1868.1 



135 [Shaler. 



we would have one portion of the crust affected by a movement, while 

 the remainder was at rest. In this case there can be no doubt but 

 there would exist a great tendency of the area thus affected to bend 

 downward.^ If the condition of the deeper portions of the earth 

 was such as to admit of the outer crust obeying this tendency to bend 

 downward, as given by the expansion of the beds below, arising from 

 the accumulation of glacial material, there would seem to be no diffi- 

 culty in the way of our finding an explanation of most of the phe- 

 nomena of subsidence connected with glacial action. It is not to be 

 denied that all the evidence goes to show that we can no longer 

 retain that theory of the earth's structure which supposes a hardened 

 outer crust resting upon a fluid or viscid nucleus. But there are 

 many reasons for believing that though the deeper regions of the 

 earth are as rigid as the superficial portions, there exists, nevertheless, 

 a zone not far from the surface where a considerable portion of matter 

 still remains in a sufficiently softened state to admit of considerable 

 movement in the hardened crust which rests upon it. But without 

 attempting to discuss here the question of the nature of the means 

 by which movements of the crust take place, we may safely assume 

 that the conditions do now, and always have admitted a considerable 

 up and down motion of the crust of the earth. How far the glacial 

 sheet may have served to bring about these changes of level, or in 

 what way the ice has operated, are questions which cannot well be 

 discussed until our knowledge of the facts connected with glaciatlon 

 and submergence is more complete. It does not seem to be too haz- 

 ardous, however, to venture the assertion, that the extent of glacial 

 submersion will be generally found to be proportionate to the depth 

 to which the glacial accumulation attained. Not that any fixed 

 ratio will be discovei'able, but that where the glacial sheet was 

 great, the subsequent subsidence was also considerable, and that 

 where the glacial mass attained to no great depth, the subsidence was 

 also slight. If this correspondence should be sufficiently verified, we 

 shall be driven to sujjpose that the phenomena of glaciation and subsi- 

 dence stand to each other in the relation of cause and effect, and that 

 the ice sheet operates not in a general way by the change in the 

 centre of attraction, rising from the circumpolar accumulation, but 



1 Under these circumstances, the behavior of the coast would be exactly illus- 

 trated by the action of a bar composed of two metals having differo' '. coefficients 

 of expansion soldered together (as in the thermometer of Brogue,;. On the appli- 

 cation of heat the bar will be bent, the arc pointing in the direction of that portion 

 of the bar having the greatest coefficient of expansion. 



