THE HISTORY OF THE NORTH ATLANTIC 8 1 



Antarctic Sea. No g^logical facts are indeed at first sight 

 more strange and inexplicable than the changes of climate in 

 the Atlantic area, even in comparatively modern periods. We 

 know that in the early Tertiary temperate conditions reigned as 

 far north as the middle of Greenland, and that in the Pleisto- 

 cene the Arctic cold advanced until an almost perennial winter 

 prevailed half way to the equator. It is no wonder that nearly 

 every cause available in the heavens and the earth has been 

 invoked to account for these astounding facts. I shall, I trust, 

 be excused if, neglecting most of these theoretical views, I 

 venture to invite attention, in connection with this question, 

 chiefly to the old Lyellian doctrine of the modification of 

 climate by geographical changes. Let us, at least, consider 

 how much these are able to account for. 



The ocean is a great equalizer of extremes of temperature. 

 It does this by its great capacity for heat, and by its cooling 

 and heating power when passing from the solid into the 

 liquid and gaseous states, and the reverse. It also acts by its 

 mobility, its currents serving to convey heat to great distances, 

 or to cool the air by the movement of cold icy waters. The 

 land, on the other hand, cools or warms rapidly, and can 

 transmit its influence to a distance only by the winds, and the 

 influence so transmitted is rather in the nature of a disturbing 

 than of an equalizing cause. It follows that any change in the 

 distribution of land and water must affect climate, more espe- 

 cially if it changes the character or course of the ocean currents. 



Turning to the Atlantic, in this connection we perceive that 

 its present condition is peculiar and exceptional. On the one 

 hand it is widely open to the Arctic Sea and the influence of 

 its cold currents, and on the other it is supplied with a heating 

 apparatus of enormous power to give a special elevation of 

 temperature, more particularly to its eastern coasts. The great 

 equatorial current running across from Africa is on its 

 northern side embayed in the Gulf of Mexico, as in a great 



