182 THE CANADIAN NATURALIST. [Vol. X. 



8. At the present time, the distribution of the trade-winds and 

 monsoons is such as to divo^t a large quantity of warm equatorial 

 water into the northern hemisphere, producing an excess of 

 warmth above that of the S. Hemisphere between latitudes 40'^ 

 and 59° N. 



9. This effect is intensified by the narrowing of the seas to 

 the north, and is of course especially felt on the western sides of 

 the continents. 



10. Not only does the Southern Hemisphere thus lose a large 

 ehare of its warm water, but the effect of the remainder is dissi- 

 pated by bring spread over a vast expanse of sea. 



11. This great expanse of ocean in the Southern Hemisphere 

 is favourable to the deposit of snow and formation of glaciers, by 

 furnishing a great evaporating surface, and at the same time a 

 low general temperature facilitating precipit.itiou. This applies to 

 the Antaictic continent, and also permits the formation of glaciers 

 far to the north in New Zealand and in South America. 



12. On the other hund the present condition of tlie Northern 

 Hemisphere is unfavourable to glaciers, because the sea is so 

 warm that deposition near the coasts is rather as rain than snow 

 up to pretty high latitudes, while the continents are so wide 

 that there is little precipitation in their interior. 



13. Thus there are no glaciers in Eastern Siberia, even in the 

 mountains, where the mean temperature is only 1^^ to 1(3° C, 

 and Central Asia generally is unfavourable to glaciation on 

 account of its dryness, while Eastern Asia is acted on by the 

 monsoons. If, therefore, the extent of land in Asia has not 

 materially changed since the Pliocene period, there could not 

 have been ureat o-laciers there since that period. Even the sub- 

 mergence of the great plain of China could not materially affect 

 this result, thouuh it mii^ht cause glaciers in the mountains of 

 Japan. 



14. To explain the great Post-plioeene glaciers, of which traces 

 are found in Western Europe, it is necessiry to suppose that the 

 temperature was lower, either on account of submergence of the 

 low lands or of diversion of warm currents, or both causes may 

 have operated, A submergence connecting the White and B iltic 

 Seas would greatly promote the production of snow and ice. 

 But tliis could not aff. ct the interior of Russia or of Asia, so 

 long as their plains remained above water. 



15. The submergence of the plains must be a necessary con- 

 dition of the general glaciation of the higlier lands. 



