. Black limy shale; becomes less calcareous at top ___ _ 

26. Light-brownish sandstone, rather coarse grained 

and granular, massively bedded ____ _____ ______ _ 

25. Shaly limestone, very fine grained, almost white. 

Contains abundant Chonetes and some other fossils 

including Bryozoa, Orbiculoidea sp.?, Chonetes 

geinitzianus'l, Productus coloradoensis, Productus 

cora, Composita sp.?, Myalina perniformis, Yoldia 

n. sp.?, Leda n. sp., Parallelodon sp.?, Parallelodon carbonarius, Edmondia sp.? (collection 6851b). 

In spite of its thinness this bed i& a good horizon marker _______________ .. _______ _____________ _ 

24. Cream -colored massive sandstone ________________ _ 

23. Cream-colored thin-bedded sandstone _______ -_- __ _ 

22 . Black, slightly calcareous shale, very slightly fossiliferous ____ -_------------------- ---------_-

21. Sandstone, almost white, coarse-grained __________ _ 

20. Cream-colored shale, sandy and micaceous ________ _ 

19. Gray .sandstone, massive, hard __________________ _ 

18. Very light gray shale, limy, slightly micaceous ____ _ 

17. Dark-gray to black limestone _____________ .,. _____ _ 

16. Light-gray grit _____________ -- _____ --_----------

15. Nodular light-gray limestone, with some light chert ______________________________________ _ 

14. Lighter-gray shale, very calcareous; contains a few 

scattered fossils. Limy concretions (average 4 

inches long) abundant. At the top lies· several 

inches of limestone_- _- _ - ---------,.. - - - --- - - - - -

13. Black shale, slightly calcareous and very fossiliferous 

(Marginifera especially). The following fossils 

were obtained: Crinoid stems, bryozoans (Fenestella sp., Polypora sp., Rhombopora sp.), Composita 

sp.?, Derbya sp., Productus cora, Productus coloradoensis, Productus coloradoensis var., Productus 

sp., Pustula nebraskensis, Pustula nebraskensis'l, 

Marginifera ingrata, Marginifera muricata'!, Orbiculoides cf. 0. missouriensis, Spirifer rockymontanus, Acanthopecten cf. A. carboniferus, Deltapecten arkansanus, Leda bellastriata, Nucula'l sp., 

Yoldia sp., fish tooth (collection 6851a) ________ _ 

12. Largely covered. Apparently light-gray sandstone 

and fine grit. Som.e layers have white quartz 

pebbles as much as 2 inches across ____________ _ 

11. Sandstone, massively bedded, medium-coarse_.., ___ _ 

10. Largely covered, probably sandstone ______ ___ _ 

9. Light, gray sandstone, fine to medium texture, 

slightly micaceous, massively bedded_----------

Feet 

12. 5 

. 1.5 

4. 7 

1.2 

.5 

7. 3 

1.5 

9. 5 

2. 6 

. 2. 5 

6. 3 

8. 5 

4. 2 

2 

4. 0 

8. 6 

26.4 

. 8 

. 9 

.5 

1. 

1.5 

1.2 

5. 0 

13 

47 

106 

58 

18. 5 
PALEOZOIC FORMATIONS OF THE MOSQUITO RANGE, COLORADO 39 

Section of part of Weber (?) formation at Horseshoe MountainContinued 

8. Dark-gray fine-grained limestone, thin-bedded, 

slightly fossiliferous. Yielded Archaeocidaris, 

spines and plates (2 species), bryozoans, Produc-

·tus cora, Productus sp.?, (semireticularis type), 

Schizophoria texana?, Spirifer rqckymontanus, 

Deltopecten occidentalis, Pteria aff. · P:· ~h2~ensis, 

pelecypod fragments (collection 6851) ~ _. __ _ :. _-' __ 

· 7. Limy shale, blending upward in to limestone_ ~ ____ _ 

6. Coarse gray sandstone ______________________ :_ __ _ 

5. Gray shaly sandstone and shale, mostly fine-grained 

and slightly micaceous _______________________ _ 

4. Very light gray to dark sandstone and grit, rather 

thin::bedded, slightly micaceous. Some beds 

arkosic __________ .:_ _____ :.. __________ · _____ ._ · ____ _ 

3. White quartzitic santlstone ____ ----- ~~:.~· .~ ~~ ---~-

2. Shale, sandstone,· and grit (i10t very . coar~e), some 

sandy shale, light to dark gray, slightly micaceous. 

Feet 

11 

8 

8 

21 

27 

22 

Partly covered ___ ~- ___________ · ______________ ..: 57 

1. Yellowish:.tan limy shale .. --~ ---'----------------- 6 

Unconformity. 

Leadville limestone. 

Section of part of Weber (?)formation at west end of Pennsylvania 

Mountafn · 

[Section starts at top of porphyry in saddle at southwest corner of am pi theater. 

Follows along crest of ridge to London fault. Section starts almost at base of the 

formation and includes about two: thirds o{ itl 

Fault, 

133. Covered up to fault and badly fractured and displaced. There appear to be about 180 feet of 

strata, mainly sandstone and shale. Soine ·coarse · 

pebbly grit at toP---- ---------------------- 132. Light-gray grit ____ .:_ ______ ________ _: ___________ _ 

131. Gray sandy shale ____________ .:. ________________ _ 

130. Gray limestone; weathers brown ___________ _~ __ _ 129. Black grit ___________________________________ _ 

128. Black arkosic grit, pebbles as much as 5 inches 

across. Coarse feldspar fragments among th~ pebbles __________________________ , ________ _ 

127. Brown sandy shale _____ __________________ ____ :.. 

'126. Gray-black sandy shale _________________ ::~_~ __ ·.:. 

125. Gray limestone; ""eat]fers bro~n _______ ~ _ ~-:: _____ · 

124. Gray limy share; weathers brown ___ _: ______ ~-----

123. Light-gray shale -----_--~ _______ --:- ____ .:_~- -_ 

122. Limestone ____ ..:_..: _______________ ~ ______ ~.:. · __ · __ _ 

121. Gray sandy micaceous shale _____________ · ______ _ 

120. Limestone grading upward into sandstone_~------

119. Limestone __ ~ _____ ~ ____ · ______________________ _ 

118. Light-gray shale ___________________ -___________ _ 

117. Dark-gray grit_ ____________ 7

_-: __ .:_ ____________ _ 

116. Dark-:gray sandstone and shale .:._~_ .: ___________ _ 

115. Dark-gray sandy limestone, thin~bedded; weathers 

brown ______ . ______ .:. ____ ~- __ "".:. __ .:. _____ · ____ -__ _ 

114. Dark-gray sandstone:. __________ -______ -'--- ___ ~ __ · 

113. Light-gray sandy shale.:. ______ ~ ___ -- ~ _________ _ 

112. Dark-gray grit __________________________ ._· ____ _ 

111. Sandy micaceous shale, with a few thin sandstone 

layers near top~- ____________ · _____ ~- __ --~- __ _ 

110. Dark-gray sandy grit ______ ..., - ______________ -~-~_ 

A small fault cuts through at this place, but the 

same bed was picked up on the other side and the 

· section continued. 

109. Gray to brown sandy shale ___________________ _ 

108. Gray-brown fine-grained ·sandstone ______________ _ 

107. Gray to black shale, some slighly micaceous ____ _ 

Feet 

180 

35. 8 

' 12. 1 

9. 0 

15 

5. 6 

4. 9 

5. 0 

·. 8 

2. 7 

1. 1 

.7 

1.3 

1.4 

.8 

1.4 

4. 0 

2. 5 

3. 0 

1.8 

3. 0 ; 

104.0 

8. 3 

3. 7 

4.3 

2. 4 

4.6 

Section of part of Weber (?)formation at west end of Pennsylvania 

Mountain-Continued 

106. 

105. 

104. 

103. 

102. 

101. 

' 100. 

99. 

98. 

97. 

Gray limestone; weathers brown ________________ _ 

Light-gray grit ______________________________ _ 

Micaceous sandstone, fine-grained, thin-bedded __ 

Dark-gray grit, highly cross-bedded (short-length 

cross-bedding)---------------~--------------­

Light-gray, almost white grit, highly cross-bedded; 

pebble streaks near top ______________________ _ 

Black micaceous shale _____ ·- __________________ _ 

Gray micaceous sandstone _____________________ _ 

Light-gray shaly sandstone with streaks of tan 

shale---------------------------------------

Light-gray pebbly sandstone. Pebbles small but 

abundant. Numerous flakes of mica __________ _ 

Light-gray shale with thin interbedded sandstone. 

Both contain considerable mica. Mica scattered 

through the shale but concentrated mainly on 

hedding planes of tbe sandstone ______________ _ 

Tan-gray shaly sandstone. Thin-bedded. 

96. Dark-gray sa;ndy shale ________________________ _ 

95. Dark-gray grit_ ______________________________ _ 

94. Black sandy micaceous shale ___________________ _ 

93. Dark-gray sandstone __________________________ _ 

92. Black sandy micaceous shale ___________________ _ 

91. Gray sandstone, slightly pebbly. Surfaces of some 

beds marked with 4-inch ripples _________ ____ _ 

90. Dark-gray shaly sandsto:..1e ____________________ _ 

89. Dark-gray grit, hard __________________________ _ 

88. Black shale ("slate"); contains a number of markings suggestive of roots of land plants ________ _ 

Porphyry about 40 feet thick, but thickness differs 

along the strike. 

87. Dark-gray pebbly grit; contains a few thin streaks 

of black micaceous shale near base ___________ _ 

86. Light-gray coarse grit; contains mica in noticeable 

amounts, some pieces three-eighths of an inch 

across. Some layers slightly pebbly __________ _ 

85. Light-gray dandy shale ________________________ _ 

· 84. Dark-gray quartzite __________________________ _ 

83. Light tan-gray sandy shale, slightly micaceous __ _ 

82. Dark-gray quartzite ________________________ ;_ __ 

81. Light-gray pebbly grits, slightly · cross-bedded. 

Pebbles almost all of white quartz ____________ _ 

80. Papery black ehale ___________________________ _ 

79. Dark-gray pebbly sandstone ___________________ _ 

78. Coarse gray grit, some layers near ba.se almost a fine 

conglomerate; coarsely cross-bedded __________ _ 

77. Yellowish-gray sandy shale; contains a noticeable 

amount of very fine mica--------'------------

76. Dark-gray, almost black, cross-bedded; contain~ 

streaks of pebbles, also streaks of fine sand ____ _ 

75. Light-gray sandy shale, slightly micaceous ______ _ 

74. Yellowi-sh-gray micaceous grit ______________ --_-_ 

73. Gray sandy shale ___ :_ _________________________ _ 

72. Yellow-gray grit, slightly micaceous ____________ _ 

71. Red sandy shale, slightly micaceous ____________ _ 

70. Light-gray grit, cross-bedded; contains a few scattered quartz pebbles ________________________ _ 

69. Light-gray micaceous sandstone ________________ _ 

68. Yellow-gray soft sandstone, slightly shaly; contains a little mica _______________________________ _ 

67. White grit, massively bedded __________________ _ 

66. Light-gray quartzite, almost white. Beds about 

10 inches thick. Surfaces coarsely ripple marked_ 

65. Yellow sandstone _____________________________ _ 

64. Red sandy sha1e ______________________________ _ 

Feet 

1.8 

6. 2 

3. 1 

15. 5 

31. 8 

1. 1 

:4. 2 

4. 2 

4. 1 

3. 4 

7. 3 

5. 2 

.8 

1.3 

2. 8 

31. 5 

4. 2 

12. 3 

1.2 

12. 0 

6. 3 

1.2 

1.6 

.8 

2. 0 

14.0 

4. 2 

2. 1 

11. 2 

8. § 

68. 4 

3. 6 

1.8 

4. 6 

3. 1 

7 

8 

4. 2 

2. 8 

11 

5 

2 

3. 8 
40 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1934-3[) 

Section of part of Weber (?)formation at west end of Pennsylvania 

Mountain-Continued 

63. Brownish-gray coarse grit ______________________ _ 

62. Red and gray sandy micaceous shale ____________ _ 

61. Coarse white grit, madsively bedded ____________ _ 

60. Yellow sandstone _____ -------------------- ____ _ 59. Red sandy shale ______________________________ _ 

58. Dark-gray sandstone beds, about a foot thick. 

Surface of layers marked with ripples about 5 

inches across---------- ---------- ---------

57. Brownish-gray shaly sandstone, slightly micaceous_ 56. Red shaly sandstone ___ ______________ ..,; _______ _ 

55. Yellowish-browR sandstone_----- _____ ___ - - ----_ 

54. Dark-gray pebbly grits with some interbedded gray quartzite ___________________________________ _ 

53. Light-gray pebbly grit; shows good cross-bedding_ 52. Soft yellow sandstone _________________________ _ 

51. Green-gray quartzite __________________________ _ 

50. Calcareous shales grading upward into impure limestone. Weathers into small angular and concretionary pieces. Fossiliferous; contains crinoid 

stems and horn corals, Amplexus saphrentiformis, 

and Lophophyllum sp.? (station 6854) ________ _,_ 

49. Black papery shales _________ ___ __ ____________ _ 

48. White pebbly grit, highly cross-bedded ____ ______ _ 

47. Reddish-brown sandstone ______ ___ - - -----------

46. Dark-gray quartzite ________ ___________ _ ---- ---

45. Gray sandstone marked with ripples about 3 inches across _________ _______ _____ ________________ _ 

44. Red sandy shale, slightly micaceous ____________ _ 

43. Coarse grit, almost white ____ _______ ___________ _ 

42. Light-gray conglomerate ______________ --_------

41. Gray coarse pebbly grit _______ ________________ _ 

40. Largely covered. All outcrops and talus of lightgray to white pebbly grit. Som~ brown and gray quartzite ___________________________________ _ 

39. Sandy limestone, almost black; becomes rich brown 

onweathering-- ------------------~---------

38. White sugary sandstone; shows well-developed crossbedding __ _____________________________ _ 

37. Covered; appears to consist largely of light-gray 

grit ___________ ____ ---.c-------'""-------- ----

36. Dark-gray limeston.e; weathers brownish; contains 

coarse grains of white quartz. No fossili observed_ 

35. Light grayish-brown sandstone ___ ---- __ -- ___ . ___ _ 

34. Dark-gray quartzite_----- __ ------------------_ 

33. Light-gray grit, rather pebbly; pebbles in streaks, cross-bedded _______________________________ _ 

32. Black grit, soft; contains numerous fragments of 

black shale and carbonaceous matter ________ _ 

31. White to light-gray pebbly grit; contains abundant 

small quartz pebbles. Pronounced cross-bedding_ 

30. Dark-gray limestone; weathers brownish gray. 

Thin-bedded. No fossils observed ____________ _ 

29. Shales, covered _____ ----------------------- ___ _ 28. Coarse gray grit _____________________ _________ _ 

27. GrayLh-brown shaly sandstone, partly covered __ 

26. White cross-bedded coarse sandstone ____________ _ 

25. Dark-gray limestone; weathers brownish, granular 

appearance, no fo~:~sils visible _________________ _ 

24. Black sandy shale, slightly micaceous ___________ _ 23. Covered ______ ____________________________ ___ _ 

22. Coarse gray sandstone _____________ ___________ _ 

21. Covered, probably sandstone ________ _____ ____ _ _ 20. Porphyry _____ ________________ ___ _______ _____ _ 

19. Dark-gray sandy shale ___ ____ ________ ___ __ __ _ _ 

18. Gray sandstone, slightly pebbly..., _______________ _ 

17. Covered ___ _______________________________ ___ _ 

Feet 

2. 6 

2. 4 

3. 5 

2. 1 

1.5 

11. 0 

3. 6 

1.8 

2. 0 

13. 1 

44.4 

4. 1 

2.4 

5 

7. 2 

52. 2 

11. 8 . 

6. 1 

8. 0 

2. 4 

18. 1 

3. 2 

14. 1 

212.0 

4. 6 

27.0 

41. 0 

3. 6 

20.0 

8. 0 

25.0 

6.0 

31. 5 

23.0 

3. 1 

6. 0 

6. 1 

24. 5 

4.3 

1.4 

14.3 

25.5 

9. 5 

66 

6 

17 

12. 5 

Section of part of Weber (?)formation at west end of Pennsylvania 

Mountain-Continued 

Feet 

16. White coarse quartzitic grit, · somewhat pebbly at 

top_________________________________________ 12. 5 

15. Dark-gray limestone; weathers brownish_________ 2. 4 

14. Gray sandy shale______________________________ 12. 0 

13, 12. Coarse gray gritty sandstone__ ________________ 25. 2 

11. Dark-gray sandy shale_________________________ 4. 6 

10. Gray quartzitic sandstone _____________________ ~ 6. 3 

9. Light-gray granular sandstone ________ ____ ----__ 15. 6 

8. White quartzite, fine-grained, very hard__________ 17. 2 

7. Covered, probably sandy shale_________________ 4. 6 

6. Calcareous sandy shale, greenish gray when fresh; 

weathers light yellowish brown ___ - ______ ----_- 5. 5 

5. Black shale. Bed differs in thickness from place to 

place. Contains abundant impressions of land 

plants, identified by C. B. Read as Stigmaria 

verrucosa, Neuropteris dluhoschi, Sphenopteri~ 

asplenioides, Cordaites sp. (locality 8050)---- _ _ 2. 8 

4. Light-gray quartzite, rather thin-bedded_________ 15. 5 

3. Black sandy shale, slightly micaceous; contains poor 

plant fragments and impressions of stems ___ -___ 1. 1 

2. Light-gray quartzite, fine-grained, hard _____ - . --- 7. 5 

1. Quartzite, originally probably gray; now highly 

silicified and light gray to white. Hard ___ ---__ 6. 5 

Porphyry; ·large, thick, almost domelike intrusion. 

A study of the outcrops at the base of Evans Peak, 

west of Pennsylvania Mountain, suggests that there is 

about 6'5 feet of Weber (?) beds below the porphyry. 

Section of part of Weber (?)formation along south side of Empire 

Hill 

[Taken from east to west. Section commences at top of porphyry marking the 

second (western) fault mapped by Behre. Includes only about the lower third of 

the formation] 

Section crosses axis of a syncline and a repetition of 

beds commences. 

Feet 

60. Black shale; contains a few poor impressions of plants _______________________________ .--_--__ 54· 

59. Fine-grained gray sandstone_____________________ 28. 6 

58. Dark-gray to black slabby micaceous sandstone; 

contains a few beds of arkosic grit_ _ _ _ _ _ _ _ _ _ _ _ 61. 3 

57. Greenish-gray fine-grained micaceous · sandstone, 

slightly arkosic______________________________ 5. 0 

56. Light-gray arkosj.c sandstone_____________________ 11. 5 

55. Light-gray sandstone with a few thin interbedded 

54. 

53. 

52. 

51. 

50. 

49. 

48. 

47. 

46. 

45. 

44. 

43. 

42. 

layers of dark-gray shale. Sandstone slightly 

arkosic; shale micaceous______________________ 20. 1 

Black papery shale---------------- - .., ----------- 18. 0 

Gray sandstone, thin-bedded, slightly micaceous. 

Surfaces marked with 2-inch ripples____________ 4. 7 

Dark-gray sandy, slightly micaceous shale________ 6. 5 

Black papery shale_____________________________ 4. 7 

Dark-gray shaly sandstone______________________ 5. 0 

Dark-gray arkosic grit__________________________ 6. 0 

Dark-gray shalysandstone, very micaceous________ 20. 0 

Light-gray arkosic sandstone; contains a few pebbles 

1 ~ inches or less in diameter_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 13. 7 

Dark-gray sandstone alternating with black micaceous sandy shale____________________________ 14. 0 

Dark-gray shale (J-48-S)-------------- ---------- 1. 8 

Gray arkosic sandstone, rather fine grained________ 14. 8 

Dark-gray sandy ·micaceous shale_________________ 5. 1 

Gray arkosic sandstone with a few pebbly and gritty streaks ________________ • ~ ~, _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . 52. 6 
PALEOZOIC FORMATIONS OF THE MOSQUITO RANGE, COLORADO 41 

Section of part of Weber (?)formation along south side of Empire 

Hill-Continued 

41. 

40. 

39. 

38. 

37. 

36. 

35. 

34. 

33. 

32. 

31. 

30. 

29. 

28. 

27. 

26. 

25. 

24. 

23. 

22. 

21. 

20. 

19. 

18. 

17. 

16. 

15. 

14. 

13. 

12. 

Feet 

Dark-gray fine-grained micaceous arkose; weathers 

rusty brown_______ __________________________ 2. 3 

Light-gray arkosic grit__________________________ 10. 0 

Dark-gray micaceous shale that becomes black at 

toP----------------------------------------- 15. 2 

Light-gray arkosic sandstone_____________________ 7. 0 

Black micaceous shale. A few streaks appear to be 

slightly calcareous ___ ------------------------ 5. 11 

Alternating sandstone and sandy micaceous shale. 

Sandstone light gray; shale darker------------- 49. 0

1 

Dark-gray, slightly micaceous sandstone, hard_____ 2. 5 

Dark-gray shaly micaceous sandstone_____________ 6. 5 

Light-gray arkosic sandstone; weathers rusty brown; 

contains mica flakes as much as three-eighths of an inch across ______________________________ _ 

Dark-gray sandy shale with interbedded sandstone_ 

Dark-gray sandstone __ :_ _________ -~ _____________ _ 

2. 7 

12. 5 

3. 0 

Dark-gray sandy shale, micaceous _______________ _ 

Gray arkosic grit; contains a little mica. Poorly 

bedded, easily eroded. Contains some fragments 

&31 

of shale (J-47-S>---------------------------- 10.2 

Dark-gray sandy shale and soft . sandstone; contains 

abundant fine white mica_--------- __________ _ 

Coarse light-gray sandstone __________ ------------

Impure shaly limestone _____________ --------- __ _ 

Black sandy shale and soft sandstone, micaceous ___ _ 

13.0 

7. 1 

2.0 

4.8 

Gray sandstone, rather fine grained; surfaces show coarse ripple marks ________________ _____ -----

Dark-gray micaceous sandy shale; fine mica flakes 

4. 11 

abundant __________________________________ _ • 4 

Black slaty shale with thin streaks of limestone interbedded. (Limestone averages 1~ inches thick)__ 21. 8 

Coarse gray grit________________________________ 3. 0 

Dark-gray sandy micaceous shale, with a few thin 

layers of sandy limestone and sandstone interbedded. The limestone contains fragments of shale, 

large plates of mica, and angular pieces of quartz and feldspar (J-46) _________________________ _ 

Dark-gray sandstone ___________________________ _ 

I 7. 51 

1.9 

Gray sandy shale ____________________________ .:. __ 

Dark-gray sandstone, almost black ______________ _ 

Gray sandy shale, slightly micaceous _____________ _ 

Dark-gray sandstone ________________ ------ _____ _ 

Black shale with numerous thin beds of dark-gray 

limestone. Abundant Marginiferas in a few layers near center. Fossils include crinoid stems. 

Lophophyllum profundum, Cleiothyridi a pecosi'l, 

Composita subtilita, Chonetes geinitziq,nus'l, Marginifera ingrata, Productus cora, Prod,uctus cora 

2. 5 

3. 5 

17.5 

2. 1 

var. nodosus, Productus aff. P. perted,.uis, Pustula 

n. sp., Strophalosia spondyliformis, E~p~emus carbonarius (lcrcality 6855a)---------------------- 65. 31 

Black papery shale_ _-------~___________________ 3. 8 

Alternating limestone and shale. Limestone dark 

gray; weathers light gray. Contaibs particles of 

shale. Some layers at top are fossiliferous and 

yielded crinoid stems, Archaeocidaris-sp.?, Fistulipora sp.?, Orbiculoidea sp.? (2 species), Chonetes 

aff. C. geinitzianus, Composita su~tilita, Derbya 

crassa'l, Productus cora, Productus cdra v~r. nodosus, Productus coloradoensis, Productus n. sp. aff. 

P. semistriatus, Pustula nebraskensis var., Deltopecten aff. D. scalaris, Enchostoma sp.?, PhiUipsia sp.? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ __ _ _ _ _ __ _ 102. 1

1 

I 

Section of part of Weber (?) formation along south side of Empire 

Hill-Continued 

11. Gray calcareous sandstone; weathers brown; thinbedded; contains a few fine mica flakes; at top (10) 

Feet 

is about 2 feet of material which suggests altered 

gypsum (J-40)------------------------------ 10.2 

9. Dark-gray limestone with some interbedded limy 

shale; ·weathers light; contains some suggestions 

of fossils but nothing recognizable______________ 56.5 

8. Larg~ly covered. Part if not all ia black papery 

shal~----- -- -------------------------------- 11.0 

7. Dark-gray limestone; weathers light; contains small 

crinoid stems and small fragments of shells______ 12. 5 

6. Arkosic grit____________________________________ 10.0 

5. Gray sandstone and grit; 'weathers yellowish_______ 17. 2 

4. Dark-gray shale and, thin shaly limestone, the limestone weathers light gray ____________ --- __ ---- 10. 1 

3. Dark-gray limestone; weathers light gray. Weathered surfaces show some small quartz particles 

and what appear to be numerous small pieces of 

black shale ________________________ - _- __ ---- - 1. 3 

2. Black papery shale_____________________________ 12.2 

1. Altered and shattered impure limestone, stained yellow to brown _______________ ___________ - _ ---- 10 

Fault. 

Porphyry. 

Section of part of Weber ('I) formation in Board of Trade Cirque 

[About 2 miles east of Leadville, Colo. This section was measured for Mr. Behre's 

report on the Mosquito Range region. It does not show either the top or bottom 

of the formation but covers the largest and best outcrop of the Weber (?) in the 

vicinity of Leadville. According to Behre, this section starts over halfway up in 

the Weber(?). He thinks it represents material in the upper third of the forma· 

tion but below the top. It begins roughly N. 30° E. from the Ibex mine and S. 30° 

W. from Dyer Peak] 

51. 

50. 

49. 

48. 

47. 

46. 

45. 

44. 

43. 

42. 

41. 

40. 

39. 

38. 

37. 

36. 

Base of thick sill of Lincoln porphyry; the same 

porphyry that is exposed on Little Ellen Hill. 

Light-gray grit, very slightly micaceous. Partly 

covered. Appears to contain some interbedded 

sandyshale----------------------~------~---

Black micaceous shale _______ -------------------

Largely covered; appears to be gray grit. Some is 

highly conglomeratic, with quartz pebbles as much as 4 inches across _______ _. ______________ _ 

Porphyry sill, 63.3 feet thick. 

Rather' fine grit, moderately arkosic; shows coarse 

cross-bedding---------------------------~----

Covered, heavy sod _________ --·------------------ Coarse pebbly arkosic grit __ _: __ ______________ . ____ · Covered, sod _________________________________ _ 

Dark-gray to tan shale, partly limy, partly micaceous. 

Most of it sandy and slightly micaceous. One 

layer about a foot thick, very fine grained and calcareous __________________________________ _ 

Covered, sod __________________________________ _ 

Gray ·grit; contains a few quartz pebbles, an inch or 

less across, and a few small pieces of feldspar _____ _ 

Dark-gray limy, shaly sandstone, slabby weathering_ 

Covered but appears to be gray sandy shale ______ _ 

Light-gray grit, rather fine grained butcontainsafew 

scattered quartz pebbles 1% inches in size. Some 

beds near top slightly arkosic _________________ _ 

Brownish-gray shaly sandstone, slightly micaceous. 

Beds appear to be lenticular. Thickness appears 

to be about half the intervaL ________________ _ 

Light-gray arkosic sandstone, massive-------------

Feet 

114.4 

1.5 

148.9 

12.6 

10. 1 

4.0 

22.0 

6+ 

10.5 

11.2 

2.0 

13.0 

10.3 

4.0 

8.8 
42 SHORTER CONTRIBUTIONS ·TO GENERAL . GE0LOGY, 1934-35 

Section of part of Weber(?) formation in Board af Trade Cirque~ . arbitrarily used the top of his··Jacque Mountain lime;.;, 

Continued stone for the base of his tWyoming formation and 

35. Light-gray sandy shale, slightly micaceous. Rep- Feet stated: 

resents about half the intervaL ____ . ___________ _ 

34. Dark-gray calcareous sandstone, with a few fine· mica flakes __ ~ ______________________________ _ 

33. Light-gray arkosic sandstone ____________________ _ 

32. Black limy shale ______________ .:_ _______________ _ 

3L Gray arkosic sandstone __ · _____________________ ..:_ 

30. Saridy calcareous shale,.. ______________________ .:. __ 

29~ Light-gray, slightiy arkosic sandstone that tends to 

28. 

27. 

26. 

25. 

24. 

23. 

22. 

21. 

weather · brown, slightly limy. Grades downward into coarse pebbly arkosic grit showing cross- bedding to the south ______________________ :_ __ 

Gray sandy shale, partly covered ________________ _ 

Light-gray, almost white sandstone, grading downward into arkosic grit, slightly pebbly near base. 

Poorly . cross-bedded _________________________ _ 

Dark-gray arkosic sandstone, slightly micaceous, 

particularly along bedding planes; contains a few 

streaks of quartz and feldspar pebbles 1~ inches 

in size _____________________________________ _ 

Black sandy shale, fine-grained at the top, becoming 

sandy and lighter in color toward the bottom ___ _ 

Coarse grit, dark gray when fresh _______________ _ 

Coarse gray sandy shale __ ____________________ --

Dark-gray sandstone_· ___________________ _______ _ 

Dark-gray sandy calcareous shale ______ _________ _ 

20. · Dark-gray arkosic sandstone, grading downward into 

19. 

18. 

17. 

16. 

15. 

14. 

13. 

12. 

11. 

a coarse light-gray grit, with streaks of pebbles __ _ 

Covered, probably shaly sandstone ______________ _ Coarse gray grit ________________________________ _ 

Covered, probably gray grit __ __________________ _ 

Sandstone _________ , ___________________________ _ 

Impure shaly limestone ____________ ____________ _ 

Gray grit ________________________ "'- ____ :.. ______ _ 

Dark-gray fine-grained sandstone_...: _____________ _ Gray shale ___________________________________ _ 

Impure shaly limestone with considerable white mica 

on bedding planes; weathers olive-green __ _____ _ 

10 .. Dark-gray arkosic sandstone ____________________ _ 

9. Dark-gray impure shaly limestone; weathers white __ 

8. Dark-gray to brown arkosic grit; contains some 

streaks of 2-inch pebbles of quartz and feldspar, 

the latter remarkably fresh looking ____________ _ 

7. Dark-gray calcareous sandstone, rather fine grained 

· 6. Light-gray coarse arkosic sandstone ______________ _ 

5. Black slaty shale; shows some poor impressions of 

plant stems and fibers. Some layers sandy and 

slightly micaceous ___________________________ _ 

4. Bl~ck shaly sandstone _________________________ _ 

3. Dark greenish-gray shaly limestone ______________ _ 

2. Covered; probably gritty sandstone; some beds 

slightly conglomera tic ____ ___________________ _ 

~- Gray to dark-gray alternating sandstone, grit, _ and 

shaly sandstone _____ ...: ___________ ...: ___________ _ 

Covered (end of section measured). . 

PENNSYLVANIAN-PERMIAN BOUNDARY 

7. 4 

2. 6 

. 7 

3. 8 

7. 9 

2. 0 

43. 0 

4. 6 

25. 7 

18. 7 

11. 3 

7. 0 

7. 3 

3. 0 

4. 5 

21. 6 

29. 2 

35. 4 

11.8 

8. 3 

6.0 

18. 1 

4. 2 

1.5 

8. 4 

5. 7 

5. 8 

6. 8 

5. 7 

17.4 

11. 0 

16. 5 

3+ 

35.5 

49.3 

At the present time a definite boundary cannot be 

d:rawn between the Pennsylvanian and the Permian of 

this region. Emmons 42 in the Tenmile district 

42 Emmons, 8. F., U.S.Geol. Survey Geol. Atlas, Temi:J.ile district sp!)cial folio 

(no. 48), p. 2, 1898. 

If the Permian is represented in Colorado * * * it 

would be included in these beds, which· have evidently· been 

deposited in direct and unbroken succession over the upper 

Carboniferous. 

There is . l,lO stratigraphic br~ak and no particular 

lithologic change, and sufficient paleontologic data to 

permit a distinction have not yet been obtained. In 

' general it appears to.'have been the pl,'actice of most 

geologists to. call the deposits Maroon wherever they 

consist l~rgely or ~nti~ely of red beds. This is not 

good practice·, for it can be easily demonstrated that 

the deposition of red beds did not start at the same 

time in all parts of the Mosquito Range. In· adjoining areas there is an ev,en greater differe:p.ce in the horizon at which red sediments first appear---,-in fact, a 

lateral gradation from the Weber '(?) sediments into 

red beds was observed in several localities, and beds of 

red material appear in ·the gray beds. far below the 

horizon where red sediments predominated. In .the 

Red Cliff _and Minturn areas, northwest of · the Mosquito Range, thick red beds occur below limest.one and 

shale carrying definite Pennsylvanian ·fossils, and still 

farther :r;wrthwest, around -McCoy, almost the. entire 

Pennsylvanian section has a brilliant red color . . 

Fossils .become progressively scarcer in the sequence 

of. beds upward in the . series. A careful search has 

shown, however, that the redbeds are by no means 

devoid of organic . remains. A surprising number of 

limestone beds are sandwiched between the sandstones 

and grits. Many of thes~ -beds carry maririe fossils. 

Land plants have · b~en ·found in ,Several localities. 

Future work in the areas west and northwest of the 

Mosquito Range will probablY. supply sufficient material to permit a definite determination of age and will 

permit the recognition and correlation of zones within 

the red beds. It Will probably .also supply a basis on 

which a definite boundary may ·be drawn within the 

actual area of the Mosquito Range. 

EmmQns -- sta~~d · that. his Maroon of .. the · Tenmile 

district carried ~ tCoal .Measures fauua, and though it 

is now kno.wll,. that th~ P~nnsylv&n}an does .nQt run as 

high . as his .;: ~acque Mountain limestqp.e, .there is no 

doubt -that ~t 1e~st a considerable ·portion of the -lower 

red be9-~r :are of Pennsylvanian age.'· · ' . 

Aburidarit fo~s~ have oeen fOlU1<(in the lower part 

of the Weber. (?Yfo.rmation, all of w}uch giv!3 it ·a definite lower ·Pennsylvanian age. Fossils obtained in the 

Jacque Mountain limestone and adjoining ,beds are of 

a definite Permian type. David White obtained 

Permian plants at.' a much "lower ~tratig:btphic level 

near Red · CUff and in the vic~ty ~f Minturn. However, the sediments· .. appear. to, form an unbroken sue- • ! • 
PALEOZOIC FORMATIONS OF THE MOSQUITO RANGE, COLORADO 43 

cession between the beds that carry the Pottsville fossils and those, thousands of feet higher, that carry 

Permian forms, so it seems only reasonable to suppose 

that some of the sediments must represent middle and 

upper Pennsylvanian time. 

During the summer of 1931 the writer spent some 

time studying the red beds west of the Gore Range. In 

that region there is a maximum of about 5,700 feet of 

sediments between: the Jacque Mountain limestone 

and the horizon of the Leadville limestone. The 

paleontologic material obtained suggests that about 

the lower 2,000 feet is of Pennsylvanian age, whereas 

the beds above are Permian. It seems probable that 

in the Leadville and Alma districts the same would be 

approximately true. 

MAROON FORMATION (PENNSYLVANIAN? AND PERMIAN) 

The sediments typical of the Weber (?) formation of 

this area pass upward · and in several places laterally 

into a series of red beds, mainly sandstone and sandy 

shale but locally containing lenticular conglomerate 

and limestone . . These deposits in the Breckenridge 

and Tenmile districts have been called the Maroon 

formation. 

At first glance the sediments appear to be all red and 

to consist mainly of coarse clastic deposits. Closer 

inspection, however, reveals a surprising amount of 

limestone and many gray, greenish-gray, and brown 

beds. 

0 

Erosion has removed the Maroon from the upper 

portions of the Mosquito Range, especially in the 

Leadville and Alma -districts. The Maroon is, · however, well developed along the eastern slopes of the 

range and in South Park, where it covers large areas. 

It is also present over considerable areas to the northeast in the Breckenridge district and to the northwest 

in the Red Cliff and Gilman districts. To the north, 

in the Kokomo and Robinson districts, it attains a 

great thickness and covers large areas. 

In South Park the sediments are mainly rather fine 

grained sandstone and sandy shale, locally with thin 

beds of limestone, mainly of algal origin. In a few 

places streaks or thin beds of gypsum have developed. 

Ripple marks and sun cracks are not uncon1mon on the 

surface of the beds. 

The deposits tend to be coarser in character in the 

other districts mentioned, containing a larger proportion of conglomerate, grit, and sandstone. Some 

shale occurs and limestone is common, some of the 

beds being rather thick. 

At least the greater part of the Maroon is of Permian 

age.