188 
THE GEOLOGIST. 
even if they are positively identical, so long as they come from dif- 
ferent formations they are classed by some paleontologists as separate 
species. 
Mio-ration too, must have played a very important part in the 
sudde'n appearance of species. And with regard to the first appear- 
ance of life, if even any of the remains of the oldest fossiliferous 
formation should still exist in that quarter of the globe which we can 
alone examine, it seems to me, when I think of the very small extent 
of countiy that has been geologically explored, extremely rash to 
infer that we have already found them. 
When we take all these things into consideration we can, I think, 
easily account for groups of species coming apparently into the 
world at once ; and that owing to the extreme imperfection of the 
geological record, we cannot ever expect to find all or most of the 
connecting links between species, or even feel surprised at their being 
absent. I therefore see no reason for disbelieving the theory on 
geological grounds ; on the contrary, as we find that all the fossils 
yet brought to Hght are intermediate to hving forms, they seem to 
my mind strong arguments in its favour. 
I have, then, taken for gi'anted that species vary, and have shown 
that not only has no limit been put as yet to that variation, but that 
the weight of the evidence is in favour of its extension. 
I have taken for granted that natural selection is a " vera causa," 
and have, I think, shown that it is sufficiently powerful to produce 
the greatest difierences that exist among organic forms. 
I have sho^Ti that there is no real ground for dissent, because we 
have not yet found the missing connecting links, or because gi'oups 
of species appear suddenly ; but that on the contrary the geological 
argument is in its favour. 
Therefore when we see that we can explain, by the transmutation 
of one species into another, nearly all the facts in the science of 
biology, we are, I think, entitled to look upon it as a very probable 
hypothesis — more probable than any other yet brought forward — and 
one that, by the clear and comprehensive views it gives of organic life, 
will lead to great discoveries. I do not wish to go further. I do not 
^^ish any one to " mistake the scafibld for the pile." I know that it 
rests at present on presumptive evidence alone, and that there are 
many " dilemmas" to be overcome before it can be accepted as true ; 
but, in the words of Sir John Herschel, " are we to be deteiTed from 
framing hypotheses and constructing theories, because avc meet with 
such dilemmas, and find ourselves frequently beyond oui' depths ? 
Undoubtedly not."* 
This is the mystery 
Of this wonderful history, 
And the way to find it out. — Southey. 
* Discourse on the study of ISTatui-al Philosophy, p. 196. 
