LIFE ON THE EARTH. 155 



northern hemisphere might lose its singular advant- 

 ages of climate, so that glaciers might spread over its 

 valleys now fertile of corn. Changes in the earth's 

 physical features will account for a local augmen- 

 tation of cold, and explain to us the glacial epoch, 

 the phenomena of the boulder drift, and the Arctic 

 fauna which accompanies it. Can we by processes of 

 the same order, taken in another direction, account for 

 the opposite effect of greater heat in the same regions 

 in earlier times? 



The hypothesis of Sir C. Lyell already alluded to, 

 which attributes change of climate to an alteration 

 in the distribution of land and water, though appa- 

 rently not of much efficacy in exalting the mean 

 temperature of the whole surface of the globe, opens 

 beyond doubt a source of real power to change the 

 local climate of any part, and especially to augment 

 the warmth of a tract lying far from the equator. 

 We see this to be strikingly the fact in the case of 

 the gulf-stream running up the Atlantic; and in a 

 less degree in the bending of the isothermals north- 

 ward to Behring's Strait. The maximum effect of 

 such currents, according to the present arrangement 

 of land and water, is seen in the beneficial action of 

 the gulf-stream on the western coasts of the British 

 Islands and Norway: and unless we can imagine a 

 position of the continents more favourable for the 



