LENTICULAR SHAPE OF COASTAL GEAVEL MASSES. 385 



distort the stratification. So also where flowing ice abutted against a sub- 

 glacial mass of gravel it might often do so unevenly, so that cavities of 

 unequal thickness would lie between the ice and gravel. Into these, if new 

 gravels Avere deposited, the subsequent advance or melting of the ice would 

 change or obliterate the stratification. If such distortions were prevailingly 

 on the stoss side of the gravel hillocks, as they were in the places examined, 

 motion of the ice during the formation of the gravel deposit would be 

 indicated, and also subglacial origin. That subglacial streams abounded 

 near the coast is directly proved by the glacial potholes, also by the pres- 

 ence of the hummocks of glacial gravel directly beneath the Waldoboro 

 moraine, and by other facts. 



The general inference follows that the lenticular kames were formed 

 beneath the ice at a time when it was so thin that it was forced to flow 

 over them without pushing them forward and incorporating them with the 

 till of the terminal moraine, as appears to have been the case at the great 

 outermost terminal moraines. And if these lenticular masses were formed 

 beneath flowing ice, their shapes must be due in part to the same forces 

 that produced the lenticular hills of till. Like the latter, the surfaces of 

 the gravels were molded into the forms of stability by the ice as it flowed 

 over them. But in the case of the drumlin the ice pressure was a com- 

 paratively constant quantity, while in the esker the action of the water in 

 melting and eroding the ice was a controlling agency to change the pres- 

 sure and in part to mold the form. The ice, as it advanced, found the 

 head of its columns literally melting away, so that if the supply of water 

 continued, the enlargement of the channel might often proceed even more 

 rajDidly than the advance of the ice. During the summer time if these 

 lenticular gravel hills were formed at the base of "glacier mills," it is 

 doubtful if the ice could advance so fast as to impinge against the kame. 

 But during the winter, when the supply of water was small and almost 

 all of it ice cold, the amount of melting and erosion would be greatly 

 reduced. Now and then the ice would abut against the gravel and be 

 forced to flow over it, at the .same time helping to carve it into the len- 

 ticular form. Indirectly the flow of the water in the space between the 

 gravel and the ice of the glacier — a space caused by the gradual melting 

 and erosion of the advancing ice — would tend to the broadly arched form 

 of gravels. Yet since the water would erode and melt the ice somewhat 



MON XXXIV 25 



