Shaler.] 128 [June 16, 



movement possible to water under- these conditions would be very 

 small; but in the continual recurrence and cessation of strains these 

 slight movements would integrate themselves into a steady transfer of 

 water towards the border of the glacier. The occurrence of these 

 meltings, and the accompanying change of volume in different parts 

 of the ice sheet, would necessarily have the effect of continually alter- 

 ing the tensions in all parts of the mass; this change would be ex- 

 ceedingly favorable to the creation of a constant succession of ten- 

 sions, and the consequent frequent melting and freezing of the water. 

 One of the first consequences will be to reduce the aggregate friction 

 of the base of the ice upon the earth., on account of the ice being 

 essentially afloat whenever this melting occurs beneath it, the solder- 

 ing of every crevice in the superincumbent ice being assured by the 

 freezing of the water as soon as released from the superincumbent 

 pressure. Another important effect would arise from the penetration 

 of the earth to great depths by the glacial water injected by a pres- 

 sure equal to the weight of the whole thickness of the ice sheet. If 

 a reservoir of water was formed beneath the ice in any depression 

 the result would be, in case of the long retention of the water that 

 its temperature would become considerably elevated above the point 

 at which it was made molten by pressure. If, now, the barrier sep- 

 arating this mass of water from a region of less pressure even be 

 taken away, there would be a rush of water in that direction which 

 might assume great importance as an erosive and transporting agent. 

 I have long remarked in the study of our American moraines 

 that by far the larger part of the pebbles were water worn, and that 

 scratched specimens even in regions high above the sea, where ma- 

 rine action was quite out of the question, and did not form more 

 than one per cent., often not one tenth of one per cent, of the whole 

 mass. It is well nigh impossible to account for this great abundance 

 of rounded pebbles without supposing there were powerful currents of 

 water beneath the glacial mass. It seems to me that the melting of 

 the water by pressure, and the elevation of the temperature of this 

 water by the heat generated by friction, or taken from the earth, 

 would probably give us sufficient movement of water to produce con- 

 tinued or interrupted currents beneath a large part of the ice sheet. 

 This will also help us to account for the formation of glacial basins, 

 and for the deep valleys of the Fjord Zone, inasmuch as melting oc- 

 curs on account of the pressure ; the points where the ice is deepest 

 will be the places where melting occurs most easily. Let us consider 



