200 DRIFT DEPOSITS OF MANCHESTER 



which are the sources of heat, are very une- 

 qually distributed in the heavens, Poisson thought 

 that the solar system, in its journey towards the 

 constellation Hercules, might pass through spaces 

 of very different temperatures ; and that, at some 

 ancient and remote period, it might have passed 

 through a region of the heavens much colder than 

 that in which it is now moving. 



" A much simpler explanation of the change has 

 been proposed by Mr. Lyell. Founding on prin- 

 ciples developed by Humboldt, he observes that 

 the climate of any part of the globe depends, in 

 a great degree, on the distribution of sea and 

 land. The east side of all extensive continents, 

 in the extra tropical regions, has a warmer sum- 

 mer and a colder winter than the western. The 

 extremes of heat and cold, for instance, are incom- 

 parably greater in Lower Canada than in the 

 Oregon territory, though they are both in the 

 same latitude. Now, if North America, at one 

 time extended much farther eastward ; if, for 

 instance, it occupied all the portion of the Atlantic 

 between Newfoundland and Britain ; in that case 

 it is certain that Britain would have had the inhos- 

 pitable climate of Labrador, or even one still 

 more severe, like that of Greenland. There are 



