Shaler.] 134 [October 7, 



to which, the sea attained in different regions, it might, with allowance 

 for recent alterations of level, show an equality of submergence of all 

 shores under the same parallel. But until such conjectures are proven, 

 we cannot accept the comparative elevation of ancient shore lines in 

 different latitudes, as evidence of Mr. Crool's hypothesis. A further 

 objection is to be found in the irregularities in the movements in high 

 Northern regions. If the formation of a large ice cap about the pole 

 was the cause of the subsidence of Northern regions, then we would 

 expect something like uniformity in the action of the sinking ; but in 

 Scandinavia and elsewhere, we have evidence of repeated alternations 

 of elevation and subsidence, which could be explained in no other 

 manner than by the unsatisfactory conjecture, that for some unknown 

 reason the ice cap was subject to sudden alternations of level. The 

 changes of level now going on on Northern shores, seem to be but a 

 continuation of the modifications which have left their traces in the 

 ancient littoral phenomena of those regions, and yet all these move- 

 ments are not elevatory ; part of the shore of Scandinavia is indeed 

 rising, but another portion is subsiding, and a large part of the west 

 shore of Greenland is undoubtedly undergoing a gradual depression. 



If any value whatever is to be given to the theory of Mr. Crool, 

 there Avould still remain very important cooperative actions, which 

 would have to be understood before the whole of the phenomena 

 could be explained. On consideration, it will appear probable that 

 important effects on the position of the land surfaces would be exer- 

 cised by the rise in the isogeothermals from the non-conducting 

 power of the ice cap of the glacial period. 



The accumulation of seven thousand feet of ice upon any one por- 

 tion of the earth's crust must, it would seem from its great non- 

 conductive power, exercise as great an effect upon the temperature 

 of the rocks below, as would the addition of an equal thickness of 

 ordinary sedimentary nature; that is to say, the lines of equal heat 

 would move outwards from the centre to the extent of three thousand 

 feet. This increased temperature of the deeper portions of the 

 earth's outer crust, would necessarily be attended by an expansion of 

 the materials composing such crust. If the substance thus affected 

 by heat, had the coefficient of expansion belonging to gi-anite, and the 

 diameter of the region affected be supposed to be one thousand miles, 

 then the amovmt of this expansion would be about thirty-seven hun- 

 dred feet. Now inasmuch as the uppermost part of the crust, i. e. the 

 ice sheet, would not partake of this increase of temperature, and would 

 not have its bulk affected by the movement of the isogeothermals. 



