306 
IMPEEFECTION OF THE 
Chap. IX. 
much older fishes, of which the affinities are as yet 
imperfectly known, are really teleostean. Assuming, 
however, that the whole of them did appear, as Agas¬ 
siz believes, at the commencement of the chalk forma¬ 
tion, the fact would certainly be highly remarkable; 
but I cannot see that it would be an insuperable diffi¬ 
culty on my theory, unless it could likewise be shown 
that the species of this group appeared suddenly and 
simultaneously throughout the world at this same pe¬ 
riod. It is almost superfluous to remark that hardly 
any fossil-fish are known from south of the equator; 
and by running through Pictet’s Palaeontology it will 
be seen that very few species are known from several 
formations in Europe. Some few families of fish now 
have a confined range ; the teleostean fish might for¬ 
merly have had a similarly confined range, and after 
having been largely developed in some one sea, might 
have spread widely. Nor have we any right to sup¬ 
pose that the seas of the world have always been so 
freely open from south to north as they are at present. 
Even at this day, if the Malay Archipelago were con¬ 
verted into land, the tropical parts of the Indian Ocean 
would form a large and perfectly enclosed basin, in 
which any great group of marine animals might be 
multiplied; and here they would remain confined, until 
some of the species became adapted to a cooler climate, 
and were enabled to double the southei’n capes of Africa 
or Australia, and thus reach other and distant seas. 
From these and similar considerations, but chiefly 
from our ignorance of the geology of other countries 
beyond the confines of Europe and the United States; 
and from the revolution in our palaeontological ideas 
on many points, which the discoveries of even the last 
dozen years have effected, it seems to me to be about 
as rash in us to dogmatize on the succession of organic 
