ix.] PALAEONTOLOGY AND EVOLUTION. 201 



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 relationship 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 connection with the earlier labours of our 

 lamented colleague Falconer ; and it has been instruc- 

 tively discussed in the thoughtful and ingenious work of 

 Mr. Andrew Murray " On the Geographical Distribution 

 of Mammals." l 



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 imme- 

 diate consequences clearly is, that the present distribu- 

 tion 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 immi- 

 gration of living forms from some other area. 



1 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. 



