ANNIVERSARY ADDRESS TO THE GEOLOGICAL SOCIETY 521 
the successive populations of the globe, which so many seem to think 
are already answered. 
The preceding arguments make no particularclaim to novelty ; 
indeed they have been floating more or less distinctly before the 
minds of geologists for the last thirty years; and if, at the present 
time, it has seemed desirable to give them more definite and system- 
atic expression, it is because paleontology is every day assuming 
a greater importance, and now requires to rest on a basis whose 
firmness is thoroughly well assured. Among its fundamental con- 
ceptions, there must be no confusion between what is certain and 
what is more or less probable.’ But, pending the construction of 
a surer foundation than paleontology now possesses, it may be in- 
structive, assuming for the nonce the general correctness of the 
ordinary hypothesis of geological contemporaneity, to consider 
whether the deductions which are ordinarily drawn from the whole 
body of paleontological facts are justifiable. 
The evidence on which such conclusions are based is of two 
kinds, negative and positive. The value of negative evidence, in 
connexion with this inquiry, has been so fully and clearly discussed 
in an address from the chair of this Society,? which none of us have 
forgotten, that nothing need at present be said about it; the more 
as the considerations which have been laid before you have certainly 
not tended to increase your estimation of such evidence. It will 
be preferable to turn to the positive facts of paleontology, and to 
inquire what they tell us. 
We are all accustomed to speak of the number and the extent of 
the changes in the living population of the globe during geological 
time as something enormous ; and indeed they are so, if we regard 
only the negative differences which separate the older rocks from the 
more modern, and if we look upon specific and generic changes as 
great changes, which from one point of view they truly are. But 
leaving the negative differences out of consideration, and looking 
only at the positive data furnished by the fossil world from a broader 
point of view—from that of the comparative anatomist who has 
made the study of the greater modifications of animal form his chief 
business—a surprise of another kind dawns upon the mind; and 
under this aspect the smallness of the total change becomes as 
astonishing as was its greatness under the other. 
1 Le plus grand service qu’on puisse rendre a la science est d’y faire place nette avant 
d’y rien construire.” — Cuvier. 
2 Anniversary Address for 1851, Quart. Journ. Geol. Soc. vol. vil. 
