THE TILL. 271 



until it is clearly proved that there have been no slides at the places of 

 observation. 



A fundamental question regarding the till relates to its origin. The 

 hypothesis of Torell — that part of the morainal matter of the ice-sheet was 

 beneath the ice, while the aipper portion was distributed through the lower 

 part of the ice — has since 1877 appeared to me to explain satifactorily the 

 facts as observed in Maine. The principal considerations bearing on the 

 subject are the following: 



We do not know how the age of ice began. Looking at it from the 

 standpoint of our present climatic conditions, it would most naturall)^ come 

 on gradually. After a time local glaciers filled the mountain valleys. 

 Above them rose cliffs that had been rent into loose blocks during the long 

 ages preceding. Much of this cliff debris fell down upon the ice and 

 formed moraines like those of the Alpine glaciers. But more snow con- 

 tinued to fall than melted, and the time came when this morainal matter 

 and the hills were overtopped by the snow and ice. Unless the higher 

 peaks of the White Mountains and Mount Katahdin be exceptions, all the 

 territory was covered. The proof of this is conclusive, since the rocks on 

 the hills are scored and afford drift bowlders transported from the north. 



So, too, during the decadence of the ice-sheet the tops of the higher 

 hills appeared above the ice long before the flow in the valleys ceased. The 

 glacier had just swept over the cliff's and removed most of the talus and 

 bowlders of decomposition; few therefore would fall upon the ice. The 

 melting of the upper portions of the ice would leave many bowlders on 

 the higher and steeper parts of the hills in such unstable equilibrium that 

 now and then, as one was freed from the embrace of the ice, it would roll 

 or slide down the slopes onto the ice that still remained in the lower parts 

 of the valleys. At this time landslides of the freshly deposited material 

 would naturally be frequent. In these ways it may be admitted as possible 

 that morainal matter was at this period precipitated from above upon the 

 ice, after the manner of ordinary valley glaciers. But if moraines were 

 thus accumulated we ought now to find them, in the form of ridges and 

 trains of bowlders, especially at the flanks of the high, steep hills. On 

 the contrary, the bowlder trains are in lee of granite knobs, where a cliff 

 was shattered beneath the ice and its bowlders pushed forward. While, 

 then, we may grant a limited fall of debris from above onto the top of the 



