726 ROLLIN D. SALISBURY 



third factor, of local importance, was the accumulation of snow 

 in catchment basins among the loft}' peaks of two east-west 

 divides, lying west of the main crest. These basins, in many 

 instances, furnished tributary glaciers to the main canyons, and 

 thus greatly increased the amount and strength of the work done 

 by the ice on the west side of the range. 



Glaciation was not only more extensive, but also more vigor- 

 ous on the west side of the range than on the east. This is shown 

 by a more complete cleaning out of loose material from the 

 glaciated valleys of the west slope, by the more complete reduc- 

 tion of their asperities of surface, by the greater deepening of 

 the main canyons on this side, leaving their tributary valleys 

 "hanging" 200 to 300 feet above, and by the development of 

 more massive moraines. The moraines of the east-slope glaciers 

 are insignificant in comparison with those of the west slope 

 glaciers. 



The work of the season removes all doubt as to the duality 

 of the ice age in the Wasatch Mountains. There were at least 

 two ice epochs separated by a long interglacial interval. Evi- 

 dence of more than two epochs was not found. The basis for 

 the above conclusion is as follows : 



1. In several valleys there are outer moraines, much older 

 than the inner moraines of the same valleys. A considerable 

 tunnel exposure in one of these outer moraines showed essen- 

 tially all of the abundant granite bowlders, up to four feet in 

 diameter, so thoroughly disintegrated that they had been cut 

 through with picks and shovels in the excavation of the tunnel. 

 Most of them could be crumbled by the hand. This condition 

 of things was not superficial, but held to the depth of twenty 

 feet, the deepest point of exposure. 



2. In certain glaciated canyons there are such variations in 

 the amounts of postglacial change (weathering, erosion, etc.) 

 which different portions of the drift and valley walls have suf- 

 fered, that it seemed necessary to postulate much longer expo- 

 sure for certain parts than for others. In all such cases, the 

 drift which appears to be older, extends beyond that which 



