GEOLOGICAL SEASONS. 181 



tain regions are determined by the existing distribution 

 of oceanic currents is a fact which all admit, and which 

 will be further mentioned in another part of this chapter. 

 But to be an adequate cause of the existence of an arctic 

 climate in regions now temperate there must have been 

 a transposition of land and water much more extensive 

 than is allowed by the admitted persistence of the oceanic 

 basins, and the great continental areas. Moreover, it is 

 very difficult to conceive a distribution of land and water 

 which would bring an arctic temperature to New Eng- 

 land, New York and Ohio. Most of all, such a theory is 

 not adapted to the explanation of a succession of ice-periods. 

 Again, northern elevation has been cited as a cause ade- 

 quate to effect the glaciation of the northern hemisphere. 

 Professor Dana, with his usual insight into the symmetry 

 and coordination of things, has directed our attention to 

 the fact that the growth of the continent of North America 

 was, for many ages, toward the southeast and the south- 

 west. When these borders seemed complete the work of 

 development was transferred to the north, and the north- 

 ern border of the continent was worked out. The develop- 

 ment of the land was always effected through a succession 

 of elevations. When considerable elevation had been pro- 

 duced in the northern regions, the climate of the zone 

 felt the effects ; just as southern Austria and northern 

 Italy receive a chill from the Alpine ranges which lie 

 on the north of them, and render the winters of Verona 

 and the Tyrol much severer than those of Berlin and 

 Hamburg. It cannot be denied that northprn elevation 

 would materially influence the climate of the temperate 

 zone, but it may be doubted whether the influence would 

 amount to universal glaciation, even if we assume north- 



