732 ABSTRACTS OF PAPERS 



EVIDENCE OF THREE DISTINCT GLACIAL EPOCHS IX TEE SAS JUAX 

 MOUNTAINS OF COLORADO 



BY WALLACE W. ATWOOD AND KIRTLEY F. MATHER 



(Ahstraet) 



Abundant evidence of two distinct Glacial eix)chs bas been reported by 

 several investigators from various mountain ranges in the western ix)rtion of 

 the continent. During tbe past season glacial deposits have been examined and 

 mapped about tbe margin of tbe San Juan Mountains, wbicb deposits bave been 

 intei-preted to indicate an epoch of glaciation distinct from the two later 

 epochs that have been clearly recognized in the history of the range. 



For convenience, the three distinct epochs are referred to, beginning with the 

 oldest, as "San Juan," "Big Horn," and "Uinta." 



The composition, distribution, and topograpliic relations of the San Juan 

 glacial drift indicate that this earliest known epoch was separated from the 

 Big Horn Glacial epoch by a much longer time than the Big Horn was sepa- 

 rated from the Uinta. The two later eiwchs appear to have been separated by 

 a much longer time than has elapsed since the last disappearance of glacial ice 

 from the range. The San Juan Glacial epoch is so far removed from the 

 present time that the glacial deposits of that eix)ch are found at but a few 

 places, where conditions were most favorable for their preservation. 



There are reasons for believing that the San Juan Glacial epoch may have 

 been characterized by small ice-caps among the western ranges rather than by 

 Alpine glaciers, which were the prevailing type during the Big Horn and Uinta 

 epochs. 



There are good reasons for believing that the San Juan eix)ch preceded the 

 development of the great canyons among the mountains, and therefore that 

 much of the sculpturing which bas given form to the scenic features of the 

 range is inter- and post-Glacial in origin. The time relation of the ei>ochs of 

 glaciation to other events in the physiographic history of the range was dis- 

 cussed. 



GLACIAL INVESTIGATIONS IN MINNESOTA IN 1911 

 BY FRANK LEVERETT 



(Ahstract) 



A sheet of old calcareous drift deposited by an ice-sheet radiating from 

 central Canada covers nearly all of Minnesota and extends into western Wis- 

 consin. The prominent moraines of western Minnesota, nainod by Upham 

 Itasca, Leaf Hills, and Fergus Falls, were formed in the order named, as is 

 shown by the glacial drainage from them. The rock constituents of these 

 moraines show remarkable disintegration that suggests a possible pre-Wiscon- 

 sin age. After these moraines were formed by the ice radiating from central 

 Canada, there followe<l an ice-movement radiating from the high tableland 

 northeast of Rainy Lake. This moved across the northern ends of the above- 

 named moraines and extended a few miles beyond the portion of the Mississippi 

 above Saint Paul. This produced the so-called "red drift." After this ice-move- 

 ment waned, there followed a re-advance of the ice-sheet radiating from central 

 Canada which had its main axial movement through the Red-Minnesota -Des 



