Yosemite National Park. 



205 



panying fine debris. Most of them lie in places where it seems 

 likely from the character of the topography and from the 

 courses pursued by the ancient glaciers that heavy continuous 

 moraines once existed. The majority of the boulders are com- 

 posed of extremely durable types of rocks which weather and 

 disintegrate more slowly than most of the rocks in the moraines 

 of the Yosemite region. It is thought that these boulders are 

 the last remnants of moraines of a very early glaciation ante- 



Phofo by F. C. Calkins, U. S. Geol. Survey 



FIG. 62. Glacial boulder at base of Sentinel Dome, on Glacier Point. 

 The boulder is located near the trail leading to Sentinel Dome. This with 

 other boulders marks the highest level reached by the ice of the (earliest) 

 Glacier Point stage, 3,600 feet above the floor of the gorge below. 



dating the El Portal stage. A number of the boulders in ques- 

 tion lie on the broad divide east of Mount Starr King, between 

 200 and 400 feet above the highest moraines of the El Portal 

 stage. The fact that only a few sparse boulders now remain 

 would seem to show that a long period has elapsed since the ice 

 deposited what is thought was probably a continuous and con- 

 siderable moraine. It seems reasonable to infer that these boul- 

 ders belong to a stage of glaciation earlier than the El Portal. 



