240 THE DOCTRINE OF DESCENT. 



that SO early as the Jurassic era, the northern hemisphere 

 was peopled by Marsupials, but, it is evident, not densely. 

 We must suppose that, retaining their character, the Mar- 

 supials of the southern continent tested and proved their 

 powers of adaptation, whereas on the other side of the 

 equator a race of mammals of completely different cast 

 proceeded from them. This is the race which still char- 

 acterizes the whole surface of the earth from the north 

 to the point of contact with the more stable remnants 

 of antarctic life. While with reference to their origin we 

 can appeal only to reason and inference, the historical 

 connection between the mammalia now peopling the Old 

 and the greater part of the New World, and their pred- 

 ecessors up to the most ancient Tertiary periods, is 

 manifest to our eyes. 



The remains of the earliest mammals here to be con- 

 sidered, are found in the Eocene deposits of Switzerland, 

 and in corresponding strata in France and the south of 

 England. From the southern edge of the Jurassic 

 plateau, neither the Alps nor any other land was visible, 

 and the ocean which washed its shores has been traced 

 as far as China. The mammaHa of this period, as far as 

 they are known, amount, according to the synopsis made 

 by Riitimeyer in 1867, to at least 70 species. The ma- 

 jority are ungulate, therefore Graminivora; of these, by 

 far the greater number Pachydermata. Now, when the 

 entire world scarcely maintains so many Pachyderms, 

 the proportions are quite altered. In Europe, the pig 

 alone represents this division, and Ruminants everywhere 

 predominate. In its present animal population, Africa 

 might be approximately compared to Eocene Europe. 

 But as to these Ungulates must be added a large num- 



