SUMMER DAYS AT MOUNT SHASTA 



to erosion, and the disturbance caused by 

 inter- and post-glacial eruptions, have ob- 

 scured or obliterated those heavier characters 

 of the glacial record found so clearly in- 

 scribed upon the granite pages of the high 

 Sierra between latitude 36 30' and 39. This 

 much, however, is plain: that the summit of 

 the mountain was considerably lowered, and the 

 sides were deeply grooved and fluted while it 

 was a center of dispersal for the glaciers of the 

 circumjacent region. And when at length the 

 glacial period began to draw near its close, 

 the ice mantle was gradually melted off around 

 the base of the mountain, and in receding and 

 breaking up into its present fragmentary con- 

 dition the irregular heaps and rings of moraine 

 matter were stored upon its flanks on which 

 the forests are growing. The glacial erosion of 

 most of the Shasta lavas gives rise to detritus 

 composed of rough subangular boulders of 

 moderate size and porous gravel and sand, 

 which yields freely to the transporting power 

 of running water. Several centuries ago im- 

 mense quantities of this lighter material were 

 washed down from the higher slopes by a flood 

 of extraordinary magnitude, caused probably 

 by the sudden melting of the ice and snow dur- 

 ing an eruption, giving rise to the deposition 

 of conspicuous delta-like beds around the base. 

 35 



