liv PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
But the growth of knowledge in the interval makes me conscious 
of an omission of considerable moment in that statement, inasmuch 
as it contains no reference to the bearings of paleontology upon the 
theory of the distribution of life; nor takes note of the remarkable 
manner in which the facts of distribution, in present and past 
times, accord with the doctrine of evolution, especially in regard to 
land animals. 
That connexion between paleontology and geology on the one 
hand, and the present distribution of terrestrial animals, which so 
strikingly impressed Mr. Darwin thirty years ago as to lead him to 
speak of a “law of succession of types,” and of the wonderful rela- 
ionship on the same continent between the dead and the living, 
has recently received much elucidation from the researches of 
Gaudry, of Riitimeyer, of Leidy, and of Alphonse Milne-Edwards, 
taken in connexion with the earlier labours of our lamented col- 
league Falconer; and it has been instructively discussed in the 
thoughtful and ingenious work of Mr. Andrew Murray ‘On the 
Geographical Distribution of Mammals’*. 
I propose to lay before you, as briefly as I can, the ideas to which 
a long consideration of the subject has given rise in my own mind. 
If the doctrine of evolution is sound, one of its immediate con- 
sequences clearly is, that the present distribution of life upon the 
globe is the product of two factors, the one being the distribution 
which obtained in the immediately preceding epoch, and the other 
the character and the extent of the changes which have taken place 
in physical geography between the one epoch and the other; or, to 
put the matter in another way, the Fauna and Flora of any given 
area, in any given epoch, can consist only of such forms of life as 
are directly descended from those which constituted the Fauna and 
Flora of the same area in the immediately preceding epoch, unless 
the physical geography (under which I include climatal conditions) 
of the area has been so altered as to give rise to immigration of 
living forms from some other area. 
The evolutionist, therefore, is bound to grapple with the following 
problem whenever it is clearly put before him :—Here are the Faunz 
of the same area during successive epochs. Show good cause for 
believing either that these Faunz have been derived trom one 
another by gradual modification, or that the Faune have reached the 
area in question by migration from some area in which they have 
undergone their development. 
I propose to attempt to deal with this problem, so far as it is ex- 
emplified by the distribution of the terrestrial Vertebrata, and I 
shall endeavour to show you that it is capable of solution in a sense 
entirely favourable to the doctrine of evolution. 
* The paper “On the Form and Distribution of the Land-tracts during the 
Secondary and Tertiary periods respectively; and on the effect upon Animal 
Life which great changes in Geographical Configuration have probably pro- 
duced,” by Mr. Searles V. Wood, Jun., which was published in the ‘ Philoso- 
phical Magazine’ in 1862, was unknown to me when this Address was written. 
It is well worthy of the most careful study. 
