EDITORIALS. 223 



believe to be without foundation. Its fallacy appears when the 

 quantitative elements of the problem are considered. 



Let it be assumed that northward elevation was the cause of 

 the cold climate which made the development of the Pleistocene 

 ice-sheet possible. Let it be assumed further (and this is the 

 assumption most favorable to the doctrine here opposed), that 

 the elevated region was in isostatic equilibrium at the time the 

 ice began to accumulate. Let it be assumed also, that the 

 average specific gravity of the mass of snow and ice of the 

 ice-sheet was one-third that of the rocks of the earth's crust. 

 On the doctrine of isostasy, depression should have accompa- 

 nied the accumulation of snow and ice. When the central part 

 of the snow-field had a depth of 300 feet, the maximum depres- 

 sion which it could have caused, under the assumed conditions, 

 was 100 feet. At the minimum, therefore, the surface of the 

 central part of the ice-field must have been 200 feet higher than 

 the surface of the land before the ice-field formed. Nearer the 

 margins of the ice-field, where the ice was thinner, both the 

 depression of the land surface and the accompanying elevation 

 of the snow surface would have been less ; but each point of the 

 surface of the snow-field must have been higher than the corre- 

 sponding point of the surface of the land at the time the ice 

 began to accumulate, and the temperature at all points must 

 have been correspondingly reduced. Instead of being amelio- 

 rated by the depression of the land surface, the very conditions 

 which brought about this depression were causing the climate to 

 become progressively more severe. When the ice had attained 

 a thickness of 3,000 feet, it might have occasioned a maximum 

 depression of the subjacent land surface to the extent of 1,000 

 feet, and therefore a minimum elevation of the ice surface at the 

 same point, to the extent of 2,000 feet. While, as before, both 

 the depression of the subjacent land surface and the correlative 

 elevation of the surface of the ice-sheet would have been less near 

 the margins of the snow-field than at its center, it still remains 

 true that each point of the entire surface of the ice must have been 

 higher than the corresponding point of the surface of the land at 



