§60. CONCLUDING REMARKS. 291 



from internal sources, as explained by Sir J. Herschel and 

 Mr. Babbage, — may account for all the phenomena of this 

 nature, which our examination of the tertiary formations 

 has revealed. 



The occurrence of groups of animals of the same families, 

 in certain districts, is in strict conformity with the distribu- 

 tion of living species in regions not under the control of man. 

 Thus when ancient France presented a system of lakes, 

 animals fitted for such physical conditions found there the 

 means of subsistence — when the vast plains and forests of 

 America were adapted for colossal mammalia, there the 

 mastodon and the mammoth obtained food and shelter — and 

 when the former continent of Europe swarmed with herbi- 

 vora, the carnivorous tribes, as the lion, the tiger, and the 

 hyena, obtained the support which their habits and economy 

 required. 



One striking feature in the events that have passed in 

 review before us, is the immense scale on which the extinc- 

 tion of species and genera seems to have been effected : but 

 it must be remembered, that our observations have extended 

 over periods of vast duration, and that we have been con- 

 templating the aggregate effects of a law, which even in 

 modern times has produced, and is still producing, great 

 and important modifications in the system of animated 

 nature. In our attempts to penetrate the mystery which 

 veils the early scenes of the earth's physical history, by a 

 reference to the effects of the laws which now govern the 

 organic and inorganic kingdoms of nature, the caution of 

 the illustrious philosopher Playfair, should be ever present 

 to our minds : — " If existing causes appear to be inade- 

 quate to the effects produced, it may be only that, in respect 

 to man, their movements are too slow to be perceived. The 

 utmost portion of the progress to which human experience 

 can extend, is evanescent in comparison of the whole, and 

 must be regarded as the momentary increment of a vast 

 u2 



