ALGAE REEFS AND OOLITES OF THE GREEN RIVER FORMATION. 

By W. H. BRADLEY 

INTRODUCTION 

Reefs .or beds and is.olated n.odules .of fresh-water 

algal limestone are abundant in several parts .of the 

Green River f.onnati.on .of Wy.oming, C.ol.orad.o, and 

Utah. L.ocally they c.onstitute nI.ore than 8 per cent 

.of the basal InClnber .of the f.ormati.on and .occur in 

single reefs .or gr.oups .of reefs as much as 5.5 meters 

(18 feet) thiclc (See pi. 29, A.) O.olitic liInest.one and 

algal pebble beds are als.o plentiful but thinner. 

These algae reefs and .o.olitic beds are interesting n.ot 

.only because they nIake up an appreciable part .of the 

f.onnati.on but als.o because they indicate that the parts 

.of the lakes in which they and the ass.ociated beds 

were f.ornIed were shall.ow and clear except in times .of 

stonn, that the lakes had sheltered bays in which an 

emergent vegetati.on fi.ourished, and that the streams 

:feeding the lakes br.ought in a c.opi.ous supply .of diss.olved calcium salts. 

It is also w.orthy .of passing n.ote that the algae reefs 

.of the Green River f.onnati.on, alth.ough f.ormed in 

inland lakes during the nuddle part .of the E.ocene 

ep.oeh, are rOInarkably similar t.o th.ose f.ound in the 

11i.oeene lake beds .of the Rhine Valley in Germany. 

The SaIne species .of alga has been the chief agent in 

f.orming the reefs in each .of these tw.o widely separated 

l.ocalities, and, s.o far as the writer is aware, dep.osits 

with a c.omparable internal structure are elsewhere 

unkn.own. 

STRATIGRAPHY AND ECOLOGY 

The algae reefs .of the Green River f.ormati.on aTe 

In.ost plentiful in sh.ore phases .of the f.ormati.on, as 

between White and Yampa Rivers in M.offat and Ri.o 

Blanc.o C.ounties, C.ol.o., and in the n.ortheastward 

extensi.on .of the Bridger Basin in Sweetwater C.ounty, 

'¥y.o. In b.oth these areas the f.ormati.on c.onsists .of 

silty shale, sandst.one, .ostrac.ode and .o.olitic limest.one, 

and shell lnarl. Oil shale is practically absent, and 

beds .of shale c.ontaining even a small quantity .of 

.organic lnatter are n.ot abundant. In these areas 

bedlike algae reefs are irregularly distributed thr.ough 

the entire thickness .of the f.ol'lnati.on, bt'lt elsewhere in 

the Green River f.ormati.on algae reefs are c.onfined 

a1rn.ost wh.olly t.o the basal member, wh.ose lith.ol.ogy 

is similar t.o that .of the sh.ore phases. The left-hand 

c.olumn .of the secti.on sh.own in Plate 28 illustrates 

100874°-2!)--14 

the kinds .of r.ocks with which algae reefs are habitually 

ass.ociated. This lith.ol.ogy, m.oreover, is fairly typical 

.of the basal member .of the Green River f.ormati.on in 

Wy.oming as well as in C.ol.orad.o and Utah, alth.ough 

the pr.oP.orti.ons .of the different kinds .of r.ock vary 

c.onsiderably fr.om place t.o plaee . 

S.o far as the writer has .observed algae reefs are 

n.owhere cl.osely associated with beds .of even m.oderately rich .oil shale but .only with sandy and liIny 

shale beds wh.ose .oil yields range fr.om a trace to ab.out 

5 gall.ons a ton. This is n.ot surprising, h.owever, 

because the c.onditi.ons .on the lake b.ott.om where beds 

.of richer .oil shale f.ormed were utterly different fr.om 

th.ose where algH,e reefs f.ormed. The f.ormati.on .of 

rich .oil shale requires stagnati.on .of water and active 

putrefacti.on .of vast quantities .of .organic lnatter, the 

pr.oducts .of which w.ould quickly precipitate the lime 

in s.oluti.on and also f.oul the b.ott.om s.o that it w.ould 

be unfav.orable f.or m.ost benth.onic plants except sapr.ophytes. These c.onditi.ons are clearly inilnical to the 

f.ormati.on .of algae reefs and explain their absence fr.om 

the .oil-shale z.ones and als.o fr.om much .of the remainder 

.of the Green River f.ormati.on, which c.onsists predOl~:­

inantly .of shale that nIay be c.onveniently termed l.owgrade .oil shale, defined as s.omewhat limy shale that is 

finely laminated and that contains en.ough .organic 

matter t.o yield .on distillati.on less than 15 gall.ons .of 

.oil t.o the sh.ort t.on. In m.ost places beds .of richer .oil 

shale are interbedded at rather wide intervals with the 

l.ow-grade .oil shale. The middle and right-hand c.olumns .of Plate 28 sh.ow the typicallith.ol.ogy .of the Green 

River f.ormation ab.ove the basal member. 

Locally, as in the vicinity .of Parachute Creek, 

C.ol.o., that part .of the secti.on between the basal 

member and the l.owest .oil-shale z.one c.onsists .of hard 

limy .or silty shale and c.ontains a few thin algae 

reefs. In a few places that part .of the f.ormation 

ab.ove the upperm.ost .oil-shale z.one also oontains 

thin algae reefs, as in the vicinity .of Indian Cany.on 

and near the Duchesne-Uinta county line in Utah. 

(See pi. 31.) .. 

Each.of the tw.o great E.ocene lakes, .one in Wy.oming 

and the .other in C.ol.orad.o and Utah, in which the 

basal member .of the Green River f.ormati.on accu-. 

mulated may be pictured as a very br.oad sheet .of 

water fl.o.oding a large, nearly level fluviatile plain, the 

203 
204 SHORTER CONTRIBUTIONS TO GENEHAL GEOLOGY, 1928 

I 

top of the Wasatch formation. This plain was built 

up of clay, silt, and sand brought down by streams 

from the surrounding nlountains, and as the alluvial 

material is predOlninantly clay the basinward slopes 

must have been very gentle. 

The beds of clay and stream-channel sandstone of 

the Wasatch formation in the greater part of each 

basin are comparable to the youngest flood-plain 

deposits in Sacramento Valley, Calif., between Butte 

City and Montezuma Hills, which, according to Bryan 1 

consist chiefly of blue clay and silt with deposits of 

coarser sand and gravel that were laid down in more 

or less braided stream channels. The gradient of 

Sacramento River through this area is a little less than 

19 centimeters to' the kilometer (1 foot to the mile). 

If this gradient is assumed for the basin floors over 

which the earliest Green River lakes spread and if it is 

also assumed that the water was not more than 3 or 4 

meters (10 or 15 feet) deep near the shores where the 

algae reefs formed, then the deepest parts of the lakes 

near the centers of the basins may have been as much 

as 15 or 18 meters (50 or 60 feet) deep. But other 

things being equal, lacustrine sedimentation must soon 

have lessened this relief on the lake floor so that while 

the greater part of the basal member was being formed 

the lake bottoms were nearly level. On the other 

hand, the earliest 'lakes may have started as small 

ponds and backwaters along the stream courses in the 

alluvial plain and expanded very gradually, filling their 

basins and leveling up the plain as they grew, until 

finally they spread over the entire plain from mountain 

flank to mountain flank . 

. In these two great shallow lakes algae flourished 

and built bedlike reefs that expanded broadly over the 

smooth lake floors. Fish, mollusks, crustaceans, and 

aquatic insect larvae were also plentiful in the lakes, 

and turtles (Baptemys sp. and Echmetemys sp.), crocodiles, birds, and small camels, as well as myriads of 

winged insects, frequented the lake shores. Along some 

shores there were marginal swamps which persisted 

for a considerable time and whose former positions are 

revealed now by thin coal beds. 

But these lakes, despite their enormous area and 

slight depth, must have been fairly stable water bodies, 

for some of the thicker algae reefs required, according 

to the writer's estimate, at least 355 years to form. 

Dyring that time only slight changes in water level, 

rate and manner of circulation, and rate of sroimentation could have occurred. Such changes would register in the growth layers of the reef. A considerably 

longer period of static equilibrium is indicated by the 

composite reef near the divide between Douglas and 

Salt Creeks, Colo., which is 5.5 meters (18 feet) 

thiclc 

1 Bryan, Kirk, Geology and ground-water resources of Sacramento Valley, Calif.: 

U. S. Geol. Survey Water-Supply Paper 495, PP. 7, 10, 39-43, 1923. .. ~ 

The periodic stability indicated by the algae reefs 

suggests that the lakes had outlets during at least part 

of the time, for lakes in inclosed basins are extremely 

sensitive to climatic changes, and their levels fluctuate 

perceptibly even" when ordinary weather observations, 

taken at a limited number of localities in their neighborhood, fail to indicate analogous changes in atmospheric conditions." 2 It is possible that between such 

periods of stability in the early stages of the Green 

River lakes they did not overflow. The prevalence of 

sun-cracked bedding planes and mud curls in some 

parts of the basal member supports this hypothesis. 

Yet complete desiccation was probably not frequent, 

if indeed such an extreme condition was even approached. In the basal member no salt crystallized 

out in the bottom mud. These lakes, however, may 

have been comparable in relative permanence, depth, 

and content of dissolved salts to Goose Lake, Oreg. 

Goose Lake lies in a region whose average annual rainfall is about 51 centimeters (20 inches). It contains 

about 1,000 parts per million of dissolved salts, rarely 

overflows, and although very 'shallow has never been 

known to dry Up.3 

It is plain that in later stages of the Green River 

lakes they had no outlets, for they became progre~­

sively more saline until finally large quantities of 

glauberite crystallized out in the bottom mud. During 

the saline stages many of the principal oil-shale beds 

formed. The deposits of these later stages are clearly 

different from those of the basal member and reflect 

marked changes in the aspect and constitution of the 

lakes as they grew older. 

FIELD WORK AND ACKNOWLEDGMENTS 

This paper describes a collection of algae reefs and 

oolites made during the field seasons of 1923, 1924, 

and 1925. During 1923 the writer was assisted by 

C. H. Dane, of the United States Geological Survey; 

in 1924 by C. E. Erdmann, also of the Geological 

Survey; and in 1925 by R. D. Ohrenschall. These 

men the writer wishes to thank for their cooperation 

in the field and their interest in the problems that have 

. since arisen. 

In the autumn of 1925 the writer visited Canandaigua Lake, N. Y., to collect recent algal pebbles, 

and in July, 1926, he visited Green Lake, N. Y., to 

examine and collect specimens of the algae reefs now 

forming there. 

MODERN ALGAE REEFS IN GREEN LAKE, N. Y. 

STRUCTURE 

An examination of the structure of algae reefs now 

forming in Green Lake, N. Y., assists greatly to in2 Russell. I. C., Lakes of North America, p. 71, 1895. 


8 Waring, G. A., Geology and water resources of a portion of south-central Oregon: 


U. S. Geol. Survey Water-Supply Paper 220, PP. 12,38, 1908. 
U. H. GI!IOLOtHCAL SU nVEY 

C 

oil-shele zone ~ Top' of principal '_11111.1­

Mahogany zone; average yield about 40 g"lIs. 

Shl!Jly limestone;

insects and leaves 

sh~/e -IS gal/s.-salt molds 

Limy shale;sun cracks 

and salt molds 

gray limy shele 

-Oil shl!Jle -15-20 9alls. 

shale; insects end leeves B Top of b!!sa I 


member 
 Barren limy shflle 

shale - 10galls. 

Limy shale 

shale -15galls.. 

Fino-grained Sandy paper shale burr 

sendstons,current

ripple bedded throughout '111;il~Brown and grey h'my shale ~ Oil shale -25gal/s.-s8It molds 

Papery I;my shale; 

selt-molds 

Oil sh81e -20galls. 

Break of unknown Barren limy sh8le, amount, probably limestone,and thin 

oil-shale beds not lerge ~~ii~iilll Base of principal 


oil-shele zone Oil shale -15-20 galls.. 

Brown finely lamineted she/~ 

Soft brown shale with adult 

insects and plant fragments 

-Sandy shale 

Top CYf lower } Limy shale 

oif.shale zone '~!!I~~--Oil shale -ISgalls.

~ } Limy shole 

1~~~~~ij 0;1 shale -/2-15 9alls. ~ Limyshole of' oolitic withthi" beos limestone 

Chocolat(rbrown limy shale 

Fine -gr8ineo' burrs8ndstone 

part rpassive,part cross-bedded 

shale - 10-12 ge//s 

Brown limy' shale'and 

thin all-shale lenses 

Herd limy and silty shBle Oil shale -35g81Is. 

Lamin'8ted 

brown limy 

chocolateshale 

Algae reef's end 


oolitic limestone 


Shaly sandstone with mud . curls and rishbones Barr(?n lifo/. Shale and 

several beds of'oil shelg 1~;~=~~t~/9ae reef'and oolitic limestone 15 -20 ~alls. 

greenisH-gray sQl!Jle sh81e -15gallS. 

Hard light-brown limy shale 

L/~ht-brown low-grade Medium to fine grained send­oil shala with thin 20-gall. stone. in part msssive,in pert o/~-shale beds 

cross-bedded;contl!Jins shale 

conglomerate 0/1 she/e -20 g811s. 

Bese of lower h!. 5 II. oil-shale zone iiiliiiil{":S;OTtvmYShak s a e - / g8 s. Dense ~reenish-9roy

pyritlrerous slial" 

with sandy lenses i Herd chocolete-brown

lamineteo' shale with thin 

oil-shale streaks 

. - - 01/ shale - 25 gI:J/ls. 

laminated chocolate-brown 

shale and tflln oolitic limestone 1==========1} 

Finely 

brown 

laminated 

shale with light­mud 

cvrls al?d sun cracks 

ihin-bedd;,dsl!Jn& shele end 

thin sandstone beds. 8eds contcun 

and fi"hbon/1s mlJd c(lr/s, end mud ere sun­lumps, 

iillllt.~:Laminated shale -10limy gallS. shele 

crecked andripplB bedded 

Sandy ostracode limestone 

Fine-gr"ined cross-bedded 

shele 

iiiiiili",L~I;m;~;s~h;~;/~e; 

cracked 

ripple-bedded sandstone 

f'i,,!>bones rishbones rippled

and sun­Larvae beds reef's, oolitic limestone, 

finely 18min8ted limy shale 

R8ther sort IIjht-brown limy and finely lammeted shale;rew beds sun cracked (jnd oscilletion rippled 

iI.~'tGreeniSh-grey cley Oil shale - 10galls. 

Hard light-brown lI:Jminated shale 

ostracode limestone Variegated red and 


gray sandy cl8Y 


;;111;11 Sort· papery ostr"code Oolitic limestone shale with plI:Jnt fregmel1ts 

l

Ilt:siltstone 

Sort p"per shale 

limestone 


Variegated clay or 
 B Wesetch {'ormetion 

A 

PROFESSIONAL PAPER 154 PLATE 28 

Rather soft chippy (md limy shale 

Limy shale with thin bed$ 

ofoil Shale and sandstone 

Hard limy shale 

shale 

shale 

~iili=r:~ shale -30-35gell$. f. Thin-hedded silty shale 

without rly larvae 

Very thin bedded silty shale contaimnq vast numbers of'rly Tarv8a. 

Thin beds 01'oil shale 

H"rdlight-hrown limy shale, platy or finely laminated, 

with sever,,1 thin' beds aT 

oil shale -10-20 gall~_ 

Low-grade oil shale 

c 


COMPOSITE SECTION OF THE GREEN RIVER FORMATION SHOWING THE DISTRIBUTION OF THE ALGAE REEFS AND THE CONTRAST IN UTHOLOGY BETWEEN 


THE BASAL MEMBER AND THE REST OF THE FORMATION 


Tho basnl mombor, up to tho breuk nenr its top, wos moasured along the Fruita-Rangely road on the divide between Douglas and Eost Salt Creeks, Colo. The remainder of the section was mPAlsurOO near tho head or Cnthedrnl Creek, approximately in soo. 6, T. 3 S., R. 99 W., Colo. The yields or the oil ... hale beds are estimated. Scale, linch = 50 feet. 
U. S. GEOLOGICAL SURVEY 	 PROFESSIONAL PAPER 154 PLATE 29 

A. 	GROUP OF SUPERIMPOSED ALGAE HEEFS IN THE UPPER PART OF 

THE BASAL MEMBER OF THE GREEN RIVEH FORMATION NEAH 

THE DIVIDE BETWEE WEST DOUGLAS AND EAST SALT CREEKS, 

COLO. 

The man's feet are at the base of the lowest reef which truncates the shaly sandstone beds below ; his shoulders arc lnvel w ith a thin reef that has unusual pencillated structure. The thin dark-<:olorcd bed at the to!, of the unit consists of algal peb­ bles some of which are shown in P late 46, B. The group is about 5.5 meters (18 feet) thick 

The upper rough part is gr~yish green ,.owing to the dense felt of algae. whose Lips were only thinly incrusted with Lime. The lower, smoother part, WhICh was buned in a soft limy mud, is yellowish gray. dense, and without living algae. Natural size 
U. S. GEOLOGTCAl, SUHVEY PROFESSIONAL PAPER 154 PLATE 30 

A. THIN SECTIO OF A RECENT ALGAE REEF FROM GREEN LAKE, N. Y. 

Showing th e tubula r molds of the thalli of a filamentous alga, Microcolf'US paludosa (KiHzing) Gommont, 

in a matrix of microerysLalline ca lcite. The darkest molds contain bakelit.e with which the specimen was impregnated for sectioning. Enlarged 75 diameters 

B. THIN SECTION OF A RECENT ALGAE REEF FROM GREEN LAKE, N. Y. 

Showing the typical spongy stru cture of the microcrystalline calcite producod by a felt of fresh-water algae. This also shows a portion of the recrystallizod and more deuse surface layer in the upper left quadrant. EuJargod 30 diameters 
u. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 31 

IIi' 109' 

4:f 

EXPLA NATION 

D 

Green River formation 

4£ 

Areas con

~ taining·algae reefs in the basal mem­ ber of the formation 

Areas ~ containing algae reefs above the basal 

member of the for­ m ation 

4f 42 

E 

IB:S::EHmJ=:::i10~::23:0==30E:=340c=:::::is:'========:=:::::J'OO MILES 

GEOLOGIC MAP SHOWING T HE DISTRIBUTION OF THE ALGAE REEFS I THE GREEN RIVER FORMATION 

Geology compiled from published reports of Winchester, Schullz, Vcatc~~:;'fr BaU, and Bradley and unpublished field data of E. E. Smith and E . G. 
A\.GAE REEFS AND OOLITES OF THE GREEN RIVER FORMATION 205 

terpret the spongy structure of 111any fossil reefs. In 

Green Lah::e algae forn1 not only fringing reefs but also 

thick incrustations on the trunks and branches of 

trees that have fallen into the water. All these deposits are exceedingly porous or spongy and consist 

of '111ore or less closely intergrown arborescent masses 

that are richly nodose. They resen1ble arborescent 

native copper but are 1110re profusely branched. (See 

pI. 29, B.) An outer layer ranging in thickness from 

about 0.25 to 3.0 centi111eters is soft and crumbly, 

but below that the deposit is as hard as ordinary 

porous limestone. 

Apparently the £01'111 of the lil11Y deposit is deternlined by the growth habit of the algae, for if the calcium carbonate in the softer outer layer is dissolved 

in dilute acetic acid there reInains a very dense felt of 

algae which retains the original dimensions and intricate fOrIn. Close to the surface the calcium carbonate, 

in the form of minute granules 3 to 6 microns in dian1eter, partly fills the interstices between the algae 

filalnents and unicells and thus makes a very imperfect 

cast of the interstices or, stated differently, a mold of 

the plants. But beeause the algae are so densely 

entangled the resulting Inolds are those of groups or 

S111all felts of the plants rather than of individual plants. 

Only rarely in such cOl11plex assemblages of algae are 

the individual filmnents or unicells so widely separated 

that recognizable molds of them are formed. (See 

pl. 30, A.) 

A little below the surface of these deposits the calcimn carbonate is somewhat coarser grained. The 

crystal growth thus indicated diminishes a little the 

spaces originally occupied by algae and also distorts 

whatever mold's of individual plants may have formed. 

This dinlinution of pore space, however, is slight, and 

the resulting deposit after the algae have decayed and 

completely disappeared is exceedingly porous and 

exhibits the typical spongy structure. Some of it 

shows clearly the dominant radial lineaments of the 

algae. (See pI. 30, B.) Although this spongy deposit· 

shows neither cell structure nor any molds of algae, it 

is highly distinctive and owing to its unusual external 

for.m is not readily confused with limestone of any 

other kind. 

The spongy structure of these recent algae reefs is 

practically identical with that found in many of the 

fossil reefs from the Green River formation. (See pl. 

34, A.) However, few fossil deposits are so porous, 

because some or even all the interstices have subsequently been filled with calcite or silica. These secondary fillings are, nevertheless, clearly distinguishable 

£r0111 the original deposit. 

Those parts of the algal deposits in Green Lake, 

N. Y., which have been buried in afinely granular gray 

or white limy silt have been son1ewhat modified. The 

intricately arborescent and finely nodose or granular 

protuberances have become smoother, more rounded, 

and more compact. (See pI. 29, B.) Thin sections 

of these parts show that the interstices have been 

filled with calcite, so that an out3r layer 0.1 to about 

1 centilneter thick is dense and somewhat banded 

concentrically. Along these bands n1any of the calcite 

crystals are radially elongated. The change is apparently inorganic and confined to those parts that are 

buried. Perhaps an1monia from the decomposing 

algae hastened the precipitation and recrystallization 

of these buried parts. 

ORGANISMS 

The dense felt of algae obtained by dissolving out 

the calcium carbonate from the material collected in 

Green Lake, N. Y., consists of an assemblage of bluegreen algae together with a few green algae. The 

most abundant forms are jficrocoleus paludosa (I{Jitzing) Gommont, Palmella miniata Leiblein, Ohroococcus helveticus Nageli, and Lyngbya subtilis W. West; 

and of these Microcoleus, by reason of its greater bulk, 

predominates, yet the minute ,cells and colonies of 

Palmella are vastly more numerous. Palmella cells 

are probably the unidentified "rounded or oval, 

very small cells" that C.' A. Davis referred to in his' 

notes on the lime deposits of Green and Round Lakes, 

N. Y., published in Walcott's description of some 

,pre-Cambrian algal deposits.4 Lyngbya and Palmella 

are most plentiful close to the surface of the algal 

felt, where they are associated with the algae listed 

below in the order of their estimated abundance: 

Hapalosiphon aureus West and West, locally plentiful. 


Gloeocapsa sp. 


Radiofilum sp. 


Rivularia sp. 


Dicothrix orsiniana (Kutzing) Bornet and Flahault. 


Diatoms belonging to several genera are scattered 

through the mass of other algae. 

The calcium carbonate precipitated by these algae 

was tested to see whether it was aragonite or caleite. 

The two most generally used chemical tests with 

cobalt nitrate and ferrous sulphate were applied but 

gave inconclusive results. Pieces tested in cobalt 

nitrate became pinkish lavender, whereas crystals 

of aragonite used as a check turned lavender but 

with a perceptibly bluer tone. Calcite crystals 

also immersed for a check remained colorless. In 

ferrous sulphate pieces of the material caused a 

yellow precipitate, which, however, had at first a 

dull greenish cast. Johnston, Merwin, and Williamson 5 have pointed out the uncertainty of these tests, 

especially if the material is finely divided or in the 

form of aggregated fine particles. 

C. S. Ross, of the Geological Survey, kindly examined some of the material for the writer and found 

4 Walcott, C. D., Pre-Cambrian Algonkian algal flora: Smithsonian Misc. ColI", 

vol. 64, p, 88, 1914. 

6 Johnston, John, :Merwin, H, E" and Williamson, E. D., The several forms of 

calcium carbonate: Am. Jour. ScL, 4th sor., vol. 41, pp. 476-478, 1916. 
206 SHORTER CONTRIBUTIONS TO GENERAL GEOI.JOGY, 1928 

that all the crystals large enough to be determined 

optically were uniaxial and therefore calcite. 

There remains the possibility that some of the finer 

grains are or were originally aragonite. That they 

are now aragonite appears unlikely, for Johnston, 

Merwin, and Williamson 6 have demonstrated that 

in aqueous solutions aragonite is unstable in the presence of finely divided calcite. These' grains are very 

small, 3 to 6 microns in diameter, and are interlocked 

with the minute calcite grains. Moreover, these 

deposits formed under water, where they remained 

for a considerable time. It also seems improbable 

that these finest grains were originally aragonite, 

for the small calcite crystals with which they are 

associated in the surface layer of the deposit are 

not idiomorphic, as they probably would be if recrystallized from aragonite. Moreover, older parts of 

the deposit obviously furnished calcite nuclei, a fact 

which in itself makes the original deposition of aragonite very improbable, as pointed out by' Johnston, 

Merwin, and Williamson. 7 

Hassack 8 and Chambers 9 have demonstrated that 

the function of algae in the precipation of calcium 

carbonate is merely to remo:ve by their photosynthesis 

the carbon dioxide from the system. Under the conditions which occur in Green Lake, N. Y., calcite is 

the stable product. Perhaps in a lake that contained 

considerable sulphate in solution aragonite containing 

some calcium sulphate in solid solution would be 

the stable form.lO 

GENERAL FORM OF THE FOSSIL ALGAE REEFS 

The algae reefs of the Green River formation have 

the form of irregular lenses or beds rather than of ridges 

or mounds, and they differ considerably in thickness 

from place to place. Little is known about their 

extent and proportions; partly because the exposures 

are inadequate but chiefly because the urgency of 

other field work has always left insufficient time to 

map them. Plate 31 shows their distribution in a general way. The shaded portions represent areas in 

which the writer has observed reefs together with a 

narrow border zone that represents their probable 

minimum extent ben~ath cover and along the strike 

of the beds from the observed outcrops. Their actual 

extent is almost certainly considerably greater than 

that shown. Those portions of the outcrops along 

White River from the vicinity of Meeker to Douglas' 

Creek, Colo., along the east side of the Bridger Basin 

in Wyoming from the Union Pacific Railroad north to 

6 Idem, p. 501. 

7 Idem, p. 483. 

8 Hassack, Carl, tiber das Verh!Utnis von Pflanzen zu Bicarbonaten iind uber 

Kalkincrustation: Untersuchungen aus dem Bot. Inst. zu Tiibingen, vol. 2, pp. 

467-473, 1888. 

Q Chambers, C. 0., The relation of algae to dissolved oxygen and carbon dioxide 

with special reference to carbonates: Missouri Bot. Garden Ann. Rept., vol. 23, 

pp. 188-204, 1912. 

10 Johnston, John, Merwin, H. E., and Williamson, E. D., op. cit., p. 482. 

the area indicated on the map by shading, from White 

River to Green River in Utah, and between Little 

Snake and Yampa Rivers, together with several localities in the adjoining country to the northwest, have 

been examined and found barren of algae reefs. The 

remainder of the unshaded portions represent either 

unexamined outcrops or areas where the formation, 

though near the surface, is not exposed. 

The shape and size of modern algal deposits appears 

to be governed largely by the lake-shore profile. The 

modern algal tufas of Pyramid Lake, Nev., like 1110St 

of the Pleistocene tufas of the ancient Lake Lahontan, 

are true fringing reefs, because the shore profiles are 

steep' and the maximum depth at which they could 

form is not far from shore. Similarly in Green Lttke, 

N. Y., the shore of which has an exceedingly steep 

profile, the algal reefs are narrow and fringing. In 

lakes with more gently sloping shores, such as Ore 

Lake, Mich.,!! the algal deposits are more bedlilm but 

thickest near shore and progressively thinner outward 

where the water deepens. Baumann 12 shows that the 

beds of algal pebbles now forming in Unter See, Gerluany, below the outlet of the Lake of Constance are 

rather thin but extend over very large areas in the 

shallow bays (1 to 4 meters deep), which are free frOlu 

strong currents. Some of those deposits are nearly 

equidimensional, but more of them are two to three 

times longer than broad. 

Apparently, therefore, algal deposits must of necessity be bedlike in shallow lakes which are free from 

strong currents and whose bottoms have a gentle slope 

and but slight relief. Over such bottoms they may expand freely, their size and shape being limited only by a 

decrease in the lime supply or changes in environment 

that would be unfavorable to the propagation of the 

algae-for example, a considerable increase in either 

the turbidity' or the depth of the water or long-continued stagnation and fouling of the water. 

The few reefs of the Green River formation that have 

been traced in the field serve to illustrate their probable 

variety of form. Some of these, 2 meters (6 feet) or 

more thick, cover only a small area and end abruptly; 

others cover many square miles and apparently thin 

progressively toward the borders. Most of the reefs 

are of this bedlike type. On a few there are portions 

that rise above the general level of the reef as much as 

1.3 meters (4 feet). This relief evidently existed until 

reef building ceased, because the bedding of the overlying shale conforms to the marked irregularities of 

the reef surface and laps up tangentially against the 

steepest sides of these high parts. 

The under surfaces of reefs conform to the substrata, which, unless they are algal, are practically 

flat.. An exception to this rule, however, is found in a 

II Pollock, J. B., Michigan Acad. Sci. Twentieth Ann. Rept., p. 24:l, 1918. 

II Baumann, Eugen, Die Vegetation des Untersees (Bodensee): Archiv Hydro· 

biologie u. Planktonkunde, SuppI. Bd. 1, pp. 26-31, pI. 11, 1911. 
ALGAE REEFS AND OOLITES OF THE GREEN RIVER FORMATION 207 

reef in Sweetwater County, Wyo., which apparently 

filled a rather broad and shallow depression in the lake 

bOtt0111. Its upper surface is essentially leve~. 

Small isolated algal heads or groups of them are 

scattered in the beds below 111any reefs. These are 

precursors of the 111ajor reefs, are not connected with 

them, and are not to be confused with rootlike processes that extend downward fr0111 reefs into the underlying rocks, such as those in the Buntsandstein described by KalkowskyY· 

Each reef consists of an aggregate of more or less 

d01ne-shaped or puffball-shaped masses of algal lil11estone. These will be referred to as heads. They may 

be entirely separate one fr0111 another, or they 111ay 

be nlerely botryoidal convexities or arches in a continuous layer. (See pIs. 40, A; 44, A; 45, A.) }.10reov('r, each head may be silnple and consist of superimposed SlllOOth, concentric, or slightly eccentric layers, 

or it nul.Y be compound and consist of few to many 

smaller heads which in nearly all reefs are fused together. (See pI. 44, B.) Such slllall heads, particularly if fOl'lllcd by a single species of alga, may represent the growth of individual colonies. But if the 

deposit was f01'lned by a cOlllplex assemblage of algae 

then they represent Illerely areas of 1110re rapid growth, 

and generally, though not invariably, these are somewhat arborescent, are less unifofln in size, and have a 

less regular distribution in the larger head. (See 

pI. 43, A.) 

ORGANISMS AND STRUCTURE 

UNICELLULAR ALGAE 

Many algae reefs of the Green River formation are 

built up of. successive crescentic groups of small, 

closely packed spherica.! or ellipsoidal shells of calcite 

separated by thinner layers of Inicrocrystalline calcite. 

These delicate shells range in diameter from 103 to 122 

Inicrons and consist of a Illosaic of cOlllparatively large 

platelike crystals of clear calcite. In the silicified reefs 

they are filled with small anhedral grains of secondary 

quartz, but in the unsilicified reefs they are enlpty. 

V\There they are closely appressed Illany are caved in on 

one side, greatly distorted, or completely crushed. 

Each delicate limy shell is the UloId of a unicellular 

alga fOl'lned by the precipitation of CaC03 on the 

surface of the living plant through its photosynthesis, 

a pi'ocess by which the plant abstracts CO2 fronl the 

water and its dissolved bicarbonates and thus, by 

diminishing the concentration of the carbonate ion in 

the system, reduces the solubility of the normal carbonate to the point of precipitation. 

These algae are almost identical with Ohlorellopsis 

coloniat(L Reis. Except for a slight difference in the 

size of the cells the original description of the genotype will serve for the algae of the Green River forInation. 

\3 Klllkowsky, Ernst, Oollth und Stromatolith in norddeutsehen Buntsandstein: 

Deutsche geol. OescH. Zeitsehr., vol. 60, p. 112, 1908. 

Genus CHLORELLOPSIS Reis 

Chlorellopsis coloniata Reis 

Plate 32, A and B 

Chlorellopsis coloniata Reis, Kalkalgen and Seesinterkalk aus dem 

rheinpfalzischen Tertiar: Geognostische Jahresh., vol. 

36, pp. 107-109, pI. 3, figs. 1,2, pI. 4, figs. 3-6. Miocene 

lake beds of the Rhine graben, Germany, 1923. 

A free translation of Reis's description is as follows: 

Body perfectly spherical, consisting of a shell of very fine 

interlocking grains of calcite, which is preserved only if filled 

with precipitated microcrystalline calcium carbonate that enters 

it through an accidental rupture in the cell wall (or a break 

formed by swarm spore liberation?). Otherwise the spherical 

cavity is later filled with coarser-grained clear calcite similar to 

the rock matrix. In all occurrences the spheres have approximately the same diameter: the few odd-sized ones range in 

diameter from 110 to 140 microns. * * * The spheres occur 

mostly in colonies, more rarely in a series or row, commonly without definite arrangement in little low heaps, often, however, also 

in structures with steep and even overhanging sides; they might 

therefore have been held together in a jelly. They are found, 

nevertheless, in niches, little pits, and depressions in various 

kinds of limy growths * * * but never in the detrital 

grains around them; they often also occur in protected places, 

as the insides of snail shells. They are alwa:vs separated from 

the substratum and from each other, but the spacing is not 

regular. . 

The spheres occur not only in groups by themselves that are 

separated by thin limy layers by also sporadically associated 

with all the other kinds of algae in the Miocene Tertiary marls 

of the Rhine lake basin, although more rarely in beds containing 

solely marine animal remains or in the fine-grained limestones 

intercalated with them. 

Living spherical algae of comparable size are Halosphaera 

(marine), Eremosphaera (100 to 145 microns), Chlorella, which 

lives in marine lower organisms and of whose species Chlorella 

infusiomtm is of the same size as our fossil. The marine Palmophyll'um should be related to Chlorella. It forms a rounded 

and lobate thallus of unicells held together in a jelly which is 

attached to calcareous algae, etc. 

The spherical shells in the reefs of the Green River 

formation range in diameter from 103 to 122 microns 

and so are only slightly smaller than these and surely 

not so different as to determine fl.nother species. 

Their mode of preservation is slightly different, and 

they have not yet been found in sp.ail shells, but the 

identity of the Green River alga with Ohlorellopsis 

coloniata Reis seems beyond question. 

It was perhaps somewhat mislea~ing to compare 

Ohlorellopsis coloniata with the living Ohlorella infusionum, because of the confusion that exists in the 

nomenclature of the living algae. Beyerinck,14 who 

without apparent reason proposed Ghlorella to supersede loochlorella Brandt, described Ohlorella 'in/usionum as free living, never in fanlilies, \vith small cells 

(1 to 4 microns) which are often flattened and rarely 

short cylinders. Furthermore, Beyerinck 15 regarded 

this alga as identical with Ohlorococcum i~fusionum 

II Beyerinck, 1\'1. w., Culturversuebe mit Zooehlorellen, Liehenengonidien und 

anderen neideren Algen: Bot. Zeitung, vol. 48, p. 726, 1890. 

16 Idem, p. 758. 
208 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1928 

(Schrank) Mengehini as described by Rabenhorst,16 in' 

spite of the fact that his and Rabenhorst's descriptions are utterly different. However, OhZorococcum 

i'fltfusionum (Schrank) Mengehini as described by 

Rabenhorst 17 agrees rather closely with the fossil alga, 

and hence it seems to the writer unfortunate that the 

fossil should have been likened to GhZoreZZa infusionum 

Beyerinck rather than to OhZorococcum i'fltfusionum 

(Schrank) Mengehini. Consequently the name OhZoreZZopsis Reis is also unfortunate, for, although it does 

not necessarily imply consanguinity with the living 

plant, it nevertheless links the fossil to some extent 

with a doubtful genus which' the species coZoniata 

resembles considerably less than it does OhZorococcum. 

For comparison a translation of Rabenhorst's 

description of OhZorococcum i'fltfusionum 18 is given 

below. 

Aquatic, green, mucous; cells perfectly globular, size exceedingly variable; integument hyaline, distinct, thick, concentrically laminated; cytoplasm suffused with chlorophyll, homogeneous, and dark olive color, forming a great number of 

gonidia. 

Diameter of cells, all the way up to [usquel 0.0045 inch 

(114.3 microns). 

Habit, everywhere in stagnant water, either affixed to submerged bodies OF free floating. 

Collins 19 says of t1;te habit of this alga that its cells 

are loosely tmited into light-green gelatinous masses 

·that are attached to submerged objects but are easily 

scattered. 

Although there is a strong resemblance in form and 

habit between the fossil algae and OhZorococcum 

i'fltfusionum (Schrank) Mengehini~ their mode of reproduction and color are unknown, and therefore their 

systematic position must remain uncertain. 

FILAMENTOUS ALGAE 

Indisputable calcite mol4s of filamentous algae have 

not been found in the reefs of the Gre'en River formation, although in a small partly silicified area of an 

algae reef from the "Manti be~s," probably a part of 

the Green River formation, there is a network of slender branching white lines, which are circular in cross 

section and whose' algal origin can be demonstrated. 

They are embedded in a translucent matrix and can 

be seen to best advantage in a polished specimen. (See 

pI. 33, G.) A thin section of this area showed that 

the white lines consist of an interlocking aggregate of 

irregular microscopic granules of chalcedonic quartz 

and that the matrix is microcrystalline or almost cryptocrystalline calcite. 

Although these fm!sils show cellular structure in 

places and very probably represent more than one 

16 Rabenborst, Ludvico, Florae Europae algarum aqae dulcis et submarinae, 

vol. 3, p. 57, Leipzig, 1868. 

17 Idem, p. 57. 

18 Idem, p. 57. 

19 Collins, F. S., The green algae of North America: Tufts College Studies, vol. 

2, No.3, p. 144, 1909. 

genus, they can not be positively identified and are 

therefore provisionally referred to the indefinite form 

genus Gonfervites Brongniart. 

Genus CONFERVITES Brongniart 


Confervites rnantiensis Bradley, n. sp. 


Plate 33, A 


Filaments consisting of a single series of cells, straight 

or slightly curved, tips rOl,lnded or bluntly tapered, 90 

to 138 microns in diameter and 0.5 to 1.25 millimeters 

long. Most are simple, but some are sparsely branched 

at rather wide angles, resembling many Confervae. 

SevEfral of these quartz filaments contain centrally 

placed, short chains of excellently preserved cells of an 

alga resembling Nostoc. These cells range from 39.4 

to 67 microns in diameter and 27.5 to 50 microns in 

length and apparently represent more than one species. None of them are brancJ:1ed, and only one contains a cell that seems clearly to be a heterocyst. The 

uniform zone of silica between the chains of cells and 

the microcrystalline calcite apparently represents a 

. gelatinous sheath around which the calcite was precipitated. Presumably the silica replaced the organic 

structure subsequent to the formation of ~he calcite 

mold and apprently so late that only fragments of the 

plants remained. (See pI. 33, A.) There are also 

fragments of filaments. which have short cylindrical 

cells and suggest some of the Oscillatoriaceae. 

Associated with Gonfervites mantiensis are many very 

well preserved though' small coprolites. (See p. 33, 

B.) They are cylindrical, have irregularly or squarely 

truncated orrounded ends, are of various lengths, and 

range in diameter from 38 to 77 Ihicrons but are 

mostly about 60 microns. Some are compact and 

dense, but many of them consist of a close mesh of 

ragged, irregular or dendroid opaque particles resembling organic tissue that has been very strongly macerated. A few consist of more or less loosely aggregated 

black sub angular to spherical particles about 1.5 to 2 

microns in diameter. 

SPONGY STRUCTURE 

Several algae reefs of the Green River formation contain zones of radially arranged thin bifurcating lines of 

clear calcite, more coarsely grained than the matrix, 

which may be casts of filamentous algae. (See· pI. 

34, B.) However, most of the reefs or parts of thenl, 

which show these zones in places, consist of spongy 

or porous masses of microcrystalline calcite which, 

aside from forming crescentic or mammillate layers,. 

show no systernatic structure. (See pI. 34, A.) 

Deposits of this kind seem to he exactly comparable 

to that formed within the dense felt of algae in the 

reefs now growing in Green Lake, N. Y., and in other 

recent fresh-water algae reefs as described by Clarke,20 

20 Clarke, J. M., Tbe water biscuit of Squaw Island, Canandaigua Lake, N. Y.: 

New York State Mus. BUll. 39, pp. 195-198, 1900. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 32 

A. PHOTOMICROGRAPH OF A THIN SECTION SHOWING IN DETAIL THE 


INDIVIDUAL CELLS OF CHLORELU)PSIS COLON IATA RETS 


The walls of each hollow sphere consist. of a mosaic of moderately coarse gra ined calcite 

crystals. The dark matrix is microcrystalline calcil.c. Enlarged 100 diamel.crs 

B . PHOTOMICROGRAPH OF TYPICAL LOBATE COLONY OF CHLOHELLOPSIS 


COLONIATA REIS 


Showing tile vague layering of the unicells. Enla rged 10 diameter. 
U . S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 33 

L , 

A z X 70 

-'r 

A 3 X 7 0 

c X 30 

CONFERVITES MANTIENSIS AND ASSOCIATED COPROLITES 

A . Photomicrographs of cellular ()arts of Con/ervites mantiensis Bradley, n. sp.: 1, Tip of a filament with qu adrate cells and a hluntly ta pered apical cell, resembling some species of L V"Iubua: 2, tip of a fil ament with large spherical cells a nd a wide sheath; 3, filament with in terca la ry heterocyst resemhliog Nostoc. B . Photomicrograph of sm all coprolit.es (a , h, c) in a partly silic ified groundmass of microcrystalline calcite, associated wiLh 61amentous algae in an algae reef from the <I Manti beds." C. Polished speci­ men showing sparse coloJlY of Con/ ervites m antiensis in a partly silici6ed area of aD algae reef from the"M a oti beds." The white areas are calcite ; t be darker ones chal­ cedouic silica 
U. S. GEOLOGICAL SURVEY 	 PROFESSIONAL PAPER 154 PLATE 34 

A . 	PHOTOMICROGRAPH SHOWING THE ASSOCIATION OF THE THREE PRINCIPAL TYPES OF 

STRUCTURE FOUND IN THE ALGAE REEFS OF THE GREEN RIVER FORMATION 

Small area of the reef shown in Plates 43, A, and 45, A. In the lower right-hand quarter is a colony of the large spherical cells of Chlorellopsis coloniata Reis, above that is a thick zone of typical spongy deposit, and at the 

top and also down the left side is an inorganic incrustation. Enlarged 10 diameters 

B. PHOTOMICROGRAPH OF PART OF AN ALGAE 

REEF 

Showing thin radial lines of medium-grained calcite, which may be casts of filamentolls algae. The matrix is a spongy algal deposit of microcrystalline calcite. 

Enlarged 21 diameters. Compare with Plate 30, B 

C. 	 PHOTOMICROGRAPH OF TYPICAL PHYSICOCHEMICAL INCRUSTATION OF CALCITE 

Showing the radial fibrous structure interrupted by thin concentric zones of limonite granules. The irregular black layer at the base and the small rounded cushion-shaped area near the cen ter are spongy algal deposits, which appear almost opaque because they consist of calcite that is almost cryp­ tocrystalline. Enlarged 10 diameters 
U. S. GEOLOGICAL SURVEY PROFESSIONAT, PAPER 154 PLATE 35 

POLISHED VERTICAL SECTION OF A CHLORELLOPSIS REEF 

Showing the irregular and vaguely rad ial arraogemellt of the lobate algal colonies; also a part of the oolitic sandstone upon which it rested. The lightest-gray areas are fine-grained 

sandstone. the black grains are oolite grains, and the medium-toned gray areas are fragments of silty limestone, alga reefs, and mud lumps. Natural size 
U. S . GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 36 

A. DEPOSIT FORMED AROUND WOOD BY CHLORELLOPSIS COLONIATA REIS 

Natural sjze 

B. TUBERCULATE OR PAPILLATE EXTERIOR OF THE TYPE CHLORELLOPSIS COLONIATA REEF 

Each tubercle represents a single colony of algae. From the base of the Laney shale member of the Green River formation, NE. ~ sec. 27, T . 25 N ., H. 103 W., Sweetwater County, Wyo. 
U. S. GEOLOGiCAL SURVEY PROFESSIONAL PAPER 154 PLATE 37 

A. TRANSVERSE SECTION OF CHLORELLOPSIS REEF 


Showing the conoidal piLs in section and the thinning of the algal layers toward the pits. Natural size 


B. UPPER SURFACE OF CHLORELLOPSIS REEF 


With conoidal pits showing their relative size and distribution and tbe difference in texture between tbe interior of the pits and the general surface of tbe reef. Natural size 

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 38 

A. TRANSVERSE SECTION OF THE PITTED CHLORELLOPSIS REEF SHOWN IN B 

Showing the cores of sand-filled ringed pits and the conoidal excrescences at their lower ends. This also shows the 

marked thickening of the algal layers between pit cores. Natural size 

B. CUP-SHAPED, RINGED PITS IN THE UPPER SURFACE OF A CHLORELLOPSIS REEF 

Showing their general uniformity of size and arranllement. At the left they a re arranged in fairly definite rowS. The vermiculate surface between the PIts shows best in a small area a little to the eight of the center 
U. S. GEOLOGICAL S URVEY PROFESSION AL PAPER 154 PLATE 39 

A. HEMISPHERICAL HEADS OF PITTED ALGAE REEF 

Showiog that the pit tubes are very nearly verLical, even where they emerge from Lhe side of a head. The pits in the very steep sides of the head ncar the hammer make concave niches with nearly horizontal bottoms. The upper surface of the reef a t this place is wealhered nearly smooth 

B. OVERTURNED AND BROKEN HEAD OF THE PITTED RE ' SHOWN IN A 

This shows, near t.he hammer head , a hole t.ha t cont.ained the nucleus. I t also shows the eccentric growth layers, which may be annual, and Dcaf the lop of the head (the lower edge of Lhe photograph near the center) several open pit tubes. These are indistinct, partly because th.ey are weathered and partly also because they were somewha t overgrown wiLh algal deposits as the reef formed 
u. S . GEOLOGICAL SURVEY 	 PROFESSIONAL PAPER 154 PLATE 40 

A. 	LARGE PITTED REEF CONSISTING OF SEPARATE, CLOSELY SPACED, TURBINATE 

HEADS WHICH REST UPON A BED OF SMALLER ALGAL NODULES 

The nodule hed rests upon medium-grained massive sandstone that is locally cross-hedded. Tbe second 

and third heads to the left of tbe man show fluting. Tbe minimum time required for the formation of 

this reef is estimated at 355 years 

B. POLISHED VERTICAL SECTION OF A CHLORELLOPSIS REEF 

Showing a large nat algal colony in part broken and in part deepl~ indented by a fragment of lime­ stone that fell on it while the deposit was forming. .l£nIarged 5 diameters 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 41 

A. POLISHED VERTICAL SECTION OF A REEF FORMED OF RECUMBENT DISCOID COLONIES 


OF CHLORELLOPSIS COLONlATA REIS 


The colonies ncar the center and upper parts of the specimen show faintly the concentric growth layers, which are convex outward along the radii of the colonies. Natural size 

B . ISOLATED ALGAL HEAD WITH DIGITATE SPONGY STRUCTURE 


Resemhles in form and sculpturing the marine Lithothamnion. Natural size. See also Plate 42, A and B 

ALGAE REEFS AND OOLITES OF THE GREEN RIVER FORMATION 209 

Roddy,21 Jones,22 and others. Jones 23 also illustrates 

clearly a deposit of this type now being formed in 

Salton Sea. 

Although olgae were apparently the active agents 

that locolized the precipitation of the calcium carbonate 

and gave the deposit its characteristic botryoidal fornl 

and eccentricolly layered structure, the resulting reefs 

are not strictly c01nparable to those built up predominantly of casts or nlolds of algae such as OhZoreZlopsis coZoniata Reis or various marine Corallinaceae. 

They £1,1'0 really only pseudomorphs of the original 

botryoidol algol colonies and not fossil algae like the 

others, which retain not only the outward form of the 

colony but also the form and some of the structural 

details of the individual plants. 

PHYSICO-CHEMICAL INCRUSTATIONS 

A few reefs of the Green River formation contain 

layers whose origin is more obscure. These layers consist wholly of tiers of radially" arranged acicular crystals 

of calcite separated by thin layers of granular calcite 

and lilnonite grains and show neither organic structure 

nor the characteristic spongy structure just described. 

(See pI. 34, 0.) ~10reover, these layers appear to line 

cavities in the reefs and in a few places fill shallow 

cracks. They reseInble layers of olgal deposit in thinning and in places wedging out on the steep or overhanging sides of d01ne-shapeaprotuberances, but unlike 

the algal deposits nlany continue as thin incrustations 

into the bott01ns of pocket-like depressions or infolds and 

up the sides of the adjoining excrescences. Furthermore, they differ fr0111 layers that are patently algal 

in tending toward a sinlpler surface fornl where many 

are superinlposed. They fill the invaginations between 

algol colonies and bridge gaps between theIn, and 

above such bridges each succeeding layer becomes nlore 

unifonll in thickness and so smooths out the surface 

contour. (See pI. 45, A.) Where these layers are of 

essentially tinifornl thickness the junction between 

arcuate sections of thmn is virtually a straight line. 

This feature resmnbles agate structure nluch more 

closely than algal structure. ,(See pI. 34, 0.) 

In describing silnilar finely banded agate-bke deposits which coatod gastropod shells Bucher 24 pointed out 

that the insides of the shells were also incrusted and 

that as the' interior of the shell was dark the deposit 

could hardly have resulted from the photosynthesis 

of algae. 

Tho radially fibrous layers in the reefs of the Green 

River formation may perhaps be recrystallized deposits 

localized by algae like Schizothrix rupicoZa Tilden or 

21 Hoddy, n. J., Concrctions in streams: Am. Philos. Soc. Proc., vol. 54, pp. 

24G-258, 1IH5. 

ii Jones, J. C., Quatel'llary climate; Geologic history of Lake Lahontan: Carnegie lnst. Washington Pub. 352, pp. 6-14, 1925. 

i8 Idem, pI. 1, fig. 10. 

U Bucher, W. n., tiber einige Fossilien und tiber Stromatolithbildung im Tertilir 

del' bayerlshehcn Hheinpfulz: Geognostische Jahresh., vol. 26, p. 79, 1918. 

Ohantransia pygmaea (I(utzing) Sirodot, which according to Tilden 25 grow in weak light and deposit calcium 

carbonate. It is also possible that these layers of 

radial acicular crystals were formed by repeated 

exposure to the air, as at the lake shore, where they 

would be alternately moistened with lime-bearing water 

and dried. There is, however, no evidence to substantiate this supposition. It seems llluch more 

probable that they were formed without the assistance 

of plants and represent physicochemical deposits 

formed rapidly upon the algal layers as substrata. 

Bucher 26 has produced thin layers of this kind experimentally and in further support of the hypothesis of 

their inorganic origin points out 27 that they are 

connected by all stages of transition with oolites for' 

which he has adduced convincing arguments of an 

inorganic origin. 

REEFS BUILT CHIEFLY OF CHLORELLOPSIS 

The molds of the simple alga OhZoreZZopsis coZoniata 

make up the greater part of many algae reefs of the 

Green River formation. These reefs have a variety 

of fonns and internal structure. The specimens described below have been chosen as representative of the 

distinctive varieties. 

TYPE CHLORELLOPSIS REEFS 

The typical OhZoreZZopsis deposits (pIs. 35; 36, B) 

form reefs of huge puffball-shaped heads 0.7 to 1.7 

meters (272 to 572 feet) high and 0.6 to 0.7 meter (2 

or 3 feet) in diameter. Th~y also occur as isolated 

elljpsoidal heads 0.3 to 0.9 meter (1 to 3 feet) in {na,ximum dimension and as thin layers of small extent whose 

lower surface is ~at but whose upper surface is vigorously nodose. 

Some of these reefs are inclosed in beds of very fine 

grained oolite mixed with fine sand, some in finegrained current ripple bedded sandstone; others rest 

on limy shale that contains scattered oolite grains and 

are overlain by hard greenish-gray pyritiferous shale 

that shows only obscure bedding. 'iVhite silty limestone contains nodular masses of the type deposit in 

parts of the formation in WY01ning. The surfaces of 

the reefs differ somewhat, but most are irregularly 

vermiculate or verruculose, with protuberances 2 to 

4 nlillimeters high. A few have markedly tuberculate 

surfaces. (See pI. 36, B.) 

Vertical sections of these reefs show that they consist of an aggregate of closely spaced or intergrown, 

very irregular, elongate simple or branched lobes that 

are crudely elliptical in cross section. These range in 

diameter from 2 to 7 millimeters near the base and taper 

slightly to a rounded tip. Some are expanded laterally. 

25 Tilden, .T. E., Some new species of Minnesota algae which live upon calcareous 

or siliceous matrix: Dot. Gazette, vol. 23, pp. 102-103, 1897. 

~6 Ducher, W. n., On oolites and spherulites: Jour. Geology, vol. 26, p. 608,1918. 

~7 Idem, pp. 593-604. 
210 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1928 

into leaf-like forms about 5 millimeters thick and as 

much as 20 millimeters across. The lobes have a 

crudely radial arrangement but no definjte base or 

substratum and are not arranged in definite layers. 

The largest are about 3.5 centimeters long. A few 

branch dichotomously at an acute angle, but most of 

them bear short thick protuberances directed at a 

rather wide angle away from one side. (See pI. 35.) 

Microcry~talline quartz and chalcedony have filled 

the spaces between the lobes of some reefs; fine limy 

oolite grains, fine sand, or silty limestone fill them in 

others. 

,Thin sections show that these lobate bodies consist 

of many successive limpet-shaped colonies of OhZoreZZopsis coZoniata, some of which are very highly arched and 

decidedly asymmetric. (See pI. 32, B.) Their growth 

was evidently periodIC. Each colony represents a 

brief period of growth and is separated from the next 

succeeding colony by a thin even layer of microcrystalline calcite, which was probably deposited without 

the agency of plants in an interval of lessened or no 

algal growth. 

The groups of algal colonies or lobes taper upward 

slightly, pinch and swell, or retain about the same size 

but do not swell out into bulbous or saclike masses 

with overhanging sides, as if they had had plenty of 

space to expand. This restricted habit is due partly 

to their close spacing, and yet in parts of the deposit 

where they are much more widely spaced they retain 

the same habit. Apparently there was also another 

factor that prevented lateral expansion of the colonies. 

If the limy mud or fine oolite and sand grains accumulated nearly as rapidly as the algae grew, then in 

order to maintain themselves they would probably 

have built chiefly upward-expanding if possible, contracting if necessary. Such a Inode of growth would 

account for their irregular tuberoid form. M'oreover, 

the groups of algal colonies are not definitely arranged 

as if there had been a substratum upon which all the 

colonies were established at once and flourished unhindered. Instead their bases are at various heights above 

the base of the reef, indicating that they are not all 

colonies of the same age and that the substratum 

upon which the successive new colonies started was 

continually being raised. 

The fine-grained and sandy oolite beds in which 

some of these reefs occur indicate shallow water activated by moderate currents or waves, for the oolite 

grains, which average about 0.5 miLlilneter in diameter, 

have been transported; they are gently cross-bedded 

and are mixed with fine clean sand that contains fishbone fragments. Locally there are also small groups 

of oolite grains in their original matrix, indicating that 

the jelly-like ooze in which they were formed had at 

least partly solidified before the grains were disturbed 

and transported. The grains within these small pieces 

of dense calcite do not touch one anot.her but appear 

to have been suspended. Coarse angular mud flakes 

and considerable limonite in the oolite beds suggest 

also that the water was very shallow. At other places, 

however, quieter water is indicated, as the reefs rest 

upon limy shale with oolite grains and are covered by 

shale. 

One zone of ellipsoidal heads and nodules of this 

type was found approximately at the top of the basal 

unit of the Green River formation at the southwest 

corner of sec. 30, T. 1 N., R. 95 W., Rio Blanco County, 

Colo. A reef of great puffball-shaped heads occurs 

also in the upper part of the basal unit about 101 

'meters (330 feet) above the base of the formation along 

the road frOln Fruita to Rangely near the divide between Douglas and East Salt Creeks, Colo. A layer 

of discrete ellipsoidal heads from 4 to about 25 centimeters in diameter, of a very porous algal deposit of 

this kind, occurs between a large pitted algal reef and 

a thick, massive medium-grained sandstone bed in the 

NW. ~ SEe ~ sec. 26, T. 4 N., R. 96 W., Moffat 

County, Colo. (See pl. 13, A.) In Sweetwater County, 

Wyo., in the NE. 3i SW. 3i sec. 14, T. 25 N., R. 103 

W., there is a reef of this type at the base of the Morrow Creek member of the Green River formation. 

Subangular fragments of a silicified reef were found in 

a remnant of coarse bench gravel at the top of the 

Tipton tongue of the formation at the north quarter 

corner of sec. 1, T. 24 N., R. 100 W., Sweetwater 

County, Wyo. The horizon which these pieces represent is unknown. 

MODIFICATIONS OF THE TYPE 

An unusual algal deposit whose internal structure 

is closely similar to the type just described was also 

found in Sweetwater County, Wyo. It formed dense 

incrustations around logs and branches, and some of 

the incrustations were as much as 60 centilneters 

(2 feet) in outside diameter, 20 to 25 centimeters (8 

. to 10 inches) in inside diameter, and 1.8 to 2.4 nleters 

(6 to 8 feet) long. The outer surface of the deposit is 

minutely nodose or papillose. The surface next the 

wood hears a very sharp impression of the woody 

fibers and in places has retained the cellular structure. 

(See pI. 36, A.) Apparently the bark had fallen away 

and the wood had started to decay, as is shown. by 

the crudely rectangular depressions which the limy 

deposit filled. Thin sections of the deposit show that 

it consists of lobate colonial groups of OhZoreZZopsis 

coZoniata that are of the same form as those of the 

type deposit but have a definite radial arrangem~nt. 

Microcrystalline calcite that contains scattered angular grains of fresh plagioclase feldspar fills the interstices between the lobes and also obscures the 

verruculae which the tips of lobes would otherwise 

make. The papillose surface is due simply to differential wet;tthering and is not structural, as inthe reels 

described on page 209. These algal deposits which 
ALGAE REEFS AND OOLITES OF THE GREEN RIVER FORMATION 211 

incrusted logs were associated with an irregular reef 

that has a similar internal structure. They were 

found in the Tipton tongue of the Green River 

formation in the SE. ~ sec. 23, T. 25 N., R. 103 W., 

Sweetwater County, vVyo. 

Another algae reef closely related to the type OhZoreZZopsi.s reefs described on pages 209-210 occurs 286 

meters (940 feet) above the base of the Green River 

formation in the NE. ~ SE. ~ sec. 30, T. 4 N., R. 

96 VV., Moffat County, Colo. It forms hemispherical 

heads 1 to 1.3 Ineters (3 to 4 feet) in diameter which are 

made up of concentric "shells" 4 to 6 centinleters 

thiclc The reef rests upon a thick unit of finegrained buff to gray soft sandstone which is current. 

ripple bedded throughout and is overlain by finegrained but somewhat shaly sandstone. The upper 

surface is verrn"iculate or verruculose. The under side 

has a very spongy aspect and consists of closely spaced 

or intergrown subcircular tubercles whose tips arA 

either concave or contain conoidal depressions that 

apparently confornl to the nodose surface of the underlying "shell." A polished cross section shows that 

the reef consists of tiers of radially arranged irregular 

clavate to bulbous groups of OhZoreZZopsis coZoniata 

colonies, some of which are bifid. Most of the spaces 

between colonial groups or lobes are filled with mediu~­

grained sand Inixed with ostracode valves, but some 

are empty, and some contain dense buff calcite, probably of inorganic origin, which is similar to the thin 

layers that separate the tiers of algal colonies. 

PITTED CHLORELLOPSIS REEFS 

Algae reefs with large, distinct pits (pIs. 37, A and 

B; 38, A and B; 39, A and B; 40, A) are apparently 

peculiar to the Green River formation of Colorado. 

They were not found in that formation in Utah nor 

in Wyoming, and as yet the writer has found no mention in the literature of any conlparable algal deposit. 

'Valcott's pre-Cambrian genera Greysonia and Ooppe1'ia 28 contain large tubes. filled with extraneous lnaterial, but in thenl' the part regarded as algal is smallso small, indeed, that the deposits are utterly different 

frOln those of the Green River formation. These 

Eocene deposits fOrIn reefs of considerable extent 

which are 0.3 to 1.8 Ineters (1 to 6 feet) thick and 

consist of closely appressed hemispherical or turbinate 

heads. They are interbedded with algal deposits of 

other kinds or occur between thick beds of clean 

light-gray Inedimn-grained cross-bedded sandstone. 

Circular pits of two distinct kinds cover the upper 

surfaces and in part also the sides of the heads. Those 

of one kind are shallow, cup-shaped, and fairly uniform in size and contain a more or less prominent 

raised concentric ring or collar in the bottonl. In a 

few there are two such concentric rings. (See pI. 

28 Walcott, C. D., Pro-Cambrian Algonkian algal flora: Smithsonian Misc. ColI., 

vol. 04, pp. 108-110, pIs. 1 i-19, 1914. 

38, B.) Within the ring is another pit, circular or 

obovate in section, which is the end of a sand-filled 

tube that extends down into the reef. In some parts 

of the reef the pits are about equally spaced and without definite arrangement, but in other PUTts they have 

a distinct linear arrangement in the rounded bottoms 

of troughs. (See pI. 38, B.) Sharp but somewhat 

sinuate crests separate these troughs. The entire surface is vermiculate and resembles rather closely the 

surfaces of the type OhZoreZZopsis reefs. The under 

side of an eccentric shell of this type of pitted reef 

bears rounded, conoidal excrescences, each with a 

crater-like pit at the top which is the other end of a 

sand-filled tube or core of a surface pit. 

The- pits of the other kind are simply cone":shaped 

depressions with rounded bottoms. They may be 

very shallow or deep: Near the surface the cone 

flares, forming a sort of border for the pit. This collar 

and the inside of the cone have ·a granulose texture, 

which contrasts with the rather coarsely faveolate 

surface of the reef. (See pI. 38, B.) These pits differ 

widely in size and have no regular arrangement, although mo'st of them are about equally spaced. The 

under side of a pitted reef of this type is marked with 

deep crater-like pits in the tops of low, steep· sided cones. 

In cross section the pitted reefs show rather thick 

and porous or cellular growth layers. These consist of fine-grained buff calcite and are arched between 

the pit cores, being more highly arched the more 

closely the cores are spaced. Many pit cores extend 

through at least one "reef shell," 5 to 12 centimeters, 

but others go only about 1 centimeter. below the bottom of the pit. (See pI. 38, A.) The writer does 

not know what the maximum length of these tubes 

may have been. The heads of some reefs are clearly 

fluted for 3 feet or more from the top, and these 

flutings end in ringed surface pits. (See pI. 40, A.) 

Broken fluted hea.ds show that many of the tubes are 

both long and wide. Those shown in Plate 39, B, 

are 2 or 3 centinleters in diameter, only a little smaller 

than the surface pits. 

The tubes of the ringed pits are filled with clean 

fine-grained sand compactly cemented with clear 

calcite. Small fishbones and a few ostracodes are 

scattered through these cores. .The tubes of the conoidal pits are less distinct, having been largely overgrown by algal deposits from the sides and filled with 

small pellets of algal limestone and fine oolite grains. 

Under the microscope the two kinds of pitted deposits appear to be essentially the same. They consist 

of superimposed long botryoidal layers of OhZoreZZopsis coZoniata Reis separated by irregular layers and 

lunate zones of somewhat spongy microcrystalline 

calcite, which shows a network of radially arranged, 

interlacing fine lines of more coarsely crystalline calcite. (See pI. 34, B.) Scattered through this organic 

s~ructure are many small pockets and stringers of 
212 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1928 

angular quartz and fresh orthoclase feldspar grains 

some of which are as much as 0.3 millimeter in diameter. These detrital grains are in a matrix of clear, 

finely granular calcite. 

In certain zones in the reefs the colonies are more or 

less isolated, tall, columnar, and branched and give 

those zones a coarsely spongy aspect. This different 

habit was apparently caused by an accumulation of 

medium-grained sand and cyprid ostracode valves, 

in the hollows between colonies, which nearly kept 

pace with the algal growth. 

In some reefs the algal deposits and also laminae of 

dense structureless limestone that coat them are considerably brecciated. The angular fragments, mixed 

with a generous proportion of fine sand and limy 

ostracode shells, form distinct layers within the reefs. 

Such structure indicates that the limestone of both 

kinds became hard and brittle comparatively soon 

after its deposition and that these reefs grew where at 

intervals waves and currents were active. 

Clearly these deposits grew periodically by the addition of alternate layers of algae molds and precipitates 

of finely divided calcium carbonate. The" algae grew 

freely, for their extensive layer-like colonies also 

expanded upward into comparatively broad domelike 

forms. Filamentous algae apparently also flourished 

and formed somewhat compressed henlispherical colonies among and on top of the ChZoreZZopsis colonies. 

Toward the tubes the colonies thin very decidedly 

and in that way form the tube pits, for obviously the 

area immediately surrounding a tube built up mueh 

less rapidly than the other parts of the deposit. Consequently also the thinned edges of the colonies must 

dip more and more steeply into the pits as the deposit 

increases in thickness. In some reefs these edges dip 

inward at angles as large as 65° from the horizontal. 

The conclusion is inescapable that the immediate 

vicinity of these pit tubes was distinctly less favorable 

for the growth of the lime-depositing algae than areas 

more remote frOlll the tubes. In fact, it appears that 

the growth of the algae was inversely proportional to 

the proximity of pit tubes. 

The reasons for the greatly restricted growth of algae 

near the tubes are not clear. One possible explanation 

is offered. The tubes are all vertical or very nearly 

so, even though they emerge from the very steep sides 

of a large columna.r head of a thick reef. (See pI. 39, 

A.) They are also fairly uniform in diameter, mostly 

0.75 to 1.75 centimeters. None larger than 3 centimeters in diameter have been observed, but in places 

where they are rather closely spaced, as between two 

of normal size, there are tubes as small as 3 millimetersin diameter. This persistentlyvertical habit, the 

variation of size within fairly definite limits, and 

especially the spatial relations of small to large tubes, 

together with their fairly regular circular or slightly 

elliptical cross section, suggest that the tubes are 

molds of a large sedge such as S cirpus lacustris, the 

common bullrush that grows profusely in the shallow 

water along lake shores. If the tubes were formed in 

that way, then the zone around the sedge stems may 

have been less favorable to the algae by reason of 

the reduced illumination at all times except when the 

incident light was practically parallel to the sedge 

stalk. The most luxuriant growth of algae in the 

widest spaces between tubes accords with the suggestion of light control. Sand and other detrital material 

may well have filled the tubes after complete decay 

of the sedges when reef building ceased and the deposit 

was buried by the overlying sediment. 

Although this explanation may serve to elucidate the 

distribution of the algae and consequently also the 

formation of the pits," it is not wholly convincing as to 

the origin of the tubes, because there i; no trace of the 

stout rootstocks of a sedge. Further search lnight 

reveal thenl at the base of the reef, and yet it is 

" inconceivable that a single stand of sedges could have 

persisted while more than 2 meters of algal limestone 

was formed around them. It is, however, barely possible· that the rootstocks grew in the lilllY mud at 

many successive levels in the reefs, and that as they 

were horizontal and below. the surface of the deposit 

they had little chance of being filled with sand, and 

therefore upon decay their molds collapsed and the 

limy mud settled in, thus obliterating all trace of them. 

Even the vertical tubes, where filled with microcrystalline calcite, are exceedingly obscure. 

Although originally all conoidal, the surface pits 

have very probably been nl0dified to the cup shape by 

solution, as \they are excellent small . water reservoirs. 

Moreover, the tops of some pitted reefs are so deeply 

weathered that the pits are nearly effaced. Only 

obscure rings show where the tubes end. (See pI. 

39, A.) Because fine to medium grained, well-sorted 

sand· occurs between the algal colonies, because there 

are layers of finely brecciated algal limestone mixed 

with sand at several levels within the reefs, and because 

many of the reefs rest on sandstone or beds of oolitic 

and ostracode limestone which contain coarse broken 

fragments of algal limestone it seems very likely that 

these reefs were formed in shallow water, where currents and waves were at least periodically aetive. 

As the origin of the tubes can not be conclusively 

demonstrated they do not assist in interpreting the 

reef ecology. 

The thickest and best-exposed pitted reef was found 

near the top of a shore phase of the Green River formation in the NW. ~ SE. ~ sec. 26, T. 4 N., R. 96 W., 

Moffat County, Colo. (See pI. 40, A.) It rests upon a 

thin layer of ellipsoidal algal heads, which in turn 

rests upon a massive bed of light-gray clean mediumgrained sandstone that is about 5.2 meters (17 feet) 

thick. This sandstone bed, together with two others 

below, makes a conspicuous cliff about 15 meters 
ALGAE REEFS AND OOLITES OF THE GREEN RIVER FORMATION 213 

(50 feet) high which is chiefly light gray but is locally 

banded with pink, mauve, and ocher. At approximately the same horizon and only 4 miles farther west, 

in the NE. 34' SE. 34' sec. 30, T. 4 N., R. 96 W., Moffat 

County, Colo., is another algae reef with very sharply 

defined pits. (See pI. 38, B.) This may have been 

formed contemporaneously with the reef in sec. 26 

but is not a westward continuation. It is about 1.5 

meters (5 feet) thick, but only the upper third is 

pitted, the lower part having smooth-surfaced shells. 

'Soft shaly sandstone and siltstone underlie this reef, 

and fine-grained soft light-gray to buff sandstone overlies it. 

Two other pitted reefs were found in the basal unit 

of the formation along the road from Fruita to Rangely, 

near the divide between Douglas and East Salt Creeks, 

Colo. One which is 51.6 meters (170 feet) above the 

base of the formation is only 5 centimeters thick and 

fonns heads 7 to 15 centimeters in diameter. It rests 

upon ostracode limestone and is overlain by finely 

laminated dark-brown wa:A"y shale, which contains 

:sonle ostracodes and numerous small fishbone fragInents and the skeletons of small fish. The other pitted reef is 162 meters (535 feet) above the base and 

ranges in thickness from 0.3 to 1 meter (1 to 3 feet). 

It fonns hemispherical or puffball-shaped heads 15 to 

'60 centimeters in diameter and makes up a part of a 

,compound algae reef 5.5 meters (18 feet) thick,. (See 

pI. 29, A.) 

A Ohlorellopsis reef which is without pits but which 

in configuration and internal structure closely resembles the pitted reefs was found near the base of the formation in the SE. 34' NE. 34' sec. 18, T. 3 N., R. 95 W., 

Moffat County, Colo. It consists of much flattened 

,cushion-shaped heads from 5 to about 20 centimeters 

in dianleter, whose surfaces are snlooth or only weakly 

faveolate, and is associated with regularly bedded ostracode liJnestone, oolite, sandstone, and shale. Each 

head of the reef is built up of many layers of Ohlorellopsis coloniata separated by very thin layers of dense calcite. Thus the algal colonies are very extensive, some 

having areas of 1nore than 1,000 square centimeters. 

1\10st of them are less than 5 millimeters thick, and 

none are nlore than 7 millimeters thick. Some consist of a single even layer of cells, but most, of them are 

many cells deep and are minutely mammillate. 

These colonies illustrate well the effect of contemporaneous accumulation of small a1nounts of detrital 

material and also indicate that the cells of Ohlorellopsis coloniata were invested in a gelationus integunlent. 

.several algal layers, otherwise almost perfectly smooth, 

are deeply indented by pockets filled with subangular 

limestone pellets, fine sand, oolite grains, and ostracode valves. Some of the largest limestone fragments, 

about 4 milli1neters long, stand with their major axes 

nearly vertical and their lower ends resting in sharp 

,downfolds of algal colonies. (See pI. 40, B.) Evidently the investing medium of the algal cells was 

tough enough to bend sharply without breaking. 

REEFS OF RECUMBENT COLONIES 

Large recumbent Ohlorellopsis colonies form reefs of 

closely appressed spheroidal. heads which are 6 to 8 

centimeters thick and 12 to 20 centimeters in diameter. Locally these heads have the'form of short roundtopped columns as much as 30 centimeters high. Moderately soft light chocolate-brown shale which weathers 

mouse-color underlies and overlies these reefs. The 

upper surface of each head bears closely ,spaced irregular cushion-shaped protuberances 0.5 to 3 centimeters 

in diameter and about 0.5 centimeter high. The sides 

have peripherial wrinkles or folds that vaguely resemble 

fabric, and the bottoms are practically smooth. A 

vertical section through a head shows that the deposit 

is built H,p of large recumbent colonies of Ohlorellopsis 

coloniata. (See pI. 41, A.) These are exceedingly irregular, but most of them are discoid layers which range 

from about 1 to 6 centimeters in diameter. They 

average about 0.5 centimeter in thickness, but a few 

are as thick as 1 centimeter. ,Their eccentric growth 

lines are convex in- the direction of the radii of the 

colonies except in those colonies that form the surface 

layer, in which the growth lamellae are convex upward. Most of the colonies .are separated by very 

thin, mildly brecciated layers of light-buff dense calcite. Between some of them are thin irregular layers and lenses of contorted chocolate-brown shale 

similar to that upon which the reef rests. 

Thin sections of these colonies show that many of the 

Ohlorellopsis cells are ellipsoidal but apparently only 

because they are so densely packed. The cells are 

embedded in a micro granular matrix of calcite which 

was originally rather porous. Secondary quartz in 

sIl1all interlocking grains now fills the pores. Also the 

thin sections show that the thin buff layers consist of 

transversely arranged calcite crystals and that the 

brown shale contains enough organic matter to be 

regarded as a low-grade oil shale. 

Why the algae in these reefs formed such unusual 

colonies !s not wholly clear. So decided a tendency 

toward the formation of discoid colonies by peripheral 

growth seems to indicate that free vertical growth was 

inhibited. The-inhibition may have been due to the 

deposition of a thin film of organic ooze or the precipitation of a thin layer of calcium carbonate on the upper 

surfaces of the colonies. Perhaps also the overlapping 

of contemporaneous colonies prevented upward growth. 

On the other hand, the mildly brecciated linlY layers, 

together with the gently contorted organic shale, suggest that the basement yielded under the weight of the 

growing colonies so that they were unable to assume 

their normal cushion or puffball shape. A somewhat 

higher concentration of dissolved salts in the lake 

water of that stage might also have in part caused the 
214 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1928 

peculiar habit of the algae in these reefs. Th~y are 

associated with beds of sun-cracked shale and at least 

one bed of rather low-grade oil shale which contains 

many small calcite pseudomorphs after glauberite. 

Although the salinity of the water might have increased 

enough to modify the habit of the plants, the supposed 

change was probably not great, for the form and size 

of the cells remained unchanged. The bulbous colonies of the surface layer indicate more normal conditions of growth and also serve to de~onstra;te that 

the recumbent habit is not a character upon which to 

found another species of Ohlorellopsis. 

These algae reefs were obviously formed in quiet 

water, but at what depth it is inlpossible to say except that it must have been shallow enough to promote active photosynthesis in the algae. Theywere 

found at the base of the saline facies of the Green 

River formation in the composite section m~asured in 

Indian Canyon along the Inail road f.rom Duchesne to 

Price, approximately in sec. 28, T. 6 S., R. 7 W. 

Uinta meridian, Duchesne County, Utah. One reef is 

about 1,063 meters (3,830 feet) and the other about 

1,185 meters (3,900 feet) above the base of the 

formation. 

A thin partly silicified reef consisting of a few layers 

of recumbent Ohlorellopsis coloniata colonies was found 

in the basal tongue of the Green River formation just 

north of Soldier Summit, Utah County, Utah. These 

colonies range in diameter from 0.5 to about 4 centimeters, but very few exceed 3 millimeters. They rest 

either upon a very uneven substratum apparently 

made up of heaps of plant detritus mixed with ostracodes and mollusk shells or upon thin irregular zones 

of spongy algal deposit whose interspaces have been 

filled with chalcedonic silica. Some' of the Ohlorellopsis 

molds are filled with silica, others with yellowish microcrystalline calcite. In the partly silicified debris 

which the algae incrusted were found large pieces of 

the tissues of higher plants, cuticles of leaves, various 

pollen grains, and numerous short fungal hyphae, sonle 

of which bear simple terminal conidia. Thin and 

somewhat contorted layers of yellowish-brown limy 

shale are also included in the deposit. Stems of Ohara, 

but no fruits, are fairly plentiful in a silicified layer 

associated with the algae reef. Clearly this reef formed 

in quiet water, which was probably 'also shallow and 

close to a protected shore. 

REEFS WITH SPONGY STRUCTURE 

DIGIT ATE REEFS 

A specimen representing an unusual type of reef 

occurs either as isolated spheroidal or potato-shaped 

heads or as large botryoidal intergrowths of these 

forms and is embedded in light-brown ~aky or platy 

sandy shale whose beddIng is somewhat contorted. 

(See pI. 41, B.) It is overlain by a bed of massive 

hard greenish-gray shale that contains many secondary 

gypsUln partings. The upper surface bears many irregular mound or ridge shaped excrescences separated by 

rather deep depressions, which are partly filled with 

buff limy mudstone. In addition to these larger features the upper and lower surfaces are vigorously 

tuberculate or papillate. The steep sides are granular 

or pustulate. In its form and sculpturing it resembles 

closely aspecimen of Lithothamnium? ellisianum described by Howe and Goldman.29 

A polished vertical section of this specimen, however, shows that the heads of the reef consist of many 

digitate groups of interrupted cuneifornllobes of finely 

crystalline calcite which show fine arcuate growth 

lines delicately colored in tints that range fronl deep 

reddish brown to buff. (See pI. 42, B.) Very fine 

grained dark bluish-gray to creanl-colored limy sandstone fills compactly the spaces between the calcite 

lobes or columns. Clear crystalline calcite fills some 

of the cavities that were apparently not open enough 

to permit the sand to enter. . 

A transverse section of this specimen shows that the 

lobes or columns are arranged in a roughly concentric 

manner and that although they are exceedingly irregular in cross section' they show a marked tendency 

toward centrifugal thickening, especially in those near 

the periphery. (See pI. 42, A.) The smaller columns 

are simple and nearly circular in cross section, but the 

larger ones are deeply and complexly embayed. 

The internal structure of this reef resembles rather 

closely an algal deposit from the north Gernlan 

Buntsandstein at Schlossenberg described by Kalkowsky.30 It also resembles the algae reefs now being 

formed in Gteen Lake, N. Y. 

Thin sections cut parallel to the columns reveal in 

them obscure algal forms. The plainest of these are 

several transverse zones of Ohlorellopsis coloniata 

molds. Other parts of the columns or algal colonies 

consist mostly of microcrystalline calcite which locally 

has a spongy structure resembling that of certain 

recent algae reefs, but there are also areas of unifonnly 

fine granular calcite that shows no other structure 

than vague growth layers.. The obscurity of the plant 

structure in this specimen seems to be due chiefly to 

lack of differentiation in size of crystal grain between 

the plant molds or casts and the matrix. 

This reef is peculiar not only in its complex, digitate 

habit of growth but also in its content and distribution 

of organic matter and limonite grains. Each algal 

colony and branch has just beneath its surface a thin 

layer of closely packed fine limonite granules, many 

of which are cubical. Locally the granules are also 

scattered sparsely through the interior of a colony. 

Associated with the limonite or distributed in skeleton 

29 Howe, 1\1. A., and Goldman, M. I., Lithothamnium? ellisianum, sp. nov., 

from the Jurassic Ellis formation of Montana: Am. Jour. ScL, 5th ser., vol. 10, p. 

316, 1925. 

80 Kalkowsky, Ernst, Oolith und Stromatolitb in norddeutschen Buntsandstein: 

Deutsche geol. Gesell. Zeitschr., vol. 60, pp. 106-107, pl. 8,1908. 
ALGAE REEF'S AND OOLITES OF THE GREEN RIVER FORMATION 215 

forms of tall algal colonies within the limonite encasements is a considerable quantity of yellowish-brown 

organic nlattel'. It is not honlogeneous, but neither 

does it contain identifiable organisms. It resembles 

the organic matter of oil shale and is still further 

cmalog6us to such matter because it is diffused through 

microgranular calcite. This reef derives its colors 

frOln the limonite and organic matter. 

Apparently the limonite is secondary after pyrite 

that formed from decomposition products of the 

organic matter find iron salts dissolved in the lake 

water. 1101'eover, the organic matter is probably a 

residuum of the plants that built the reef, not only 

b('(~nuse it has the fonn of algal colonies but also 

because the deposition of an organic ooze upon the 

reef would hardly be expected in water continually 

transporting and depositing sand. Furthermore, the 

segregation of the linlonite close to the peripheries of 

colonies suggests that the inclosed algae subsequently 

decayed and that as hydrogen sulphide from their 

decay migrated outward it precipitated pyrite where 

it canle into contact with iron salts in the lake water. 

The occurrence of disseminated limonite granules 

within some colonies is also in harmony with this 

hypothesis. 

This particular specimen shows two nlajor stages in 

the history of the reef's developnlent. At a, Plate 42, 

lJ, is an irregular nucleus of dense cream-colored 

cfiJcitc fronl which finely laminate colonies radiate. 

A buff band, shown in white in the photograph, circumscribes the nucleus and passes through the tips of the 

colonies that ra,diate fronl it. The colonies directed 

downward fronl the nucleus are much longer than those 

directed upward. Because they grew principally 

upward by accretion of calcite at their tips it is evident 

that the part of the reef circumscribed by the buff 

band was overturned when it had reached that stage 

of its development. A sinlilar but less striking nodule 

cut so as to just nliss the nucleus may be seen to the 

right of this one. (See pI. 42, B.) There are also 

smfill short ·colonies on what was the under side of the 

larger nodule. '''hether these grew downward where 

the nodule did not actually rest on the bottonl it is 

difficult to say. The absence of thenl on the originally 

lower side of the smaller nodule lends slight support 

to this idea. 

The second stage in the developnlental history of 

this specimen is represented by the tall flabellate 

colonies that :make up the larger part of the specimen. 

They are oriented as they grew. (See pI. 42, B.) 

'Ih is reef is so silnilar to those now being formed 

in Green Lake, N. Y., that it seems safe to infer for 

it a like origin. The tall flabellate and complexly 

branched protuberfinces whose tips are richly nodose 

arc rC'l11firkably like those of the recent reefs find like 

them were probably formed through the agency of 

a dense felt of algae. The elongated protuberances 

of the recent deposits seenl to be due to rapid growth 

and a struggle of the plants to acquire better illumination. Sinlilar features in the fossil reefs seenl properly 

to be explained in the same way. The overturning 

of these nodules when partly fonlled indicates at 

least periodic strong wave action, and the abundance 

of fine, well-sorted sand between the arborescent 

masses also indicates current or wave action. FrOlll 

these the writer concludes that this reef was formed 

in fairly shallow water. 

This reef was found approximately in sec. 22, T. 

10 S., R. 25 E., Uintah County, Utah, about 82 

meters (270 feet) above the base of the Green River 

formation. 

TABULATE REEFS 

Tabulate reefs of essentially uniform thickness 

occur within beds of fine-grained and somewhat 

shaly oolite, which also contains numerous ostracodes. (See pI. 43, B.) At one locality a reef of this 

kind contains vertical nlOlds of ltlrge deeply fluted 

Equisetum stems. The top consists of slightly arched, 

very irregular, and lllore or less closely appressed 

lllolariform or renifornl protuberances, which are 

yellowish buff. Small oolite grains in a dense gray 

matrix occupy nlost of the depressions between these. 

The lower surface of the reef is practically flat. 

As shown in the polished cross section the reef is 

built up of nlany rather thick layers of porous yellowish-gray calcite. These layers are only slightly 

sinuous near the base but become more arid lllore 

irregular towa.rd the top, where they fornl a series 

of flat-topped, steep-sided arches separated by deep 

channel-like depressions that are pa.rtly filled with 

fine oolite grains cenlented by light-gray calcite: 

Such deep crooked channels give the cross section 

of the reef a crudely columnar aspect. 

Vertical thin sections of a reef of this type show 

that the rather poorly defined layers consist of microcrystalline calcite and have a spongy structure. 

The microcrystalline calcite contains thin branching 

lines of slightly coarser grained calcite which have a 

prevailing radial habit. (See pI. 34, B.) SOlIle of 

these nlay be the casts of filanlentous algre, but others 

clearly are not, for they fork downward as well as 

upward and form a continous network between the 

irregula.r nlicrocrystalline nlasses. Furthermore they 

are not at all unifornl and widen into comparatively 

large cavities, which differ greatly in size and have no 

definite form. These coarser-grained calcite lines 

seen rather to be cross sections of thin secondary 

fillings between the lllicrocrystalline calcite 111asse"s. 

lVloreover, thin sections cut normal to these fine 

radial lines that nlost 'resemble algae support this 

hypot.hesis, for none of thelll are circular or even 

elliptical in cross section. They entirely surround 

t.he t.ransverse sections of columnar and globular 

nlicrocrystalline nlasses that nlake up the reef. 
216 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1928 

The spongy but otherwise structureless aggregate of 

microcrystalline calcite is exactly comparable to the 

deposits of calcium carbonate localized by members of 

the Cyanophyceae at the present time in fresh-water 

lakes, and very probably it had a similar origin. Small 

calcite oolite grains which apparently formed where 

they are now found are associated with reefs of this 

kind and indicate that the water, for a time at least, 

was saturated with respect to calcium carbonate. 

Vertical molds of . large Equisetum stems occur in one 

reef. These evidently grew contemporaneously with 

the reef and show that the deposit formed in very 

shallow lake margins, where a more or less sparse 

emergent vegetation prevented not only strong water 

movements but also the influx of much clastic material. 

Although shallow, the water was probably clear except 

at times of storm, when the limy mud was thrown into 

suspension. Such shallow and slow-moving water 

must also have been considerably warmed, a condition 

favoring the formation of the oolitic marl in which this 

type of reef occurs. 

One reef of this kind was found at the base of the 

Laney shale member of the Green River formation in 

the NW. 7.;t sec. 18, T. 25 N., R. 103 W., Sweetwater 

County, Wyo. A similar reef occurs in Colorado near 

the top of the basal unit of the formation, about 161 

meters (530 feet) above the base, on the divide between 

East Salt and Douglas Creeks a few hundred feet east 

'of the saddle through which the Fruita-Rangely road 

passes. This land has not been sectionized, but the 

locality is approximately where sec. 13, T. 5 S., R. 

102 W., would fall. 

COMPOUND REEFS 

Reefs built up of more than one principal structural 

type have been grouped for convenience of exposition 

un,der the general term compound reefs. They may 

include not only Chlorellopsis colonies, Oonfervites 'filaments, and the less definite nlasses with spongy structure but also physico-chemical incrustations. 

REEFS CHIEFLY ALGAL 

Compound reefs that are chiefly algal were found in 

beds of limy shale as isolated, more or less widely spaced 

low circular heads that are somewhat biscuit or mushroom shaped, 3 to 8 centimeters high, and 5 to 18 

centimeters in diameter. The upper surface and sides 

consist of a mosaic of smaller heads, which are irregularly rounded or elliptical but somewhat flattened or 

even concave on sides where they are closely appressed. 

Although the l1pper surface was worn nearly smooth 

by scour before burial, each minor head was originally 

bulbous and represents an Individual algal colony. 

(See pI. 44, B.) Along the nlargins where abrasion 

was less these are now wartlike protuberances. The 

under surface has the form of an inverted irregular 

basin with a nearly flat bottom and steep or even, 

oyerhanging sides. 

A polished cross section of a specimen representing 

this type reveals four growth zones, each with it distinct structure. (See pI. 44, A.) The lowest zone has 

a spongy structure and consists of dense brownish-gray 

calcite. The interspaces are completely filled with 

clear coarsely crystalline calcite, which is evidently 

secondary. The second zone is considerably thinner 

and consists of dense calcite finely color banded in 

shades of red-brown, yellow, and gray. This zone is 

more compact than the others and closely resembles, 

agate. Overlying the agate-like zone is a layer which 

has a spongy structure somewhat similar to that, 

of the basal layer except that the areas of dense, 

calcite are larger and light buff. In places they are, 

radially elongated and give the zone a very crude columnar structure. Many of the elongated pieces are 

distinctly arborescent. Some of the interspaces of 

thin layers have been filled with clear calcite, but most 

of them are still open. The structure of both spongy 

zones is very much like the internal structure of the 

algae reefs now being formed in Green Lake, N. Y. 

The surface layer consists of rather large and irregular 

bulbous or puffball-shaped colonies of Chlorellopsis 

coloniata Reis, which rise from a nearly continuous 

substratum of the same organisms. (See pI. 44, A.) 

These colonies are about 1 centimeter high and range in 

diameter from 4 millimeters to 1.7 centimeters. Some 

are irregular sprawling forms, and a few are forked 

near the summit, but most of them 'are simple. All 

contain thin irregular stringers or clavate lobes of 

dense buff calcite in which the plant cells occur only 

sparingly. 

Areas between the algal colonies are filled with dense 

brownish calcite that shows fine laminae outlining the 

colonies. Between some colonies are pockets of fine 

sand mixed with a few small ostracode valves. 

Under the microscope the two spongy layers separated by the agate-like zone appear to be identical 

except only that more interstices of the'lower one 

'contain coarsely crystalline secondary calcite. The 

irregular and somewhat arborescent masses that make 

up these layers consist of even-grained microcrystalline cttlcite, which locally contains a few fine interlacing lines of more coarsely crystalline calcite that may 

may be the casts of filamentous algae. The agatelike layers consist mostly of tiers of radially elongated 

calcite crystals, but locally the whole zone is made up 

of finely granular calcite. Minute granules of limonite 

are scattered thrQugh this zone or are arranged in 

definite layers. These layers, perhaps together with 

small quantities of organic matter, give to the zone its 

banded aspect and various shades of red, brown, and 

gray. Many of the limonite granules are cubical, and 

probably all are secondary after pyrite. In the micro­
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 42 

A. POLISHED TRANSVERSE SECTION OF THE DIGITATE REEF SHOWN IN B 


Natural size 


B. POLISHED VERTICAL SECTION OF A DIGITATE ALGAE REEF 

Showing nuclei of dense cream-colored limestone (a) and two distinct stages of growth. The light-gray finely speckled material between the columns of algal deposit is fine-grained limy sandsLone. Natural size 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 43 

A. UPPER SURFACE OF A COMPOUND REEF WHICH CONSISTS OF ALTERNATING ZONES OF ALGAL AND 


INORGANIC LIMESTONE 


Ncar basc of Tipton Longue of Green River formalion in NW. J4 sec. 21, T. 24 N .. R. 101 W., Sweetwater County, Wyo. Three­ fourths nat.ural size 

B. UPPER SURFACE OF A TABELLATE REEF WITH SPONGY STRUCTURE 

Each molariform head is more or less columnar in section, though maoy of them arc very irregular and complexly intergrown. 
 Three-fourths natural size 

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 44 

A. POLISHED VERTICAL SECTION OF A COMPOUND ALGAL HEAD CONSISTING OF MANY SMALL HEADS, EACH OF 


WHICH REPRESENTS A SINGLE COLONY OF CHLORELLOPSIS COLONIATA HEIS 


These mioor heads rest upon a zone of spongy algal deposit, which is separated from another similar zone below by a finely banded inorganic agatelike zone. Nat.ural size 

B. COMPOUND ALGAL HEAD CONSISTING OF MANY MINOR HEADS, EACH OF WHICH HEPHESENTS A SINGLE COLONY OF ALGAE 


Compare wiLh A 

U. S. GEOLOGICAL SURVEY 	 PROFESSIONAL PAPER 154 PLATE 45 

A. 	POLISHED TRANSVERSE SECTION OF THE REEF SHOWN IN PLATE 43, A, SHOWI 

AND INORGANIC LAYERS 

The irregular light-colored layerS consist or the molds or ChloTellopsis coloniata and typical spongy algal deposit. The black and gray finely banded layers are of inorganic origin and owe their dark color to disseminated pyrite. Enlarged 3 diameters. 

Compare with the photomicrograph of a thin section of part of the same reef shown in Plate 34, A. 

B. ALGAE REEF FROM THE "MANTI BEDS," MANTI, UTAH 


The dark areas are partiy silicified and contain the filamentous a lgae and coproliLes shown in Plate 33. Natural si,e 

U. S. GEOLOGICAL SURVEY 	 PROFESSIONAL PAPER 154 PLATE 46 

A. 	POLISHED SECTION OF AN ALGAL COBBLE B . ALGAL PEBBLES FORMED CHIEFLY OF CHLORELLOPSIS COLONIATA REIS 

IN A MATRIX OF OSTRACODE LIMESTONE Showing a large subangular limestone nucleus and three distinct stages of growth. Natural size. See text, p. 219, for explanation of let.ters Natural size 
POLISHED SPECIMEN OF ALGAL PEBBLES SHOWING DETAILS OF INTERNAL 


STRUCTURE 


A~ a is a pebble consis~i g wholly of Chlorellopsis coloniata, a t band c a re pebbles made up chiefly of 

Ch lorellopsis molds but conta ining also thin dense inorganic layers, and a t d is a pebble consist­ ing chiefly of spongy algal deposit with a rew thin inorganic layers a nd a rew Chlorellopsis 

molds. Betwoon the algal pebbles are small oolite grains mixed with fine limy sand. Enlarged 

5 diameters 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 154 PLATE 48 

A. 	THIN SECTIO OF AN OOLITE FROM THE LANEY SHALE MEMBER OF THE GREEN 

RIVER FORMATION ON SHELL CREEK, SEC. 9, T. 12 N., R. 98 W., WYO. 

Showiog large oolite grains with eccentric growth zones. The darker granulose parts of t hese grains consis t of mechaoicaUy enmeshed silt, aod the clearer parts consist of fine-grained calciLe partly 

replaced by chalcedonic silica. The groundrnass collSists of chalccdonic silica, with scattered microcrystals of calcite. Eularged ll~ rliameters 

B. SMALL AREA OF THE POLISHED SPECIMEN SHOWN IN PLATE 35 

This shows a part of the oolitic sandstone which contains at a and b fragments of microcrystalline cal­ cite with ferruginous oolite grains suspended in the positions in which they formed, at c and d fragments of algal limestone consisting almost whoUy of Chlorellopsi8, and at e and f unusually large oolite grains that. show the wide concentric banding characteristic of all the oolites in this bed. Enlarged 5 diameters 
ALGAE REEFS AND OOLITES OF THE GREEN RIVER FORMATION 217 

crystalline calcite between the cells of some OhZoreZZopsis colonies are calcite casts of small filaments in 

fascicular groups. These l'esemble somewhat Confervites mantiensis but are not well enough preserved 

to be worth description. 

This reef evidently had four distinct stages of 

growth, the first and third probably by means of 

filamentous algae which left only vague traces of 

themselves. The paucity of small angular grains of 

feldspar and quartz and the absence of limy mudstone in these two zones indicate that they were 

probably fornled in quiet and also clear water. The 

agate-like layers between them are probably of 

inorganic origin, and the abundance of limonite 

grains, secondary after pyrite, suggests that decaying organic matter through its evolution of ammonia 

brought about their precipitation. 

ChZoreZZopsis and probably also some filamentous 

algae fornled the surface layer. During this stage 

the water was apparently more active and deposited 

sonle fine sand in pockets between the algal colonies. 

Small quantities of calcium carb~nate in the form of 

mud were also deposited on and between the colonies 

during their growth. 

The strongly abraded surface of the reef shows 

that after its complete solidification it was subjected 

to a rather potent scouring. It is not clear whether 

during that erosion it was exposed to the weather. 

This reef was found in the lower part of the Tipton' 

tongue of the Green River formation in the NE. 7i 

NE.· 7i sec. 16, T. 24 N., R.' 102 W., Sweetwater 

County, Wyo. 

REEFS LARGELY INORGANIC 

A thin discontinuous reef which is representative of 

a sDlall class of similar deposits that are largely inorganic (see pIs. 34, C; '43, A; 45, A) rests on ostracode 

limestone which contains limestone pebbles as much 

as 1 centimeter in diameter. In places the same bed 

contains small but distinct mud curls. A somewhat 

silnilar pebble conglomerate overlies the reef, but 

in addition to limestone fragments it contains wellrounded quartz, chert, and feldspar pebbles, some 

of which are nearly 1 centinleter in diameter, and 

also larger sharply angular fragments of a similar 

reef. 

The reef itself is about 3 centimeters thick and makes 

an essentially continuous bed. The upper surface 

consists of so~ewhat flattened hemispherical heads 

. of closely spaced wartlike protuberances, which resOlnble in shape, color, and even texture the thickened 

pads on the under side of a cat's paw. (See pI. 43, A.) 

The under surface is flat. 

A polished cross section of the specimen shows that 

it consists of alternating black, dark grayish-buff., 

and light-buff complexly crenulated layers. The 

lowest buff ~yer has a flat base, but on its upper 

sides it bears relatively large, vigorously nodose 

flabellate or in places even arborescent OhZoreZZopsis 

coZoniata colonies between which are pockets filled 

with ostracodes and small angular pebbles of algal 

limestone, all of which are so thickly incrusted with 

lime as to resemble irregular oolite grains. These 

are mi~ed with a little fine sand and cemented by 

clear calcite. Upon these colonies are built the 

hemispherical heads of wartlike protuberances, each 

of which consists of several short cushion-shaped 

buff layers like t1;le basal layer except that they are 

thinner. These are separated by zones of thin dense 

black or gray layers which vary in thickness from 

place to place' but which are continuous across the 

specimen. It is also significant for their proper 

interpretation that in places the black layers line 

cavities, fill cracks, and follow the reentrants below 

overhanging buff layers. (See pI. 45, A.) Moreover, 

their upper surfaces, except where interrupted by 

detrital material, are smooth curves and contrast 

sharply with the richly nodose upper surfaces of the 

buff layers. . 

Between the turbinate or puffball-shaped heads are 

pocket-like depressions filled with detrital nlaterial 

such as small ostracodes, angular fragments of dense 

buff calcite, small sand grains, and oolite grains some 

of which have an ostracode valve for a nucleus. Clear 

calcite fornls the nlatri~ of these pocket fillings. Pyrite 

now partly altered to limonite has completely replaced the fillings of a few such pockets near the top 

of the reef. 

Thin sections of this specimen show that the upper 

part of the basal buff layer and also the other buff 

layers consist of spongy lnicrocrystalline calcite which 

contains a network of algoid lines of coarser-grained 

calcite. They were very probably deposited by a felt 

of algae. (See pI. 34, A.) In thin section it becOlnes 

apparent that the black or dark-gray agate-like layers 

have been completely recrystallized, for their long 

acicular calcite crystals, some of which are more than 

0.1 millimeter long, cross thin layers of yellowish 

organic nlatter and thin zones of lilllonite granules 

that probably mark successive stages of peripheral 

growth. The layers that separate the zones of long 

acicular crystals consist of granular calcite with a 

small quantity of organic matter and an abundance of 

small limonite grains, many of which are cubical. 

Locally the limonite grains are so closely spaced that 

they appear as black bands, even though highly nlagnified. Much of the dark color of these layers is due 

to them. Yet vast nunlbers of irregular black particles, 3 Inicrons or less in dianleter, disseminated 

through the calcite crystals of the\ fibrous layers, also 

contribute to the black or dark-gray tones. 

Apparently this reef grew under variable conditions, 

being built up now by means of algae and again by 

physico-chemical precipitation, and each process was 
218 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1928 

modified somewhat by the sporadic accumulation of 

detrital grains. Moreover, the algal and inorganic 

deposits alternated in a periodic fashion. 

The algal deposits contain pockets and lenses of 

detrital material in which angular lilnestone pebbles 1 

to 3 millilneters in length are fairly plentiful. Therefore it seems probable that the algal layers were fornled 

in shallow water when waves and, currents were more or 

less active. The conditions under which the black 

and gray agate-like layers fonned are not so clear. If 

the black particles disseminated through their crystals 

are organic matter they suggest that, in periods of 

quiet, layers of organic ooze were deposited on the 

algal deposits and that amnlOnia generated by the 

decay of this ooze localized the precipitation of calcium carbonate. This hypothesis is supported to 

some extent by the prevalence in these dark layers of 

cubical limonite grains which are probably secondary 

after pyrite. Then too, in harnlOny with this suggestion there are, in the upper part of the reef, masses 

as much as 1 centimeter in dianleter of pyrite partly 

altered to limonite. Nevertheless, other physicochemical factors probably also operated to precipitate 

calcium carbonate, for ostracode valves and small 

fragments of limestone within this reef are incrusted 

with concentrically layered fibrous calcite tha.t is 

entirely free from iron oxide, organic matter, and 

black particles. 

This reef occurs about 5.5 nleters (18, feet) above 

the base of the Tipton tongue of the Green River 

formation in sec. 21, T. 24 N., R. 101 W., Sweetwater 

County, Wyo. 

REEF FROM THE "MANTI BEDS" 

A reef from the "Manti beds" (pI. 45, B) has the 

form of elongate lenses about 25 centimeters in maximum thickness, rests upon thin-bedded white shaly 

limestone, and is overlain by laminated very limy 

shale. Its upper surface is botryoidal. 

A polished vertical section through the reef shows 

that it is built up of nlany tiers of arched and finelv 

tuberculated layers interspersed with thicker, coarsely 

spongy layers. The thinner layers that resemble agate 

are gently sinuous or arcuate and banded in shades of 

yellowish and brownish gray. Several of the spongy 

zones are minutely punctate. The dark areas shown 

in Plate 45, B, are partly silicified. This reef is unique 

among those of the collection because a small partly 

silicified area of it contains a network of the fossil 

filamen tous alga Confervites mantiensis. (See pI. 33, C.) 

Thin sections of ~he reef show that it consists almost 

wholly of microcrystalline calcite which has a spongy 

structure and is of algal origin. It also contains several colonies of Ohlorellopsis coloniata. Further, some 

of the partly silicified zones consisted originally of 

microcrystalline calcite which shows no structure and 

is perhaps an inorganic deposit. 

This reef is chiefly interesting for its fossil filamentous algae and the numerous coprolites that are associated with them. (See 'pI. 33, B.) It occurs near 

the top of the," Manti beds" in a quarry just east of 

the Mormon temple in Manti, San Pete County" Utah. 

The exact location is unknown, but it is approximately 

sec. 6, T. 18 S., R. 3 E. Salt Lake meridian. 

ALGAL NODULES OR COBBLES 

The algal nodule shown in Plate 46, A, came from 

a layer of silnilar isolated nodules or cobbles between 

two beds of hard gray-green sandy clay. It is irregularly rounded and has a minutely nodose surface. A 

transverse section shows that it is built up of three 

zones of algal deposit about an irregular nucleus of 

dense buff ostracode limestone surrounded by masses 

of closely packed small ostracode shells, which are 

cern en ted in some places by clear secondary calci te 

and in others by gray sandy limestone. 

Under the microscope this specimen shows no fossil 

algae, but nevertheless its microstructure is predominantly algal. The greater part of the first and third 

zones consists of spongy-structured microcrystalline 

calcite in minutely mammillate layers with many small 

pockets of fine-grained, sharply angular sand. The 

intermediate zone consists of a succession of very thin 

and unusually' regular layers. The thicker of these 

consist of spongy microcrystalline calcite with a few 

, pockets of detrital grains and are entirely similar to 

the deposits of the first and third zones of the specimen. 

But the thinner layers consist of radially arranged 

coarse, somewhat elongated crystals of clear calcite. 

Although these layers have obviously been recrystallized and retain no algal structp.re, they are arcuate 

and resemble feltlike colonies of certain filamentous 

algae. Such layers nlay be recrystallized deposits of 

calcium carbonate precipitated rapidly upon the algal 

colonies-for example, by rapid loss of CO2 from the 

surrounding water. But they are considerably different from the fibrous incrustations of acicular crystals 

described on pages 217-218 and also different from the 

concentric layers of oolites and similar thin incrustations upon ostracode shells and detrital grains. They 

are much less uniform, most of them vary rapidly in 

thickness from place to place, and their upper surfaces 

are very irregular and serrate, not smooth like the 

layers in agate structure. Furthermore, their crystals 

are not acicular but blunt, and in many layers the 

individual crystals are not strictly radial, but instead 

groups of them are canted in various directions. For 

such deposits Reis 31 proposed an explanation which 

to ,the writer seems plausible-namely, that for some 

reason the algae died off, and ammonia from their decay 

precipitawd calcium carbonate in the interspaces of 

the spongy mass and at the same time coafsened the 

31 Reis, O. M., Kalkalgen nnd Seesinterkalk aus dem rheinpfalzischen 'rertiiir: 

Geognostische Jahresh., vol. 36, p. 125, 1923. 
ALGAE REEFS AND OOLITES OF THE GREE~ RIVER FORMATION 219 

crystal grain so that the original spongy structure was 

obscured. 

The nucleus of this specin1en was probably a hard 

rnud lUlnp formed close to the place where it was 

found, for its reentrants and salients are all s11100thly 

rounded, and as the cardinal salients are no 1110re blunt 

and rounded than small and protected ones it preslunably had not been rolled 111uch before algae becaIne attached to it. During the first stage of growth 

the nucleus rested upon the base a-b, Plate 46, A. 

Then the nodule was rolled over, and growth occurred 

on less than half its surface, probably because it rested 

against other nodules on the sides c, a, d, or because it 

was partly buried. The third zone of growth apparently formen after the nodule had been again rolled 

over so tha,t it then rested on some part in front or 

behind the plane of the polished face. 

Because these nodules or algal cobbles occur in 

mas~ive st),ndy gray-green clay that is transitional 

between the Tipton tongue of the Green River forn1ation and the Cathedral Bluffs tongue of the 'Vasatch 

fonnation and 1nay be either fluviatile or lacustrine 

and because they contain so much fine sand and have 

obviously been rolled, it seen1S clear that they were 

forn1ed in shallow, son1ewhat active water, perhaps 

near the n10U th of a stream that fed the lake. Although s111aller they are comparable to the layers of 

streanl concretions described by Roddy.32 

These nodules were found in the NE. SE. ~ sec. 

15, T, 25 N., R. 102 'V., Sweetwater County, Wyo. 

ALGAL PEBBLES 

Algae of the Green River formation built not only 

extensive reefs and isolated heads and nodules but 

also rounded pebbles that range from 0.75 millimeter 

to about 5 centimeters in dian1eter. Those that are 

more nearly spherical closely resemble large oolite 

or pisolite grains; the others resemble ordi:t;lary subangular pebbles that have been incrusted 'Yith lime. 

(See pI. 46, B.) Both types and all gradations between 

thenl n1ay occur in the same deposit. Furthermore, 

algal pebbles are aln10st invariably associated with 

true oolite grains, algae reefs or their broken fragn1ents, 

and great quantities of snlalllin1Y ostracode shells. 

N early aU algal pebbles of the Green River formation 

are sn100th, and alth.ough son1e show a marked tendency to exfoliate thin concentric shells that resemble 

egg shells, others are n10re honlOgeneous and are 

weakly pustulose. 

Under the microscope the algal pebbles show structure wholly analogous to that of the larger reefs and 

are clearly distinguishable fron1 the inorganic oolites 

with which they occur. Most of them consist of a . 

spongy aggregate of fine calcite grains that shows no 

fossll algae, but on the other hand son1e consist chiefiy 

83 Hoddy, n. J., COIlcretions in streams formed by the agency of blue-green' algae 

nud related plunts: Am. 1'hllos. Soc. 1'roc., vol. 54, pp. 246-248, 257-258, 1915. 

100874°--29----15 

of layers of Chlorellopsis coloniata. (See pl. 47.) Others 

consist of uniformly microgranular calcite which gives 

no clue to their origin. These can be distingu1shed 

by their shape alone. Although some algal pebbles 

appear to have no nucleus, most of them are built 

around small subangular bits of limestone which were 

probably firm mud when the algae began incrusting 

them; a few contein ostracode shells or inorganic oolite 

grains as nuclei. 

These fossil algal pebbles are closely similar to algal 

pebbles now being formed in some lime-rich freshwater lakes of temperate North America. Those collected by the writer in 1925 from the shore near Squaw 

Island, at the north end of Canandaigua Lake, N. Y., 

range fron1 0.5 to about 2 centimeters in diameter, 

and although they vary greatly in shape, discoid pebbles 

are most plentiful. The outer crust of each pebble is 

hard and fhirly smooth, but the interior is soft and 

exceedingly porous because it consists of minute irregular chalky granules held in a close mesh of dead algal 

filaments that have a vague radial arrangement. If the 

pores of these pebbles were filled with secondary calcite they would be strikingly like many of those from 

the Green River formation. Pollock 33 described the 

formation of similar' algal pebbles in the shallow margins of Ore Lake, Mich. 

Presun1ably the fossil pebbles were formed under 

similar condi tions and in n1uch the same way as the 

recent pebbles which they so much resemble. How­

·ever, locally calcium carbonate seems to have been 

precipitated upon the pebbles without the aid of algae, 

for in some beds not only the pebbles but also groups 

of them and ostracode shells and small mud lumps 

are rather uniformly coated with one or more layers 

of calcite, which has a. distinct fibrous structure with 

the greatly elongated crystals oriented radially. The 

writer regards deposits of this kind as resulting from 

a rapid incrustation due to physico-chemical causes 

identical with those that produce oolites. 

Beds of algal pebbles occur at many places in both 

the Green River Basin of Wyoming and the Uinta 

Basin of Utah and Colorado, but the specin1ens studied 

came froln two localities-one at the base of the 

Tipton tongue of the Green River formation in the 

S'V. 7.:t NE. ~i sec. 27, T. 25 N., R. 103 W., Sweetwater 

County, Wyo., and the other about 161 meters (530 

feet) above the base of the Green River formation in 

sec. 1:1, T. 5 S., -R. 102 W., Colo. 

POSSIBLE ANNUAL LAMINATION OF ALGAL 


DEPOSITS 


Roddy 34 and Schmilde 35 attribute the laJnination 

of certain fresh-water algal deposits to an annual peri33 Pollock, J. D., :Michignn Acad. Sci. Twentieth Ann. Hcpt., p. 249, 1918. 

34 Hoddy, H. J., Concretions in streams formed by the agency of blue-green algae 

and related plants: Am. 1'hilos. Soc. 1'roc., vol. 54, pp. 253-254, 1915. 

36 Schmilde, \V., 1'ostglaziale Ablagerungen im nordwestlichen Dodenseegebiet: 

Neues Jahrb., vol. 11, pp. 114-115, 1910. 
220 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1928 

odicity in the growth of the plants, but each author 

gives a different. cause for the periodicity. Roddy in 

describing algal deposits in a Pennsylvania stream 

says: 

That periodic accretion alternates with a period of quiescence is shown plainly by the concentric laminations of nearly 

uniform thickness. The open porous nature of each lamina 

within and the more solid character without, like the concentric arrangement, is due without doubt to the seasonal conditions of the region. Since algae are essentially thermophilic 

plants, each winter destroys many of them and stops the 

growth of most of the rest, and thus at beginning of the plant 

year (spring) few and widely scattered algae at first produce 

slow and scattered accretion of the limy matter; later the plants 

become more abundant and· by summer they are crowded over 

the surface of each mass. This distribution of the algae seasonally would naturally have its effect upon the structure and 

arrangement of the limy matter, giving a decided though rough 

coralline appearance to the inside portion and a more compact 

texture to the outer part. The theory just given has been 

confirmed by a study of the distribution of the algae on the 

concretionary bodies through the seasons. 

Schmilde, on the other hand, described the lamination of small algal pebbles which are being formed in 

shallow bays of Unter See, Germany, below the outlet 

of the Lake of Constance. Each winter the water 

level is lowered, so that the deposits, unlike those described by Roddy, are left dry for several months, and 

at that time, he says, 

the growth of the algae is interrupted or at any rate greatly 

~t:lstricted, while the life processes go on and therefore also the 

segregation of lime; thus ·it forms a hard, thin limy crust. In 

summer and spring, on the contrary, the plants grow up quickly; 

the precipitated lime therefore accumulates more loosely consolidated and so forms the more porous layers. It seems very 

much to me, therefore, that the zonal structure of the incrustation is correlated with the periodic growth in dry and wet 

habitats; it would be scarcely understandable otherwise that 

an assemblage of algae should be able to show a zonal growth. 

The average annual deposit, which consists of a thin 

dense layer and a soft porous one, ranges in thickness 

from 1 to 2 millimeters. In the deposits described by 

Roddy 36 the annual deposit consists also of a dense 

and a porous layer, but these together range in thickness from 3 to 6 millimeters. 

Not all fresh-water algal deposits, however, are 

laminated. Those in Green Lake, N. Y., studied by 

the writer are not, despite the cold winters of that 

region. Also some reefs in the Green River formation 

are not lanrinated. The presence or absence of distinct lamination in algal deposits might be accounted 

for by a hypothesis that differs slightly from either 

Roddy's or Schmild's-namely, that the thin dense 

layer is due to recrystallization in a thin zone at the 

surface of the deposit. If the ·rate of recrystallization 

is constant .throughout the year or perhaps even lessened during the winter, then it will, nevertheless, have 

a considerably longer time to operate at one horizon 

of the deposit during the winter when the algae are 

86 Roddy, H. J., op. cit., pp. 249-250. 

either d.ead or relatively inactive and consequently 

not adding to the deposit. But several factors might 

operate to counteract the recrystallization during the 

winter. If the rate of recrystallization were slow and 

the algae mildly active, the deposit might grow so 

fast that the effects of recrystallization would be distributed through a thicker zone, as in the summer 

deposit, and so would not be discernible. A nlore 

probable factor, however, might be actual solution of 

the ealciumcarbonate at the surface of the deposit due 

to the greatly increased concentration of the carbon 

dioxide dissolved in the lake water. Chambers 37 and 

Powell 38 have observed that the carbon dioxide and 

bicarbonate content of pond and reservoir waters 

increases noticeably during the winter, owing largely 

to the lessened activity of submerged aquatic plants 

but also to the greater solubility of the carbon dioxide 

in cooler water. This perhaps accounts for the absence of lamination in the reefs from Green Lake, 

N. Y., although, so far as the writer is aware, no analyses or' the water in Green Lake have been made to 

determine the relative quantities of dissolved carbon 

dioxide in summer and winter. Thin dense surface 

zones formed by recrystallization were found only in 

those parts of the algal deposits in Green Lake that 

are buried in limy mud and therefore necessarily 

barren of algae. 

Many but not aIr the algae reefs from the Green 

River formation are distinctly laminated. Those whose 

lamination seems most likely to be annual are the pitted reefs built by OhZoreZZopsis coZoniata Reis. Many 

layers consist of nUlnerous individual algal colonies 

that rise uninterrupted from a common substratum to 

the top of the layer, which is marked by a thin, dense, 

and generally darker-brown layer. These algal layers 

vary greatly in thickness, even within the same reef. 

Of the 56 layers measured the thinnest is 1 millimeter, 

the thickest. about 15 millimeters, and the average 6 

millimeters. Although the writer realizes fully that 

these layers may not be annual and might possibly even 

represent many years, probably ncme of them represent less than one year. Consequently any estimates 

of time based on them ·will err in being too short. 

According to this average rate of accumulation the 

large pitted reef shown in Plate 40, A, which is locally 

as much as 2.1 meters (7 feet) thick, must have required at least 355 years to form. Sernander 39 

"found 	at Benestad, in southern Sweden, varved postglacial algal tufas whose rate of growth is comparable 

to those of the Green River fOl'lnation. The smnmer 

37 Chambers, C. 0., The relation of algae to dissolved oxygen and carbon dioxide, 

with special reference to carbonates: Missouri Bot. Garden Ann. Rept., vol. 23, pp. 

187-192, 1912. 	 ; . 

38 Powell, S. T., The effect of algae on bicarbonates in shallow reservoirs: Am. 

Waterworks Assoc. Jour., vol. 2. pp. 703-708,1915. 

39 Sernander, Rutger, Exkursions fUrher fUr Sklme: Vierte Internat. Pflanzengeog. 

Exkursion durch Skandnavien, 1925; cited by Antevs, Ernst, Varved sediments, 

in Twenhofel, W. H., and others, Researches in sedimentation in 1925-26, p. 83, 

National Research Council, 1926. 
ALGAE REEFS Al\T]) OOLITES OF THE GREEN RIVER FORMATION 221 

la~'TS nre ,mOOS-e" ruld the autunm layers, which contain 

leaf iimlPressi({))n:s., are thin and hard. A bed of that 

tufa lI. ..:8D, mreibeT.s thick had 420 varves, which averaged 

4 milljJnette:r.s ,m thickness. 

The pittterll. Ohlorellopsis reefs are more coarsely laminated !illDllm '1hlrence presumably grew more rapidly than 

the othlCT meefs of the Green River formation, but a 

d.iroct ((.'(Q)n'la»:arison of the rates can not be made because 

the ti1l1le \V,a!iue of the laminae in the other reefs is far 

too tUlID.iC.'<CTtnin. 

OOLITES 

In :mm. (e:rurlier paper 40 the writer stated his belief th'at 

the oolites so intimately associated with the algae reefs 

in :nI())Titlhtern Sweetwater County, Wyo., were formed 

. by :aTI,g:ae or bacteria. In this more critical study of 

sevclrru :specimens of oolites froom various parts of the 

Groen River fOrJllation the writer not only found no 

reason It,(J) ,postulate a genetic relation between bact.eria :mad the oolites but also was unable to find any 

condlllsi·~..r(e (evidence to support the hypothesis that they 

were iOlI'med by algae. On the contrary, it can be 

clearly dl{,)lnlonstrated that the oolites of a few beds are 

of inoIg:runi,e origin. One of these beds consists almost 

wholly of a gently cross-bedded mixture of small oolite 

grains and fine grains of quartz and feldspar, but it 

nlso contains several small fiat mud lumps and mud 

curls. Sonie of the smaller lumps consist of calcite 

that is nearly cryptocrystalline. These contain a few 

oolite grains that do not touch and in general are 

widely spaced. Clearly they were suspended in the 

matrix when it was an ooze. (See pI. 48, B.) The 

oolite grnins thelllselves have no fibrous or radial 

structure but are exceedingly fine grained and indisguishable frOln the mu,trix except for their perfect 

tholwh rather wide concentric banding and noticeably

dark~r color. They are dark yellowish brown, ~hereas the Inatrix is pale brownish gray. Evidently the color 

is due to iron, because the weathered oolite grains are 

coated with limonite. Moreover, the iron is clearly 

concentrated in them with respect to the matrix. 

Nuclei are rare, but some of the oolite grains contain 

minute quartz or feldspar grains at their centers. 

Apparently these oolites in the dense matrix were 

fOl'lned in a similar lllanner to that elucidated by 

Schade:1l The original ooze or gel in which the oolite 

grains fOl'llled consisted of colloidal ferric hydroxide 

with a large adlllixture of extremely finely divided 

calcimll carbonate. From the facts that the calcite 

crystals in the oolites and nlatrix are now only 1 to 

2.5 m.icrons in dialneter and that some crystal growth 

has probably occurred since the Eocene it is possible 

that the CalCiUlll carbonate luay also have been in a 

40 Dl'l1dley, W', H" Shore phases or the Green River formation in northern Sweet· 

watCl' County, Wyo.; U. S. Oeol. Survey Prof. Paper 140, p. 126, 1926. 

41 Sehode, Heinrich, Zur Entstehung del' lIal'llsteine und !lhnlicher konzentrisch 

gcschlchtetcr Steine orgauischen und onorgonischen Ursprungs: Zeitschr. Chemie 

u.lndustrio del' KoJloide, vol. 4, p. 265, 1909. 

colloidal state, though that would not have been 

necessary for the formation of oolites. Growth of the 

calcite crystals was perhaps inhibited by the protective action of the colloidal ferric hydroA;de. Moreover, the complete absence of long acicular crystals 

forming radial structure strengthens this possibility, 

especially because the calcium carbonate or crystalloid 

component'waRlarge. ! The ferric hydroxide must have 

been coagulated by negati ve ions such as carbonate or 

chloride in the solution, and then because the minute 

coagulated particles are unstable in the presence of 

larger ones, and apparently also in the presence of any 

larger foreign particle such as a quartz or feldspar 

grain, they coalesced into spheres, mechanically enmeshinO' a considerable quantity of the suspended cal- b • • 

cium carbonate. By that process the oolIte graIns, 

grew. Apparently their growth was ljmited by the 

supply of ferric hydroxide, as they seem to have fLbstracted the greater part of it from the matri~. 

Their concentric lamination, as Schade's experiments 42; 

indicate, is a characteristic property of coagulated colloids that contain admixtures of foreign material and 

depends upon slight changes in the proportions of the 

constituents, upon concentration of the salt solution, 

and consequently also upon the rate of coagulation of 

the colloidal component and the viscosity of the fluid 

or gel. 

Now, because all the isolated oolite grains, which 

made up a considerable part of the whole bed, nre 

precisely identical with 'those in the small pieces of 

dense matrix it seems probable that they were also 

formed in the same way and, moreover, in the snnle 

medium or matrix, but that the nlatrix was washed 

away from them when the bottom deposits at that 

place were reworked by waves or currents. Only those 

parts of the matrix that were partly solidified, perhaps 

by incipient recrystallization after the abstraction of 

the ferric hydroxide to form the oolites, or perhaps 

only bound by some of the residual eolloidal matter, 

were able to withstand the disturbance and thus f01'111 

the small lumps containing the oolite grains still suspended a-s,they were formed. 

Both Bucher 43 and Twenhofel 44 state that for 

oolites to be formed through the change of at least one 

component from a colloidal to a solid state it is necessary that the oolite grains should grow suspended in 

an ooze or a jelly-like medium. Obviously some and 

perhaps most oolites are formed while suspended in 

gel or ooze, but is that a necessary factor? Schade's 

experiments 45 seem to indicate that it is not, for he 

states that only an imperceptible quantity of the 

colloidal component relative to the crystalloid pre­

., Idem, pp. 262-264. 

4S Bucher, W. H:, On oolites and spherulites: Jour. Oeology, vol. 26, p. 603, 1918. 

4j Twenhorel, W. H., Treatise on sedimentation, p. 543,1926. 

.~ Schade, Heinrich, Zur Entstehung der Harnsteine und !lhnlicher konzentrisch 

geschichteter Steine organischen und anorganischen Ursprungs: Zeitschr. Chemie 

u. Industrie der Kolloide, vol. 4, p. 263, 1909. 
222 "SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1928 

cipitate is necessary for the successful formation of 

artificial gallstones. Moreover, those gallstones, which 

are oolites, are formed in a mobile liquid and are not 

suspended in a gel. Furthermore, as natural gallstones 

are formed their liquid medium is almost continuously 

in motion. So also the oolites that were formed in the 

hot-water coil of a furnace as described by Twenhofel 46 

must have been alternately at rest and in nlotion in a 

liquid far too fluid to hold them in suspension. 

Furthermore, the vegetable pearls formed in the 

interior of a coconut as mentioned in another paper by 

Schade 47 probably rested on the bottom of the coconut 

and were occasionally moved. about. These so-called 

pearls consist of CaC03 with a nitrogenous organic 

substance as the binding colloid. All that appears to 

be requisite for the formation of the oolites in Schade's 

experiments 48 was the coagulation of a very small 

amount of a colloidal substance with which may be 

admixed, in almost any proportions, one or mOre other 

components. In gallstones the other component is a 

crystalloid which precipitates out of a salt solution. 

Now Schade 49 further points out that the tendency of 

the minute droplf(ts or globulites of coagulated fibrin 

to coalesce and form larger droplike particles with a 

, netlike structure of intersecting needles thickened at 

their intersections and the subsequent shrinkage of the 

mass are not peculiar to fibrin but are common to 

other colloids. 

Empirically, therefore, it seems wholly possible 

that calcareous oolites might be formed in natural 

environments that were quite as fluid as the media 

in which natural and artificial gallstones are formed. 

Lake water might be saturated with calcium carbonate and contain a colloidal component such as 

ferric hydroxide, silica, algal gelatine, '01' some of the 

products of deconlPosing organic nlatter so dispersed that it would not increase the viscosity of 

the solution enough to hold nuclei and small oolite 

grains suspended. Such conditions where the growing 

oolites rest one against the next or are only partly 

suspended in silty mud and are occasionally moved 

by storms seem to the writer better adapted to the 

fonnation of many of the oolites in the Green River 

formation, especially those larger than 1 millimeter 

in diameter, 'for they are unsynlmetrical, are of various sizes, and show two or nlore zones of concentric 

growth that are eccentric ,vith respect to one another and in some also to the nucleus. (See pI. 48, 

A.) Moreover, many of them contain layers in which 

clay and silt are generously admixed with the microcrystalline calcite. 

46 Twenhofel,. W. II., Treatise on sedimentation, p. 540, 1926. 

H Schade, Heinrich, Uber Konkrementt'i1dungen beim Vorgang der tropfigen 

Entmischung von Emulsions-kolloiden: Kolloidchemische Beihefte, Band 1, pp. 

375-390, 1910. 

48 Schade, Heinrich, Zur Entstehung der Harnsteine und !thnlicher konzentrisch 

geschichteter Stcine organischen und anorganischen Ursprungs: Zeitschr. Chemie 

u. Industrie der Kolloide, vol. 4, p. 263, 1909. 


49 Idem, p. 178. 


Conditions in Pyramid Lake,. N-ev., per1;laps 

approaching these have been described by Jones.50 

When the lake is clear and qruet the oolites, which 

are not suspended but rest against each other on the 

bottom, grow by the formation of minute aragonite 

needles that are radially oriented, but when the 

bottom is stirred up by storms the silt that is thrown 

into suspension is admixed with the aragonite, and 

granular stony layers. that are concentric with those 

layers having radial fibrous structure al:e fonned. 

In Pyramid Lake, however, . the calcium carbonate 

is. being precipitated from warm spring water, and so 

the conditions' are somewhat different from those 

that must have prevailed in the ancient Green River 

lakes, where the beds of oolite are many square Illiles 

in area and an origin by warm springs is ahnost 

surely precluded. Yet probably the means by which 

the components are precipitated has little general 

effect upon the growth of the oolite grains, provided 

the material is in the proper state.· Thus the precipitation of calcium carbonate from lake water by 

a change in temperature or by the gradual abstraction of carbon dioxide from the bicarbonates in solution by the growth of submergea aquatic plants, 

as describedI by Hassack,51 Chambers,52 and Powell,53 

together with the simultaneous coagulation of even 

a very small amount of a suitable binding colloid, 

might conceivably produce oolites over large areas 

of the lake bottom, even though the bottonl was 

sandy or silty and the growing oolite grains were 

not suspended. Soft ooze bottoms would of course 

provide a medium in which oolite grains, at least 

while small, would be more or less completely suspended. Such an ooze' might not necessarily contribute to' the growth of the oolite grains except in 

so f~r as it was mechanically enmeshed. 

SUMMARY 

Certain but not all chlorophyll-bearing algae precipitate 'calcium carbonate from natural waters by 

their photosynthesis, a process by which they abstract 

not only the carbon dioxide that is dissolved in water 

but also that held in solution as bicarbonates. This 

process has for a long time been clearly established by 

laboratory experi~entation and observation of algae 

in natural habitats. As this process depends directly 

upon sunlight it follows that the algae reefs in the 

Green River formation must have been produced in 

shallow water that was relatively clear, at least for the 

50 Jones, J. c., Quaternary climates; Geologic history of Lake Lahontan: Carnegie Inst. Washington Pub. 352, pp. 14-18,1925. 

61 Hassack, Carl, Uber das Verh1iltnis von Pflanzen zu Bicarbonaten und fiber 

Kalkincrustation: Untersuchungen aus dem Bot. Inst. Tfibingen, vol. 2, pp. 

467-473,1888. 

62 Chambers, C. 0., The relation of algae to dissolved oxygen and carbon dioxide 

with special reference to carbonates: l'dissouri Bot. Garden Ann. Rept., vol. 23, 

pp. 178-204, 1912. 

~3 Powell, S. T., The effect of algae on bicarbonates in shallow reservoirs: Am. 

Waterworks Assoc. Jour., vol. 2, pp. i03-i08, 1915. 
ALGAE REEFS AND OOLITES OF THE GREEN RIVER F9RMATION 223 

greater part of the time. These two factors, however, 

are plainly interdependent, the depth at which the 

algae reefs could be fonned varying directly as the 

clarity, or, stated better, inversely as the turbidity, 

which is the principal factor limiting light penetration 

in fresh water.54 The depth may have been as much 

as 4.5 Jneters (15 feet),' or perhaps even more, but 

probably 1110St of the reefs and certainly sonle of them 

were formed in water less than 1.8 nleters (6 feet) 

deep. One reef at least was formed in very shallow 

water, for it contains the molds of emergent plant 

stems in the position in which they grew. 

In order that the limestone precipitated by the algae 

could persist, as Johnston and 'V"illiamson 55 have 

pointed out for linlestone in general, the water surrounding thCln nlust have been saturated with respect 

to the normal carbonate of calcium. From this it 

follows that lime was continually being brought into 

the lake and that the water circulated, even though 

perhaps slowly, and thus replenished the lilne precipitated by the algae. Rather vigorous circulation 

of the water around lnany of the reefs and beds of 

algal nodules and pebbles is, however, revealed by 

fragments of algal deposits, lilny lnud lumps, and 

transported sand and oolite grains either within the 

reefs or very intill1ately associated with them. Indeed 

pebbles as much as 1 centinleter in diameter are associa ted wi th one reef. 

Algae reefs are most plentiful in shore phases of 

the Green River formation, where they are irregularly 

distributed through the entire thickness of the formation, but elsewhere they are confined almost wholly 

to the basal Illember, whose lithology is similar to 

that of the shore phases. At a few localities remote 

from shore phases, where those parts of the formation 

between the basal member and the lowest oil-shale 

zone and between the uppermost oil-shale zone and the 

top of the formation consist of hard limy or silty shale, 

there are a few thin algae reefs. 

The reefs are nowhere closely associated with oil 

shale even of very low grade. Their absence from 

those parts of the formation that consist predominantlyof oil shale is clearly due to the fact ·that the 

conditions necessary to the fonnation of oil shale are 

distinctly unfavorable to the formation of algae reefs. 

Where oil shale was formed stagnation of the water 

and putrefaction of great quantities of org~nic ~atter 

effectively inhibited the growth of algae, which were 

the I110St active reef builders. Furthermore, in those 

parts of the lake where decaying organic ooze was 

abundant the ammonia generated by the decay 

quickly precipitated the calcium carbonate, which in 

turn was buried in the ooze or formed thin layers 

upon it. 

61 Fore!. F. A., Lo Leman, vol. 2, pp. 426-427,1895. 

M Johnston, John, and Williamson, E. D., The role oC inorganic agencies in the 

deposition of calcium carbonate: Jour. Geology, vol. 24, p. 735, 1916. 

The scarcity of algae r~efs in the uppermost member of the formation, even in deposits that were 

clearly laid down in shallow water, may be ascribed 

to one or more of three causes-(l) the increased concentration of sulphates in the lake, which at one stage 

became so great that a large quantity of glauberite 

crystallized out in the mud; (2) a lessened quantity of 

lime in solution available for the formation of algae 

reefs, either because lime was less soluble in the more 

saline lake water or because the supply brought to the 

lake was diminished; (3) periodic evaporation of the 

lake during the normal growing season of the algae. 

From the distribution of the algae reefs, their bedlike shape, and their evident origin in very shallow 

water, the writer concludes that the shore phases of 

the Green River formation, some of which are as much 

as 40 kilometers (25 Illiles) wide, and also much of the 

whole basal member were deposited in water not more 

than 15 feet deep. The floors of the two great Eocene 

lakes, even from the beginning, were very smooth and 

had only gentle basinward slopes, for the original surface that each lake flooded was a nearly level plain of 

fluviatile aggradation, Il1arking the top of the Wasatch 

formation. The wide lateral distribution of suncracked bedding planes and of mud curls at many 

horizons in the lacustrine deposits, moreoyer, indicates 

that during the greater part of their existence the 

. lakes had nearly level bottonls. 

The basal member of the Green River formation 

contains more algae reefs in the vicinity of the Douglas 

Creek anticline than on either side of it. From this 

the writer concludes that the lake was shallower there, 

although it is in the central part of the basin. 

Algae reefs in parts of the "formation above the basal 

member and remote fr01n the shore phases represent 

a reversion of the ecologic conditions to those which 

prevailed at earlier stages of the lakes.. Reefs in the 

"upper parts of shore phases that are contemporaneous 

with the saline stages of the lakes were very probably 

formed close to the Illouths of streams or perhaps in 

small, somewhat isolated basins fed by streams or 

fresh springs. 

The abrupt change in lithology between the basal 

Inember and the upper part and the absence or scarcity 

of algae reefs from the upper part indicate a decided 

change in the ecology of the lakes, but a discussion of 

that subject is not gennane to this report. 

According to the writer's interpretation of the origin 

of calcareous oolites and of fresh-water algae reefs 

oolites may be intimately associated with algae reefs 

because the conditions favorable to the formation of 

oolites are in general also favorable to the growth of 

algal limestone deposits, though the converse is by no 

means true; or they may be intimately associated 

because the oolite grains were transported to the 

growing reef in the same way that clastic grains are 

carried to and inclosed in algae reefs.