80 REPORT UNITED STATES GEOLOGICAL SURVEY. 



REVIEW OF TIIE PALAEOZOIC GROUPS DIRECTLY EAST OF THE WIND 



RrVER RANGE. 



Although the series of palaeozoic formations east of the range is incom- 

 plete, it is rendered very interesting by the regular superposition of its 

 members, and by the uniformity with which the different groups partici- 

 pate in the effects produced by dynamical disturbances. A table, indi- 

 cating the succession of strata, is here produced, which may facilitate 

 the comparison of this region with others : 



Permian (/roup : 

 Red and yellow sandstones and shales near base. Thin banks of dolomite in 

 the shales. Yellow sandstones, partly qnartzitic and gray, yellow, and pink 

 shales higher up. Sandstones of lighter shades and some gypsum near top. 

 Thinning out toward the north. 

 Thickness .250 feet. 



Carboniferous group : 

 Massive beds of blue, partly crystalline limestones. Near base magnesian 

 limestones interstratified with the others. Concretions, nodules, and small 

 veins of several varieties of quartz traversing the entire mass. Fossils (sili- 

 ciiied) : Productus, Orthis, Crinoids, Orthoceras, Spirifer, Spirigera, and others. 

 Thickness 2,000 to 2,200 feet. 



Suhcarboniferous {/roup : 

 Dolomites and dolomitic limestones near base. Calcareous sandstones and 

 some yellow and brownish shales interstratified. General color of the rocks 

 yellow and gray. Some of the strata blue. Concretions of quartz not so 

 frequent as in the preceding group. Fossils (mostly silicified) : Spirifer, 

 Orthis, Crinoids, Corals, Orthoceras, Productus, Chonetes, Spiriferina, and 

 others. 

 Thickness 600 to 7 00 feet 



Calciferous group : 

 Blue and whitish limestones and dolomites. Oolitic in part. Interstratified 

 with some thinly-banded shales. Fossils: Orthistritonia, DiceUocephalus, 

 Theca (?). Corals, and others. (Gradually pi 'hing out to the southward.) 

 Thickness 220-280 feet. 



Potsdam group : 



Massive and thin beds of quartzite. Color varies from bright red to deep rusty 

 brown. Narrow interstrata of dark brown metamorphosed shales. Rests 

 directly on the granites. Junction-line often obscured on account of meta- 

 morphism. Fossils : Lingula, Obolus, Obolella, Thickness 280 to 320 feet. 



Total thickness of palaeozoic formations east of Wind River Range.. 3,350 to 3,750 feet. 



MESOZOIO FORMATIONS. 



TRIAS. 



In Colorado and at other localities we are accustomed to regard the 

 extensive series of " Bed Beds" as Triassic. Thus far no palseontological 

 evidence has been adduced in direct support of this view. Examining the 

 lith ©logical character of the series, we find that it closely corresponds 

 with that exhibited by the Keuper of the European trias. This latter, 

 similar to our Eed Beds, is totally devoid of fossils through about five- 

 sixths of its vertical dimension. As we cannot, however, utilize such 

 similarities for the purposes of establishing identity of formation, we are 

 forced to regard the definite geological position of the Bed Beds as 

 unsettled. With this proviso, we shall speak of " Triassic" strata in this 

 report. Subsequent investigations may produce material which will 

 confirm the views provisionally held, or they may radically change them. 

 A large proportion of the fossils that might be expected to occur in the 

 Bed Beds, will probably prove, if found, either to offer but little infor- 

 mation or to simply afford ample material for discussion as to their cor- 

 rect interpretation. 



