22 ON THE LAW WHICH HAS REGULATED 
they differ considerably in their fossils, and you may 
then get some notion of how small a portion of the 
whole we know. 
But yet more important is the probability, nay 
almost the certainty, that whole formations contain- 
ing the records of vast geological periods are entirely 
buried beneath the ocean, and for ever beyond our 
reach. Most of the gaps in the geological series 
may thus be filled up, and vast numbers of un- 
Known and unimaginable animals, which might help 
to elucidate the affinities of the numerous isolated 
groups which are a perpetual puzzle to the zoologist, 
may there be buried, till future revolutions may 
raise them in their turn above the waters, to afford 
materials for the study of whatever race of intelli- 
gent beings may then have succeeded us. These con- 
siderations must lead us to the conclusion, that our 
knowledge of the whole series of the former inhabi- 
tants of the earth is necessarily most imperfect and 
fragmentary,—as much so as our knowledge of the 
present organic world would be, were we forced to 
make our collections and observations only in spots 
equally limited in area and in number with those 
actually laid open for the collection of fossils. Now, 
the hypothesis of Professor Forbes is essentially one 
that assumes to a great extent the completeness of 
our knowledge of the whole series of organic beings 
which have existed on the earth. This appears to 
be a fatal objection to it, independently of all other 
considerations. It may be said that the same ob- 
