WOODWARD, POLAR GLACIATION, ETC. 603 



Applying this result to the solution of the problem of insular 

 floras and faunas, he points out that their derivation has usually been 

 explained by supposing such islands to have been at one time 

 joined to the continents nearest to them, and to each other in Post- 

 Tertiary times. In every case, therefore, the last movement has 

 been one of depression, the bridge by which they passed over has 

 been submerged and destroyed 



It is a significant fact, first noticed by Wallace that, whilst 

 all islands having shallow channels, however broad, separating 

 them from each other, and from not distant continents, give evi- 

 dence of a former connection in Post-Tertiary times ; on the other 

 hand, islands surrounded by deep water are marked by peculiar 

 faunas. Thus Madagascar, though near the coast of Africa, is 

 separated by a deep sea, and its fauna and flora are singularly 

 distinct. The Galapagos islands have also a peculiar fauna, indi- 

 cating the antiquity of their insulation. 



A uniform lowering of the sea-level would aff'ord a satisfactory 

 solution of these difficulties which cannot so readily be explained 

 by local subsidences and elevations 



A rise of the sea, owing to the increase of its volume — liberated 

 after the Glacial Period from the ice of the Polar regions — would 

 produce the same effect as the lowering of the land, which might 

 not occur generally with the same precision of level as that of the 

 waters of the ocean. 



The continent of South America, and indeed the mountain- 

 chains generally, all over the world, testify to the fact that they 

 have been glaciated to lower levels upon their slopes than that to 

 which ice and snow now descend, or where they occur peiennially. 

 A general lowering of the sea-level would produce precisely the 

 same effect on climate as the raising of the continental surfaces ; 

 the atmosphere, following down, would bring the freezing point so 

 much lower than it otherwise would be. 



An increase in the present obliquity of the Ecliptic would not 

 only permit a greatly increased accumulation of ice on Circum- 

 Polar lands, but it would be the cause of lowering the mean tem- 

 perature of the Tropics ; so that the snow -line would even descend 

 still further from increased precipitation, due to the greater "evapo- 

 ration 



If, as Mr. Belt concludes, the melting as well as the accumu- 

 lation of the ice of the Glacial Period must have occupied thou- 

 sands of years in accomplishment, this is quite in accordance with 

 the gradual growth of coral-reefs, and the silting up of deltas 

 filled with freshwater deposits. But probably some sudden rises 

 did from time to time occur, causing local floods and the inun- 

 dation of vast low-lying tracts of country. 



Since the close of the great Ice-age, there is clear and indis- 

 putable evidence of the Rise of Land * both towards the North 

 and the South Pole, which is probably even now in progress. , . . 



* See above t Mr. Howortii on the Elevatiou of the Circumpolar Regions. 



— Editor. 



