PLEISTOCENE GEOLOGY OF THE SAWATCH RANGE 701 



of terminal moraines in the former case has been noted. In glaciers 

 of the Lake Fork type, the ice deployed on the plain at the base of 

 the mountains, and enormous quantities of drift were piled up in the 

 form of terminal moraines. The terminal moraines often have 

 abrupt outer faces, 200 to 300 feet high, and are marked by a char- 

 acteristically irregular, hummocky topography. 



The terminal moraines are continuous with and merge into the 

 lateral moraines in the mountain valleys. The lateral moraines are 

 often large and he against the valley walls, their crests sloping down 

 the valley. The crests of the lateral moraines are over 700 feet 

 above the stream in some parts of the valley of Clear Creek, and 

 descend with an even slope of 200 to 400 feet a mile down the valley. 

 Beyond the mountains, the lateral moraines tend to flatten out, and 

 merge into extensive terminal moraines. 



Little detailed work was done on the glaciation of the Park Range, 

 but it is known that ice of the last glacial epoch occurred in the 

 "gulches" east and southeast of Leadville; in the valleys of the East 

 Fork of the Arkansas River, Ten-mile Creek, and over a considerable 

 portion of the east slope of the Park Range. 



The older drift. — In a number of places within the area studied 

 there are tracts covered with scattered bowlders or bodies of drift, 

 which are certainly of glacial origin, but which are much older than 

 the drift of the last ice epoch. In these patches the present topog- 

 raphy is due to erosion, all signs of kettles, or irregular hummocks, 

 having disappeared. The rock outcrops have generally been weath- 

 ered into sharp crags, a change which certainly required much more 

 time than has elapsed since the last glacial epoch. The surface 

 bowlders, too, are often weathered considerably, crumbling to pieces 

 under the hammer. 



The evidence that this drift is glacial is found along several lines. 

 The bowlders are of a size which would militate against a fluvial 

 origin. Strife are sometimes found on the under, unweathered sur- 

 faces of the bowlders, or on the faces of those in fresh cuts in the 

 drift. The distribution is such as would be expected from older 

 and more extensive glaciers, for the drift in question occurs just 

 outside the new drift, or above it on benches to which the last ice 

 did not reach. The patchiness of the old drift is due largely to 



