ANOTHER POSSIBLE CAUSE OP THE GLACIAL EPOCH. 147 



1,000 miles under the rays of a tropical sun. If we allow 

 two degrees for this, then the total loss of heat on passing 

 the coast of Florida will have been ten degrees as compared 

 with that of the present day; and instead of crossing the 

 40th parallel with a surface temperature of 84° Fahr. as 

 stated above, the Gulf Stream of the period referred to 

 would have only had a temperature of 74° Fahr., which 

 would not be very much in excess of the summer 

 temperature of the waters due to latitude at this parallel.* 



We have now to inquire what would be the effect of so 

 great a reduction of temperature upon the climate of the 

 North Atlantic and adjoining regions. A diminution of ten 

 degrees of heat as compared with that of the present day 

 would undoubtedly exercise a very important influence on 

 the climate of the regions bordering the North Atlantic and 

 the coast and islands of the Arctic Ocean. Not only would 

 the annual mean temperature be considerably reduced, but 

 the increase of snow and ice over those tracts which are at 

 present on the verge of perpetually glacial conditions would 

 have the effect of lowering the temperature far beyond their 

 own limits. As Lyell has truly observed, land in Arctic 

 regions conduces to cold ; and owing to the great extent ot 

 additional land in Europe and Asia which would be brought 

 under the influence of an Arctic climate by the lowering of 

 the temperature, the cold would be increased in the 

 adjoining regions lying to the south. 



There is one way, perhaps the only way, by which Ave 

 may indicate diagraramatically the climatic conditions of 

 which we are in search under the hypothesis of a North 

 Atlantic current taking the place of the Gulf Stream, but 

 with a temperature ten degrees lower than the latter. If 

 we suppose that the annual mean temperature of all those 

 regions influenced by the Gulf Stream as far south as (say) the 

 parallel of 40° N. is reduced by about ten degrees below its 

 present range, then we shall have the present isotherm of 



* Eennell has calculated that the waters of the Gulf Stream on leaving 

 the Gulf of Mexico with a surface temperature of 86° Fahr. are 10° above 

 that of the Atlantic in the same latitude ; quot. by Lyell, Principles ; 

 2nd edition, p. 244. A portion of the waters of the equatorial branch 

 even now passes along the east coast of the West India Islands, ultimately 

 joining the Gulf Stream. All this time however they are acquiring heat, 

 but not to the extent which would be the case if they followed the main 

 stream. The amount, however, is unimportant in its bearing on the 

 question before us, as the conditions of this branch of the Equatorial 

 current would have suffered no change. 



