240 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 of 
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, 
this ratio is quite disproportionate. 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- 
