14 THE K'K A(iK L\ CANADA. 



tlie snow-line: ami lliut cases in whicli, in sncli latitudes, 

 <;'liic'iers extend nearly to tlie sea-level, oecur only where 

 the mean teni})eratun' is reduced by cold ocean currents 

 a])])r(iacliin,t,' to lii,u;li land, as for instance in Terra del 

 Fue<'() and the southern extremity of South America. 

 ]]ut the temperate regions of Xorth America could not be 

 covered with a permanent mantle of ice under the existing 

 conditiijus of solar radiation : for even if the whole were 

 elevated into a table-land, its breadth would secure a 

 sullicient summer heat to melt away the ice, except from 

 high mountain peaks. 



" 2. It seems physically impossible that a sheet of ice, 

 such as that sujiposed, could move over an uneven 

 surface, striating it in directions uniform over vast areas, 

 and often dii'lerent from the i>resent inclinations of the 

 surface. (Uacier-ice may move on very slight slopes, but 

 it must follow these [since gravitation, along with the 

 more (jr less plastic nature of the ice, has been shown to 

 be the cause of its motion]: and the only result of the 

 innnense accunndation of ice supposed, would be to 

 jjrevent motion altogether by the want of slo})e or the 

 counteraction of opposing slopes, or to induce a slight and 

 irreuular motion toward the margins or outward from the 

 more prominent protuberances. 



" It is to.be observed, also, that, as Ho})kins has shown, 

 it is only tl\e sUditig motion of glaciers that can polish or 

 erode surfaces, and that any internal changes resulting 

 from the mere weight of a thick mass of ice resting on a 

 level surface, could have little or no influence in this way. 



" ?>. The transport of ijoulders to great distances, and 

 the lodgment of them on hill-tops, could not have been 

 occasioned by glaciers. These carry downward the blocks 

 that fall on them from wasting cliff's. But the universal 



