80 EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



EEVIEW OP THE PALEOZOIC GEOUPS DIEEOTLY EAST OP THE WIND 



EIVEE EANGE. 



Altlioiigli the series of palgeozoic formations east of the range is incom- 

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

 members, and by the uniformity mth 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 group : 

 Eed and yellow sandstones and shales near base. Tliin banks of dolomite in 

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

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

 Thinning out toward the north. 

 Thickness 250 feet. 



Carhoniferoiis grottp : 

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

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

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

 cified) : Productus, Orthis, Crinoids, Orthoccras, Spirifer, Sjnrigera, and others. 

 Thickness 2^000 to 2,200 feet. 



Sudcarhoniferons group : 

 Dolomites and dolomiifcic limestones near base. Calcareous sandstones and 

 some yellow and brownish shales iuterstratified. 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) : Spmfcr, 

 OrtUs, 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. Iuterstratified 

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

 TJieca (f), Corals, and others. (Gradually pinching 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. Eests 

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

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



Total thickness of palseozoic formations east of Wind Eiver Eange.. 3,350 to 3,750 feet. 



MESOZOIC FOEMATIOKS. 



TELiS. 



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

 extensive series of " Eed Beds " as Triassic. Thus far no palaeontological 

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

 Kthological character of the series, w^e find that it closely corresponds 

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

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

 sixths of its vertical dimension. As we caimot, however, utihze such 

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

 forced to regard the definite geological i3osition of the Eed 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 chajige them. 

 A large pro]3ortion of the fossils that might be expected to occur in the 

 Eed 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. 



