392 CAUSES OF CLIMATAL CHANGE 



temperate flora to subsist in Greenland, and to bring all the 

 present temperate regions of Europe and America into a con- 

 dition of subtropical verdure. 



It is only necessary to add that we actually know that 

 changes not dissimilar from those above sketched have really 

 occurred in comparatively recent geological times, to enable us 

 to perceive that we can dispense with all other causes of change 

 of climate, though admitting that some of them may have occu- 

 pied a secondary place. This will give us, in dealing with the 

 distribution of life, the great advantage of not being tied up to 

 definite astronomical cycles of glaciation, which do not well 

 agree with the geological facts, and of correlating elevation and 

 subsidence of the land with changes of climate affecting living 

 beings. It will, however, be necessary, as Wallace well insists, 

 that we shall hold to a certain fixity of the continents in their 

 position, notwithstanding the submergences and emergences 

 which they have experienced. 



Sir Charles Lyell, more than forty years ago, published in 

 his " Principles of Geology ' : two imaginary maps, which illustrate 

 the extreme effects of various distribution of land and water. 

 In one, all the continental masses are grouped around the 

 equator. In the other they are all placed around the poles, 

 leaving an open equatorial ocean. In the one case the whole 

 of the land and its inhabitants would enjoy a perpetual summer, 

 and scarcely any ice could exist in the sea. In the other, the 

 whole of the land would be subjected to an Arctic climate, and 

 it would give off immense quantities of ice to cool the ocean. 

 Sir Charles remarks on the present apparently capricious distri- 

 bution of land and water, the greater part being in the northern 

 hemisphere, and, in this, placed in a .very unequal manner. 

 But Lyell did not suppose that any such distribution as that 

 represented in his maps had actually occurred, though this 

 supposition has been sometimes attributed to him. He merely 

 put what he regarded as an extreme case to illustrate what 



