2 32 THE JOURNAL OF GEOLOGY. 



former lake. These pyramids frequently have a height of 60 or 

 80 feet, and are sometimes nearly conical in shape. They resem- 

 ble " sand cones," but are of much greater size and are sheathed 

 with coarser debris. The sand cones are usually, if not always, 

 formed and melted away during a single season, while the debris 

 pyramids require several seasons for their cycle of change. 



Like the lakelets to which they owe their origin, the debris 

 pyramids are confined to the stagnant portions of the glacier and 

 play an important part in the breaking up and comminution of 

 the material forming the marginal moraines. Owing to the slid- 

 ing of the bowlders and stones into the lakelets and their subse- 

 quent fall from the sides of the pyramids, they are broken and 

 crushed so that the outer portion of the glacier, where the pro- 

 cess has been going on longest, is covered with finer debris and 

 contains more clay and sand than the inner portions. 



Just how the holes containing glacial lakelets originate it is 

 difificult to say, but their formation seems to be initiated, as 

 already suggested, by the melting back of the sides of crevasses. 

 Breaks in the general sheet of debris covering the glacier expose 

 the ice beneath to the action of the sun and rain, which causes it 

 to melt and the crevasses to broaden. The openings become 

 partially filled with water and lakelets are formed. The waves 

 wash the debris from the ice about the margin of the lakelets, 

 thus exposing it to the direct attack of the water, which melts it 

 more rapidly than higher portions of the slopes are melted by 

 the sun and rain. It is in this manner that the characteristic hour- 

 glass form of the basins originates. The lakelets are confined to 

 the outer or stagnant portion of the glacier, for the reason that 

 motion in the ice would produce crevasses through which the 

 water would escape. Where glacial lakelets occur in great num- 

 bers it is evident that the ice must be nearly or quite stationary, 

 otherwise the basins could not exist for a series of years. The 

 lakelets and the pyramids resulting from them are the most 

 characteristic features of the outer border of the glacier. The 

 number of each must be many thousand. They occur not only 

 in the outer portion of the barren moraine, but also throughout 



