CAMBRIDGE ESSAYS : HOPKINS* "GEOLOGY." 
517 
Geological Society in 1851, and to the review of it shortly after in the 
"Quarterly Eeview." 
The subject will, however, be better presented to the minds of most 
of our readers through the medium of general facts. According to 
existing evidence it appears that invertebrate animals alone existed in 
the earlier palEeozoic period. Pishes were then introduced and existed 
in great numbers in the Devonian period ; and shortly afterwards 
reptiles appeared. Small mammals existed in the Middle or Mesozoic 
period, the whole class becoming completely developed only in the 
latest geological era. The remains of birds, as might be expected, are 
comparatively very rare. The introduction of man is the great and 
final step in this progressive series. 
These facts, and numerous others, are calculated to refute both the ex- 
ti'eme theories before mentioned — that of the complete development of 
organic life by successive steps, from the lowest and simplest forms to 
the highest and most complicated, terminating in man ; and that which 
maintains that there has been no progression at all. 
But because the proof of one theory is imperfect, we are not there- 
fore to reject it wholly because of the incompleteness of the proof. 
We have a large amount of positive evidence in favour of progression ; 
on the other hand, we are not aware of any positive evidence whatever 
in favour of non-progression, and we are called upon by its advocates 
to believe it, because future discoveries may supply such evidence. 
Mr. Hopkins now discusses the question. How were new species of 
animals originally introduced on the face of our globe ? and inclines to 
the opinion that their introduction was distinct from any progressive 
transmutation of species according to any actual law of nature, and 
consequently supernatural. 
Geoffrey St. Hilaire, at the close of the last century, was one of the 
earliest leaders of the school of transcendental anatomy, as it has been 
termed. In his views St. Hilaire was directly opposed to the great 
Cuvier himself, whose labours assuredly laid the foundation of that 
branch of palaeontology which relates to the vertebrata, and which has 
been since so successfully prosecuted by his successors, and by none 
more so than our distinguished countryman, Professor Owen. 
With the advance of knowledge of animal organziation, speculative 
naturalists began to search for generalizations of a higher order than 
those of mere zoological classification, and many of them adopted the 
principle of a unitij of plan pervading the entire range of animal organ- 
ization. The poet Goethe was one of the first who entered into these 
speculative views, which resolved themselves practically into endeavours 
to discover a form which should serve as a type of all organic forms in 
the animal kingdom, according to the fundamental notion of a unity of 
plan, and this object was restricted for a time to the vertebrate skeleton. 
In the vertebrata the persevering researches of distinguished naturalists 
have been crowned, it is considered, with success, although they are 
still far from being agreed as to the precise typical form. That pro- 
posed by Professor Owen — a naturalist possessed of the boldness of this 
school of trancendentalists, tempered by the true spirit of induc- 
tive philosophy — being regarded as having the strongest claims to 
confidence. 
