EXTERMINATION OF ANIMALS. 183 



conclusion, that there ever has been, and is still going on, u gradual and 

 regular change in the earth's polarity, and consequently in its tempera- 

 ture. The author of the " Menageries," when speaking of fossil bones, 

 observes, that though it has been usual to refer the destruction of the 

 animals to which they belong to the great Deluge, yet " it does not in 

 the least invalidate the authority of the sacred books to believe that 

 other causes of the destruction of life may have been called into action, 

 previously to, or simultaneously with, that great event, of which so 

 many undoubted traces may be found. A very general belief now 

 prevails amongst geologists, that the climate of the northern hemi- 

 sphere has undergone an important change, and that its mean annual 

 temperature must once have resembled that now experienced within 

 the tropics.* Shells and corals, having an affinity with species now 

 living in warmer latitudes; remains of reptiles belonging to hot cli- 

 mates, such as turtles, tortoises, and crocodiles; fossil plants, such as 

 palms of the most luxuriant growth, which could only have been pro- 

 duced under the influence of high temperature; and, above all, the 

 bones of the quadrupeds of the tropics: all these, which have been 

 found in such abundance in Europe, have naturally pointed out that a 

 great change of this nature must have taken place." The same writer 

 remarks, that, " the theory of a slow change of temperature produced 

 by the new formation of great masses of land, has derived considerable 

 support from the well-known facts connected with the remains of the 

 Siberian elephants." Some excellent remarks upon this subject are 

 made by Mr. Lyell, who considers it fair to infer, that " the same 

 change of climate which has caused certain Indian species of testacea to 

 become rare, or to degenerate in size, or to disappear from the Mediter- 

 ranean, and certain genera of the sub-appenine hills, now exclusively 

 tropical, to retain no longer any representatives in the adjoining seas, 

 has also contributed to the annihilation of certain genera of land mam- 

 mifera, which inhabited the continent at about the same epoch. The 

 mammoth (Elephas primigenus), and other extinct animals of the 

 same era, may not have required the same temperature as their living 

 congeners within the tropics : but we may infer that the climate was 

 milder than that now experienced in some of the regions once inhabited 

 by them, because in Northern Russia, where their bones are found in 

 immense numbers, it would be difficult, if not impossible, for such ani- 

 mals to obtain subsistence, at present, during an arctic winter. It has 



* Lyell's Geology, vol. i. p. 92. 



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