228 GEOLOGICAL SURVEY OF THE TERRITORIES. 



tion. It seems incredible that a stream should have been able to erode 

 a canon more than 1,000 feet in depth, when the distance from its source 

 to the point of observation is but five miles, and it furthermore seems ex- 

 tremely improbable that such erosion should have progressed and the 

 walls of the canon have remained as steep as they are at present. I am 

 not prepared to defend any view on the subject at present, but it seems 

 to me that an effect produced either by volcanic or plutonic earthquakes 

 might have the same result. 



About four miles below San Miguel Lake, the Lower Cretaceous sand- 

 stones set in in the canon, and continue from there as far as it was sur- 

 veyed. Crossing the divide from the San Miguel to Eio Dolores, the gray 

 shales are traversed. At that locality they dip off to the west. Tbe un- 

 conformability between them and the red sandstones of Carboniferous age, 

 has been mentioned in the chapter on Carboniferous. From Mount 

 Wilson the volcanic material has flown eastward, and covered a con- 

 siderable portion of the gray shales ; at the junction they are somewhat 

 metamorphosed, but not to the extent observed in the region of Mount 

 Sneffels. To the south of Mount Wilson No. 1 again crops out, in the 

 canon of the Dolores ; along a number of the high ridges south of the 

 river the characteristic white sandstones are found overlying the red 

 sandstones, covered in turn by volcanic rocks. 



From the position the Cretaceous beds along the San Miguel and Eio 

 Dolores occupy, it is evident that they have been deposited at a time 

 long after the upheaval that caused the formation of the main anti- 

 clinal axis above mentioned ; and furthermore, it is very probable that a 

 considerable amount of time elapsed between the two epochs. 



