2.|0 THE DOCTRINE OF DESCENT. 



know 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 Marsupials of the southern continent 

 tested and proved their powers of adaptation, whereas 

 on the other side of the equator a race of mammals cf 

 completely different cast proceeded from them. This is 

 the race which still characterizes 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 predecessors 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 mammalia 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 

 majority 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. Ln its present animal population, Africa 

 might be approximately compared to Eocene Europe. 

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



