102 rHlLOSOPIIY OF ZOOLOGY'. 



duced on different species of animals, but little doubt need 

 be entertained that they were of considerable extent. 



In consequence of these changes which have taken place 

 on the earth's surface, corresponding alterations must have 

 been produced in its condition, as a residence for animals. 

 Every lake, as it was filled up, would receive the remains 

 of all those of its inhabitants, the locomotive powers of 

 which prevented them from shifting to a more suitable 

 dwelling. If a number of these lakes were filled up nearly 

 at the same time, over the whole, or a large portion, of the 

 globe, (and the universality of many of these upfilling for- 

 mations justify the supposition,) the total extinction of a 

 race of animals may have taken place ; and each succeeding 

 deposition may have been equally fatal to the surviving, 

 tribes. 



If every physical change which can take place on the 

 surface of the earth, whether it be an alteration of tempera- 

 ture, of the quantity of land or water, of moisture or dry- 

 ness, is detrimental to some animals, we need not be sur- 

 prised, that, amidst the vast number which has occurred, 

 many species have disappeared, whole races become extinct, 

 and the general features of the animal kingdom undergone 

 successive changes *. 



When we trace the characters of the different depositions 

 which have taken place from the newest alluvial beds to the 

 oldest transition rocks containing petrifactions, we witness 

 very remarkable gradations of character. The newest 



• Some conception may be formed of the effects of those changes which 

 have taken place on the earth's surface, on animals and vegetables, by ob- 

 serving the alterations which are produced by the drainage of a bog or lake. 

 Plants are destroyed, together with the'insects and shell-fish that fed on them. 

 Fish arc destroyed, and the worms on which they fed. The frog can no longer 

 find a fit place to deposit its eggs. The food of the water-fowl is destroyed, 

 and their haunts dried up. These ancient inhabitants are succeeded by 

 others suited to the new state of tiling?, — an emblem of the great revolutions 

 of the earth. 



