190 Frank Carney 



remains rigid, as its crystalline nature requires. Instead of assigning 

 a slow viscous fluidity, like that of asphalt, to the whole mass, which 

 seems inconsistent with its crystalline character, it assigns a free fluJ"iity 

 to a succession of particles that form only a minute fraction of the whole 

 at any instant. 



This conception is consistent with the retention of the granular con- 

 dition of the ice, with the heterogeneous (in the main) orientation of the 

 crystals, with the rigidity and brittleness of the ice, and with its strictly 

 crystalline character, a character which a viscous liquid does not possess, 

 however much its high viscosity may make it resemble a rigid body.^ 



THE WORK DONE BY GLACIERS 



There are two methods of determining the work done by the 

 continental glacier. We may study ice masses in existence to- 

 day. Glaciers of the Alpine type are found on every continent. 

 Greenland, an island 512,000 square miles in area, is almost 

 entirely covered with ice; this is an ice cap, and approximates a 

 continental glacier. In Antarctica there exist extensive ice areas, 

 while in Alaska there are many splendid examples of the Piedmont 

 or Malaspina type of Glacier. Relative to their size, these glaciers 

 give many suggestions of the work that the continental glacier, 

 such as once covered our part of North America, must have done. 

 Another method of unraveling the activities of the ancient ice 

 sheet is to study the evidences which it left. It made great accumu- 

 lations of drift, it has worn and polished rock surfaces, has carved 

 deeply elsewhere into the rock, has silted up river valleys lead- 

 ing away from the glaciated areas, and has produced complex 

 soils, by bringing together material from distant parts. 



The glaciers now in action are tearing away and building up. 

 So far as we can determine, the glaciers of the past did the same. 

 Glacial work consists of erosion, transportation and deposition. 

 Sometimes these factors appear to be of equal weight. In other 

 areas, one or the other is in the ascendant. Naturally erosion and 

 deposition are opposed, and cannot be in operation in the same 

 place at the same time. 



EROSION BY GLACIERS 



A country once glaciated always bears the scars of icework. 

 No other natural agencies derade and aggrade just as glaciers do. 



1 Chamberlin and Salisbury, Geology, vol. i, (1905), pp. 299-301. 



