p % oduced by great Geographical Changes. 883 



dity produced by this north and south alignement of continent 

 upon the capacity of what are considered the inhabitants of 

 warm countries to support a very inclement climate. Here is 

 found the fuchsia having perennial foliage, but which when 

 transported to the dry but less inclement climate of England 

 becomes deciduous. Here also the humming-bird finds food, 

 enabling it to continue through rain and snow, while within 10 

 degrees of latitude to the southward the snow is perpetual at 

 the waters' edge. 



The climatal effects of the contrary configuration are shown in 

 the Asiatic continent, where the extremes of heat and cold alter- 

 nately prevail in much lower latitudes than the southern point of 

 America, and where in the tropical and hypertropicai countries 

 there are substituted for these extremes the equally trying alter- 

 nations of extreme aridity and excessive moisture. It is true 

 that at the present day the effect of a trend of continent from 

 north to south, where it still occurs, does not, much as it modifies 

 the climate, present us with conditions analogous to those 

 afforded by the secondary period, as we cannot suppose that at 

 the extreme southern point of America reptiles such as existed 

 during the oolitic age could still exist. Nor is this to be ex- 

 pected, as allowance has to be made for the effect on terrestrial 

 climate produced by the numerous mountain chains of great 

 elevation which have come into existence since the secondary 

 period, to which in point of altitude we find no approximation 

 among the mountain chains of that period ; for even the Andes 

 (which during that period would seem to have been a chain of 

 volcanic islands) could not have had an altitude at all approaching 

 that which it has at present, since the secondary deposits now 

 occur in it at a considerable elevation. Allowance also should 

 be made for the effect on the temperature of the ocean, by the 

 increase in the depths corresponding to this increased altitude 

 of the mountains*. Besides this, we are not to lose sight of the 

 principle of the gradual refrigeration of climates in order of time, 

 however much it may have been interfered with by the distribu- 

 tion of land at different periods. 



The extension, however, of a great equatorial continent, such 

 as prevailed (as I have attempted to show) during the intra- 

 cretaceous and tertiary periods, must, I conceive, have brought 

 into existence a state of things the most opposite from that 

 which prevailed during the secondary period which it is conceiv- 

 able for geographical changes to produce. Continents upon 

 which occurred those extremes of heat and aridity, alternating 

 with excessive moisture, that are caused by the conversion of the 



* See the views of M. Boue upon the heights and depths during geolo- 

 gical periods, with his Table of them, in Bull. vol. xi. p. 62.^ 



