peale.] GEOLOGY GREEN RIVER BEDS. 159 



The beds given in the lower part of the section are probably of the 

 same horizon as the Green Eiver group, as I have shown in the table, 

 while those above represent the Biidger group. It is impossible at 

 present to tell any more definitely the line that separates them. 



The following is the description given by Dr. Hayden* of the Green 

 Eiver group, as exposed in the valley of Green Eiver : " The laminated 

 calcareous shales gradually pass down into yellow-gray and brown in- 

 durated clays, sands, and sandstones, until the well-defined coal-strata 

 are exposed without the least appearance of discordancy." In other 

 portions of the report for 1870, he gives descriptions of the Green Eiver 

 group, and speaks of their being worn into towers and other picturesque 

 forms. Prof. Theo. B. Comstockt gives the following description: 

 " The Green Eiver beds are mainly composed of a series of shales, marls, 

 and harder calcareous strata." . " The texture of the different beds is 

 quite variable, but in general the streams which have cut their chan- 

 nels through them are walled by nearly vertical cliffs, and the buttes 

 and benches for the most part have quite precipitous sides. Numerous 

 joints occur in many of the strata, particularly in the more compact 

 kinds, and fine examples of concretionary structure or weathering are 

 not rare. The tendency of the thick beds of marly sandstone on the 

 banks of Green Eiver, at the crossing, to weather spheroidally is very 

 noticeable, and this is repeated in various degrees in the argillaceous and 

 calcareous rocks as well." In regard to the Bridger group he says,| " The 

 beds of the Bridger group, as a whole, are readily distinguishable from 

 those of the Green Eiver group, being mainly composed of dull-colored 

 indurated clays and arenaceous layers of considerable thickness, the 

 latter usually brownish, or dull yellow or gray, often with more or less of a 

 concretionary structure." Dr. Hayden (see Eeport of 1870) gives the 

 same general description. I have quoted these descriptions to show the 

 resemblance of the strata given in the section made on Plateau Creek to 

 the strata found farther north. A comparison shows the same general 

 characters, even to the spheroidal weathering of some of the layers. 

 Although the beds included under layer No. 57 of the section correspond 

 to the description quoted above of the Bridger group, their identity is 

 by no means certain. Another season 1 hope to obtain more evidence 

 on the question. These beds form the cliffs immediately beneath the 

 plateau of station 48, and are prominent from a great distance, on 

 account of their white color. They also outcrop in the cliffs on the 

 north side of the Grand opposite the plateau and extend far to the north- 

 ward. They are also seen far to the westward and south westward, be- 

 tween the Colorado and Little Colorado or Chiquito Eivers. In this 

 region they are thus referred to by Professor Newberry :§ " Some miles 

 north of camp 96 (situated about latitude 36°, longitude 110° 45') a mesa 

 wall rises to a height which we estimated at something like twelve 

 hundred feet. It occupies 30° of the horizon in that direction, and shows 

 bold, nearly perpendicular faces both in profile and in front. These are 

 pure white in color and reflect the sunlight like sun." "Eising,as it does, 

 so distinctly from the mesa of Lower Cretaceous, but two formations are 

 left in the series of which it could be composed, Upper Cretaceous and 

 Tertiary." These bluffs are probably a portion of the same strata that 

 form the bluffs on the Grand and beneath the plateau of station 48. 

 Professor Newberry did not have an opportunity to examine them, but 



* Report U. S. Geol. Survey, 1870, page 71. 



t Report upon Reconnaissance of Northwestern Wyoming, 1873, pages 123, 124. 

 i Report upon Reconnaissance of Northwestern Wyoming, 1873, page 127. 

 § Ives's Colorado Exploring Expedition, Geological Report, page 87. 



