1874.] ■ 291 [Shaler. 



6. Transfer of weight from, the sea to the land, by the accumulation 

 of an ice sheet on the land. 



In a previous communication, 1 1 have called attention to the fact that 

 if we suppose the present position of the land to be the result of 

 lateral pressure, we must suppose that it is retained in its position by 

 a continuance of this pressure. If this be the cause, then the accu- v 

 mulation of a mass of ice a mile or so thick may still have a great 

 effect upon the form of the curves of the crust, depressing those 

 regions when the weight is accumulated in the form of ice. We 

 should expect to find that such depression of one part of a continent 

 would be attended by 'an uplift of another region ; this seems to have 

 been the case during the last glacial period, when the continent south 

 of the Hudson seems to have been uplifted, while the northern sec- 

 tion was depressed. At present the southern section is again sinking 

 while the northern shore seems to be generally rising. 



If we proceed to represent to ourselves the amount of elevation of 

 the continent of North America, south of the glacial sheet, necessary 

 to counterbalance the depression below that ice' mass, we are sur- 

 prised at the geographical changes that would necessarily be brought 

 about. It is, in the first place, necessary to notice that we must sup- 

 pose that the elevation would probably not extend to the tropical 

 regions, but would be greatest at a point not far from the borders of 

 the ice sheet, at least, not further from that line than the point of 

 maximum subsidence. Bringing above the water enough of North 

 America to balance the glacial subsidence, we would connect the 

 West Indian Islands with the main land and make the Gulf of Mex- 

 ico and Carribean Sea a Mediterranean. We would, apparently, 

 •have to extend the Atlantic coast to the seaward until it included 

 that part of the bed of the Gulf Stream which passes over a bottom 

 having a mountainous topography. 



In the case of the European continent, a great elevation of its 

 southern part would produce even more important geographical 

 changes than on the American continent. 



There are one or two facts that may be well considered in this con- 

 nection. Along our continents, as has been often noticed, we have a 

 more or less extensive fringe of comparatively shallow water making a 

 sort of shelf beneath the sea, from the outer edge of which the 

 soundings plunge suddenly to the depths of the ocean. May it not 



iSee paper on Recent " Changes of level on the Coast of Maine," Mem. Bost. 

 Soc. Nat. Hist., Vol. II, p. 338. 



