1875.] 335 [Shaler. 



It will be seen by the inspection of a map that gives the height of 

 the land, that with a depression of two thousand feet below the pres- 

 ent level, we should have had, at the close of the last glacial period, 

 nearly twice the room for the passage of warm currents and cold cur- 

 rents from the pole. This would have led to the immediate return of 

 very warm conditions to that area on the disappearance of the ice 

 mantle of the glacial period. As the land began to rise and the ma- 

 rine currents to be more and more barred out from the poles, the tem- 

 perature would necessarily sink below its former height. 



These considerations, which can be established on purely theoretical 

 grounds, serve very well to explain the observed change which 

 has taken place in Greenland and Iceland within the historical 

 period. It is quite certain that the climate has greatly changed in 

 Greenland since the settlement of that country in the tenth century, 

 and there seems much evidence of a similar change in Iceland. If 

 we suppose that there has been an elevation of only ten feet in a cen- 

 tury of the land about Behring's Strait, the effect upon the move- 

 ment of warm water into the Arctic Ocean might become considera- 

 ble within eight centuries. At present a slender thread of the Japan 

 current reaches through the Strait and seems to affect the condi- 

 tions for some distance to the northward of the north end thereof; 

 eighty feet more added to the depth of water, including what would 

 be gained in width, could not add more than something like a fifth to 

 the heat-carrying power of the northward passing current. Therefore 

 we must look to some greater phase of this cause for the change of 

 the Greenland climate. I think we can find it in the following man- 

 ner ; let us suppose that during the ten thousand years anterior to 

 the present time there has been a constantly diminishing rate of the 

 elevation during equal periods of time, then we may easily suppose 

 that a thousand feet of altitude had been gained during that time, 

 notwithstanding the present slow rate of elevation. Nothing like the 

 present slow rate of upheaval can be supposed adequate to bring 

 about the great re-elevation of the post-glacial time. It must have 

 been far more rapid for a part of the time during which it has been 

 going on. Thus rapidly lifted during the first part of the period of 

 elevation, the accumulation of ice and the intensification of the cold 

 would hardly keep pace with the change of elevation, but would con- 

 tinue for a while after the beginning of the elevation at a rate hardly 

 to be explained by the elevation itself. In other words, the increasing 

 cold observed in Greeland since the occupation of that country by 



