478 
SILUKIA. 
[Chap. XX. 
period in the history of the world wherein no vertebrated animal lived. 
In this sense, the appearance of the first recognizable fossil Fishes, to- 
wards the close of the Silurian period (and then they were cartilaginous 
and rare), seems to be as decisive a proof of a distinct creation as the 
placing of Man upon the terrestrial surface at the end of the long series 
of various animals which successively characterized the preceding geo- 
logical periods. 
Nor have we been able to disinter from the older strata charged with 
Invertebrata any distinct fragments of Land Plants. In the very same 
uppermost Silurian stratum, however, wherein the small early Fishes 
have been found, there also do we observe the first clear appearances of 
Trees. 
If it be granted that the position of the earliest recognizable Yertebrata 
is sound evidence on which to argue, still it may be contended that such 
forms may at a future period be found in still lower strata. In this 
work, however, I reason from known data only. Nor is it on such testi- 
mony alone, strong, clear, and universal as it is, that my argument is 
based ; for as soon as we pass into the formation immediately overlying, 
and quit the zone wherein the first few Fishes have been detected, we are 
furnished with collateral proofs that this was the earliest great step in a 
successive order of vertebrate creation which was never afterwards inter- 
rupted. In the following (or Devonian) period we are surrounded by a 
profusion of large fossil Fishes, with vertebrae sometimes ossified*, and with 
dermal skeletons of very singular forms, — all differing considerably from 
anything of their class in the succeeding epochs. It is thus clear that 
these Fishes were marked additions to the preexisting forms of marine life. 
Again, in this Devonian era we are presented with well-defined Land 
Plants, also of larger dimensions than the rare specimens in the uppermost 
Silurian. 
Just as the introduction of Cartilaginous Fishes is barely traceable to- 
wards the close of the long Silurian era, so, becoming afterwards much 
more abundant in the Devonian rocks, they are thenceforward abundantly 
associated in the Carboniferous and all younger formations with true 
Osseous Fishes and with Reptiles, the remains of which are found inter- 
mixed with the other products of the land and sea. 
Putting aside theory, therefore, and judging solely from observation, we 
fairly infer that during very long epochs the seas were unoccupied by 
Fishes, that the earliest discoverable creatures of this class had very 
rarely an osseous vertebral column, and, lastly, that in the succeeding 
period the Fishes having bony vertebrae appeared in greater numbers, and 
became ever afterwards abundant in the overlying deposits. Do not these 
absolute data of the geologist, resulting as they do from the most minute 
* A Coccosteus with true bony vertebrse has recently been found by Mr. C. Peach, and added to the 
Museum in Jermyn Street. 
