9S BELT ON THE GLACIAL PERIOD IN NORTH AMERICA. 



inland more than once the poles on which their large boats are 

 placed. Here again the rate of motion is greatest towards the pole. 

 The present period of subsidence was preceded in part of east- 

 ern North America by one of elevation, which brought up the marine 

 deposits of the Champlain period ; to '\\ hich the Montreal beds 

 already mentioned belong. On the southeni borders of New Eng- 

 land these marine beds are only found up to about forty feet above 

 the sea. As we proceed north they are found higher and higher. 

 At Montreal they i-each to five hundred feet above the sea, and in 

 the extreme north, on Cornwallis and Beechey Islands in Barrow 

 Straits, they have been found at an elevation of over one thousand 

 feet. Here again the elevation is greatest towards the pole and 

 gradually decreases southwards. To produce extrem.e cold accord- 

 ing to Sir (Jhas. Lycll's theory, we only require a similar movement 

 on a larger scale, and these smaller oscillations with their A^ertices 

 towards the pole, may point to some general law governing the up- 

 heaval and subsidence of the earth's crust which would, if it could 

 be deduced, explain the elevation of the land towards the north and 

 its depression towards the south during the glacial period. 



3. Effect of sJmUhig off ivarm currents from the Polar Basin. — We 

 do not know how small a change in the distribution of land and 

 water might again produce a glacial climate. The effect of a change 

 in the direction of the Gulf Stream, has been discussed by Mr. Hop- 

 kins and other writers, but I do not think that it has been noticed 

 that a much greater change of climate would be produced, if all 

 warm currents were shut off from the polar basin. Sir John Her- 

 schel has indeed stated that if Behring's Straits, AAliich are only thirty 

 miles broad, were closed so as to prevent the water circulating from 

 a warmer region, fzndiag its way into the polar basin, there would 

 probably be a continual accretion of ice which might rise to a moun- 

 tainous height.* 



But if, besides the closing of Behring's Straits, there were ti 

 partial emergence of land from beneath the ocean, connecting Europe 

 through Iceland and Newfoundland with America, we can scarcely 

 appreciate the effect it would have in altering the climate of the 

 northern hemisphere. There would not only be a great lowering 

 of temperature through the increase of land around the poles, but 

 ♦Herschel's l*liysic;il Geograpliy, page 41. 



