Ifayden.] 470 ^^*^^' '' 



of older date are seen, while on the west side, abont five miles 

 distant in a straight line, the entire series from the Carboniferous 

 to the summit of No. 3 Cretaceous are visible, inclining at greater 

 or less angles from the slope. The nucleus of the mountains is 

 sienite of various degrees of fineness and compactness, inclining 

 from 50° to 70° towards the soutli-east or nearly east. 



It is an important question to determine the exact relation of 

 these metamorphic rocks, which form the central portion of all 

 tlie mountain ranges, to the unchanged beds which usually in- 

 cline from their sides. Do they conform to each other or not ? 

 Did the metamorphic rocks lie in a more or less inclined position 

 prior to the deposition of the Silurian or Carboniferous beds 

 upon them? We have thus far found it difficult to determine the 

 conformability or nonconformability west of the Laramie range ; 

 but on the east side of the mountains, especially near Fort La- 

 ramie and along the eastern slope of the Big Horn and Wind 

 River Mountains, the discordant relation of the two series of 

 rocks is very apparent. These questions will have a most im- 

 portant bearing when we attempt to reconstruct the history of 

 the physical revolutions which have occurred in the West during 

 past geological epochs. The sienite beds which form the nucleus 

 of the small range of mountains between the Big and Little La- 

 ramie Rivers inclining eastward, were pushed up in such a way 

 that the east front is almost vertical, and the Cretaceous beds at 

 the base, which must have been borne upward in part during 

 the elevation, have fallen abruptly down, so that in some in- 

 stances they have passed the vertical position 20° to 30°. East 

 of the Big Laramie and all along the western slope of the Lara- 

 mie range, the entire series of unchanged rocks are visible, incli- 

 ning at moderate angles from the mountain sides. On the west 

 of this I'ange the slope is more gentle, and the Carboniferous, 

 Triassic and Jurassic and Cretaceous beds present their upturn- 

 ed edges clearly to the scrutiny of the geologist. The synclinal 

 valley here through which the Little Laramie flows is about five 

 miles wide, and crossing this stream west we find the full series 

 inclining from the mountain slope eastward. The dip of the red 

 beds is from 40° to 60°, that of the Cretaceous 40°. 



No fossils have been found in any of the unchanged rocks 

 below No. 3 Cretaceous west of Fort Sanders, nor does the na- 

 ture of the beds indicate that the physical conditions during their 

 their deposition were favorable for the existence of animal or 

 vegetable life, certainly not for the preservation of its remains. 



