Studies in the Sierra 



191 



tions made by small streams. A few slate boulders from the 

 Lyell group may be seen, but the main mass of the moraine is 

 composed of ordinary granite and porphyry, the latter having 

 been derived from Feldspar and Cathedral valleys. 



The elevation of the top of the moraine near Cathedral trib- 

 utary is about 8100 feet ; near Half Dome, 7600. It rests upon 

 the side of the valley at angles varying from fifteen to twenty- 

 five degrees, and in many places is straight and uniform as a 

 railroad embankment. The greatest depth of the glacier be- 

 tween Clouds Rest and Mount Starr King, measuring from the 

 highest points of its lateral moraines, was 1300 feet. The re- 

 currence of ridges and terraces on its sides indicate oscillations 

 in the level of the glacier, probably caused by clusters of cooler 

 or snowier seasons which no doubt diversified the great glacial 

 winter, just as clusters of sunny or stormy days occasion fluc- 

 tuations in the level of the streams and prevent monotony in 

 our annual winters. When the depth of the South Lyell Glacier 

 diminished to about 500 feet, it became torpid, on account of 

 the retardation caused by the roughness and crookedness of its 

 channel. But though it henceforth made no farther advance of 

 its whole length, it possessed feeble vitality — in small sections, 

 of exceptional slope or depth, maintaining a squirming and 

 swedging motion, while it lay dying like a wounded serpent. 

 The numerous fountain wombs continued fruitful long after 

 the lower valleys were developed and vitalized with sun-heat. 

 These gave rise to an imposing series of short residual glaciers, 

 extending around three sides of the quadrangle basin, a dis- 

 tance of twenty-four miles. Most of them have but recently 

 succumbed to the demands of the changing seasons, dying in 

 turn, as determined by elevation, size, and exposure. A few 

 still linger in the loftiest and most comprehensive shadows, ac- 

 tively engaged upon the last hieroglyphics which will complete 

 the history of the South Lyell Glacier, forming one of the no- 

 blest and most symmetrical sheets of ice manuscripts in the 

 whole Sierra. 



ILLILOUETTE 



The broad, shallow glacier that inhabited the basin of Illilou- 

 ette more resembled a lake than a river, being nearly half as 

 wide as it was long. Its greatest length was about ten miles. 



