ANOTHER LOCALITY OF EOCENE GLACIATION IN 

 SOUTHERN COLORADO 1 



WALLACE W. ATWOOD 



Harvard University, Cambridge, Massachusetts 



Since the publication of the paper on the Eocene glaciation 

 recorded at the northwest base of the San Juan Mountains near the 

 village of Ridgway, 2 the author's attention has been called to a 

 similar discovery made by Mr. Charles W. Drysdale in British 

 Columbia at about the same time. 3 



When Eocene till was found near Ridgway, and the formation 

 was given the name Ridgway till, it was anticipated that other 

 glacial deposits of the same age would soon be recognized in other 

 parts of the Rocky Mountain province. Each of the larger ranges 

 in this great geographic province has had a history somewhat 

 similar to that of the San Juan Mountains. These ranges were 

 all uplifted, some as great anticlinal arches, some as domes, and 

 others with some faulting and intrusion, at the close of the Meso- 

 zoic era or. beginning of the Cenozoic time. Those great arches 

 and domes were dissected into mountain forms, and, when favorable 

 climatic conditions prevailed, glaciers probably formed in many 

 of the higher basins among those mountains and assisted in the 

 further dissection of the ranges. Now that Eocene till has been 

 discovered in British Columbia, and at a locality to be herein 

 described near the south margin of the San Juan Mountains, it 

 appears to be well established that conditions favorable for the 

 formation of Alpine glaciers did obtain in the western portion of 

 North America during early Tertiary time. 



1 Published with the permission of the Director of the United States Geological 

 Survey. 



2 W. W. Atwood, "Eocene Glacial Deposits in Southwestern Colorado," U.S. 

 Geol. Survey, Prof. Paper 95-B, 191 5. 



J C. W. Drysdale, "Geology of Franklin Mining Camp, British Columbia," 

 Canadian Geol. Survey Mem. 56, 1915. 



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