Staler.] . 334 [January 20, 



other is barred from the circumpolar region by the closure of the 

 land and islands about Behrings Strait. If this barrier to the north- 

 ern movement of the Japan current could be removed we should 

 have a very great increase in the circumpolar temperature; how 

 great this increase would be may be judged from an inquiry into the 

 present effects of the heat carried from the equator to the inter-arc- 

 tic regions. 



The computations of Mr. James Croll make it quite evident that 

 the amount of this heat carried from the equator to the poles in the 

 present state of the oceanic currents, is so great that the temperature 

 of that part of the earth within the Arctic Circle is brought up to 

 nearly twice the height above the zero of Fahr. that it would have 

 under conditions when no heat was received by this channel. His 

 calculations show that all the heat falling within two hundred and 

 ten miles of either side of the equator passes to the !North Atlantic, 

 and goes to determine the average heat of that region. If this be 

 the case, it is clearly seen that the admission of another current of 

 the same dimensions must elevate the mean annual temperature of 

 this region to somewhere between 55°-60° Fahr. This is not far from 

 the mean annual temperature of the Ohio valley ; so we have the nec- 

 essary elevation of temperature. So far these considerations are, in a 

 general way, self-evident, and must have suggested themselves to most 

 persons who have considered this problem ; the point which has suffi- 

 cient importance to warrant farther discussion is the connection be- 

 tween the elevation and subsidence of this land barrier, which shuts 

 the larger part of the equatorial waters away from the circumpolar re- 

 gion, and great changes in the temperature of the northern waters. 

 It is now a well ascertained fact that during the last glacial period 

 the land about the poles was very much depressed below its present 

 level. Occurring in both hemispheres and over all the circumpolar 

 land, this subsidence is certainly connected in some way with the for- 

 mation of a great, sheet of ice. I have endeavored to show the nature 

 of this connection, and to prove that it arises from the direct weight 

 of the ice ; but as this does not necessarily concern us in our present 

 inquiry, I shall content myself with the assumption which I believe 

 amply justified by the fact, that the formation over the land of an ice 

 sheet leads necessarily to great subsidence. At the close of each 

 glacial period, when the ice sheet passes away, the circumpolar re- 

 gions must be far more open to the passage of warm water toward 

 high latitudes than at any other time. 



