NEW SCIENCE OF PALEONTOLOGY 



in the animate creation. If we divide the surface of 

 the earth into twenty regions of equal area, one of 

 these might comprehend a space of land and water 

 about equal in dimensions to Europe, and might con- 

 tain a twentieth part of the million of species which 

 may be assumed to exist in the animal kingdom. In 

 this region one species only could, according to the rate 

 of mortality before assumed, perish in twenty years, 

 or only five out of fifty thousand in the course of a cen- 

 tury. But as a considerable portion of the whole 

 world belongs to the aquatic classes, with which we 

 have a very imperfect acquaintance, we must exclude 

 them from our consideration, and, if they constitute 

 half of the entire number, then one species only might 

 be lost in forty years among the terrestrial tribes. 

 Now the mammalia, whether terrestrial or aquatic, 

 bear so small a proportion to other classes of animals, 

 forming less, perhaps, than a thousandth part of a 

 whole, that, if the longevity of species in the different 

 orders were equal, a vast period must elapse before it 

 would come to the turn of this conspicuous class to 

 lose one of their number. If one species only of the 

 whole animal kingdom died out in forty years, no 

 more than one mammifer might disappear in forty 

 thousand years, in a region of the dimensions of Eu- 

 rope. 



44 It is easy, therefore, to see that in a small portion 

 of such an area, in countries, for example, of the 

 size of England and France, periods of much greater 

 duration must elapse before it would be possible to 

 authenticate the first appearance of one of the larger 

 plants or animals, assuming the annual birth and death 



