484 
SILURIA. 
[Chap. XX. 
earths crust have been mainly directed to those Tertiary rocks in which, 
for the first time, in mounting from older to newer strata, we meet with a 
great variety and profusion of Mammals, of all sorts and sizes, many of 
them, indeed, still being the associates of Man. In such Tertiary forma- 
tions, we have, indeed, before us on all sides the bones of the higher orders 
of Mammalia, drifted from numerous adjacent lands, and associated with 
the exuviae of marine creatures, which, though scarcely more abundant 
than those of the earlier formations, are all of different species. 
Animals, in short, of every class, whether terrestrial or marine, and 
particularly Mammalia, abound more and more in each succeeding forma- 
tion of Tertiary age, exhibiting an increasing quantity and variety of both 
sea and land creatures as we approach the superficial accumulations. In 
these only are entombed the bones of such gigantic mammals as the Mam- 
moth, — quadrupeds which once inhabited our present continents, and which 
must have required for their sustenance a range over lands probably as ex- 
tensive as those occupied by Man and his associates. Of Man we have no 
traces until after the Glacial Period, or the last of the great physical changes 
before the present configuration of the earth's outlines was determined. 
Let the reader dwell on these remarkable facts which the close labours 
of geologists have elicited in this century. Let him view them in the clear 
and broad order indicated by Nature, advancing from an Invertebrate to a 
Vertebrate era, and next mark a regular rise thenceforward in the numbers 
and organization of animals by the addition, in successive epochs, first of 
Eeptiles and then of Mammals. Let him execute a patient survey from 
the lower deposits upwards, and he will find everywhere a succession of 
creatures rising from lower to higher organizations, — a doctrine promul- 
gated by the illustrious Cuvier, but from infinitely less perfect data than 
we now possess *. 
Yet, however they admit the facts, some of my cotemporaries think 
that they can so explain them as to reject a belief in successive creations 
from lower to higher classes. They suppose that nearly all the strata of 
date antecedent to those in which the first signs of life have been detected 
are often in so crystalline a state that, if they originally contained remains 
of animals, the traces of them must have been obliterated by changes since 
effected in the structure of the rock. Now, if this supposition had been' 
supported by the researches of late years, we must doubtless have admitted 
that all evidence of the earliest creation has been buried in a hopeless 
obscurity ; but this difficulty (which I never underrated) has been quite 
set aside by the discovery of the Eozoon in those highly crystalline rocks 
which form the basement of every known formation. Then, again, above 
these fundamental strata we find, as before explained, deposits many 
* The Palaeozoic or primeval fossils were neces- the higher orders of Vertebrata which appear in 
sarily little known to that great comparative ana- the more recent epochs only, and specially those 
tomist, who drew his conclusions from data within of the Paris Basin, 
the scope of the knowledge of his day, i. e. from 
