HOLMES.] BEAR RIVER MOUNTAINS. 195 



flow may have had its source far to the east. There seems at least to 

 be no evidence of vertical flow or intrusions in the western portions of 

 these mountains. The trachyte is uniformly gray and compact, and, 

 where rising above timber-line, weathers into the usual gothic forms. 



The streams which head about the summits descend in all cases 

 through the Cretaceous shales, and at the immediate bases of the mount- 

 ains reach and penetrate the hard sandstones of the Lower Cretaceous, 

 and thus the canons, which can be traced by the eye far out into the 

 surrounding plains and plateaus, have their beginning. To the eye, a 

 more lovely region than that about these mountains cannot be found. 

 The steeper slopes are covered by a dense growth of pine forest, and 

 the gentler slopes below by fine aspen forests, interspersed with many 

 park-like openings in which grass and flowers grow luxuriantly. 



BEAK EIVER MOUNTAINS. 



South of the San Miguel Mountains, and on the divide between the 

 east and west branches of the Dolores, there is a group of low mount- 

 ains or hills in which there has been considerable disturbance of the 

 strata. A number of the higher points are capped by trachyte and 

 penetrated by dikes. Strictly speaking, this little range is but a frag- 

 ment of the great mountain system to the east, from which it has been 

 severed by the great valley of the South Dolores or Bear River. In 

 1875 Dr. Endlich examined the high region to the east and found it to 

 be chiefly Carboniferous. He failed to recognize the Jurassic and Trias- 

 sic formations, and therefore makes the Lower Cretaceous strata rest 

 upon the Carboniferous. Although I cannot be positive on this point, 

 I feel confident that strata representing these ages occur all along the 

 cafion of Bear Eiver, and extend to the summits of the Bear River 

 Mountains, although they are certainly neither equal in thickness to 

 nor so characteristically marked as in the canons farther south and 

 west. 



On the south, west, and north the Mesozoic rocks rise to the summits 

 of the Bear River Mountains; on the south and west they soon sink 

 beneath the floor of the great plain, and to the north pass by a gentle 

 dip beneath the San Miguel Mountains. 



The eastern portions of the group seem to be composed of Carbonif 

 erous rocks, at least 2,000 feet of which are exposed between the sum 

 mits and the bed of Bear River. 



