MEDICINE BOW RANGE. Ill 



of fine-grained dark diorites, some of which have been described as occur- 

 ring in the great white quartzite formation of the Medicine Peak group. 



Volcanic rocks of Tertiaiy age were not observed, and probably do 

 not occur within the Archaean belt. They do, however, occur, as pre- 

 viously mentioned, along the flanks of the range, on the east side of the 

 North Park, where great flows of rhyolite have poured down from Mount 

 Richthofen. Some details in regard to them will be found in the descrip- 

 tion of the North Park. 



