1876.] 61 [Wright. 



but after a few miles of grating and rolling along the sides of the 

 glacier, the blocks are reduced to rude rounded forms, never showing 

 any parallel striations; toward the ends of the longer lateral moraines, 

 and especially the terminal moraines, most distant from the source of 

 supply, the blocks are all rounded boulders, not differing greatly from 

 those of a rapid mountain stream. Among these a great deal of 

 gravel and sand has accumulated, and within the region dammed by 

 terminal moraines subsequent glacial silts have become stratified in 

 small pools and lakes. 



"The process by which the lateral and terminal morainal blocks 

 have been thus rounded may be readily studied upon the active gla- 

 ciers of Mount Shasta. These no longer fill their former valleys, but 

 are shrunken streams of ice which flow down the abrupt slope of the 

 volcano's cone, enter the gorges worn by their ancestral glaciers, and 

 are often walled in by abrupt precipices of volcanic rock from 800 to 

 1500 feet in height. The extremes of temperature are constantly 

 cracking and dislodging blocks from the brink and flanks of these 

 mountain walls, and as a consequence the glaciers are far more 

 cumbered by debris than any that can be observed on the Alps. 



" The case of the Mc Cloud glacier, which I have mentioned in a 

 chapter on Shasta flanks in Mountaineering in the Sierra Nevada, is 

 especially interesting from the enormous cumbering piles of debris 

 which overwhelm the lower stretches of the glacier and for at least a 

 mile hide the ice from view. 



" I had for some time supposed that the immense piles of rock 

 which I had seen below the visible limits of the ice were of the na- 

 ture of an ordinary terminal moraine and rested directly upon the 

 bottom of the canon, until I was attracted by a sudden grating and 

 rushing sound in the middle of the region of debris and witnessed a 

 very interesting phenomenon. The ice which underlaid the moraine 

 blocks had evidently melted from the percolation of warm streams 

 and the access of air through either moulins or crevasses. The rotten 

 ice gave way under the load of debris and thousands of tons of rocks 

 sunk down, leaving a conical pit a hundred yards in diameter and 

 not less than a hundred feet deep. Along the brink in one or two 

 places the ice showed through, but was rapidly covered by the 

 avalanches of debris. A second subsidence of this character occurred 

 while I was watching the glacier, and I at length discovered that 

 from a mile to a mile and a half of the end of the ice stream was 

 deeply buried beneath debris. These rocks had not been transported 



