CHAP, xviii. TO AFFECT CLIMATE. 365 



graphical change in post-pliocene times. But a difficulty of 

 another kind presents itself. We have seen that, during the 

 glacial period, the cold in Europe extended much farther south 

 than it does at present, and in this chapter we have demon 

 strated that in North America the cold also extended no less 

 than 10 of latitude still farther southwards than in Europe; so 

 that if a great body of heated water, instead of flowing north 

 eastward, were made to pass through what is now the centre 

 of the American continent towards the Arctic circle, it could 

 not fail to mitigate the severity of the winter's cold in pre 

 cisely those latitudes where the cold was greatest, and where 

 it has left monuments of ice-action surpassing in extent any 

 exhibited on the European side of the ocean. 



In the actual state of the globe, the isothermal lines, or 

 rather the lines of equal winter temperature, when traced 

 eastward from Europe to North America, bend 10 south, 

 there being a marked excess of winter cold in corresponding 

 latitudes west of the Atlantic. During the glacial period, 

 viewing it as a whole, we behold signs of a precisely similar 

 deflection of these same isochimenal lines when followed from 

 east to west ; so that if, in the hope of accounting for the 

 former severity of glacial action in Europe, we suppose the 

 absence of the Grulf Stream and imagine a current of equi 

 valent magnitude to have flowed due north from the Grulf of 

 Mexico, we introduce, as we have just hinted, a source of heat 

 into precisely that part of the continent where the extreme 

 conditions of refrigeration are most manifest. Viewed in this 

 light, the hypothesis in question would render the glacial 

 phenomena described in the present chapter more perplexing 

 and anomalous than ever. But here another question arises, 

 whether the eras at which the maximum of cold was attained 

 on the opposite sides of the Atlantic were really contem 

 poraneous? We have now discovered not only that the 

 glacial period was of vast duration, but that it passed through 



