188 



THE GEOLOGIST. 



even if they are positively identical, so long as they come from dif- 

 ferent formations they are classed by some palaeontologists as separate 



species. 



Migration too, must have played a very important part in the 

 sudden 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 country 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 light are intermediate to living forms, they seem to 

 my mind strong arguments in its favour. 



I have, then, taken for granted 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 differences that exist among organic forms. 



I have shown that there is no real ground for dissent, because we 

 have not yet found the missing connecting links, or because groups 

 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 

 wish any one to " mistake the scaffold 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 deterred from 

 (raining hypotheses and constructing theories, because we meet with 

 such dilemmas, and find ourselves frequently beyond our depths ? 

 Undoubtedly not."* 



This is the mystery 



Of this wonderful history, 



And the way to find it out. — Soutiiey. 



* Discourse on the study of Natural Philosophy, p. 19G. 



