GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 317 



ON THE SUCCESSION OF THE SAME TYPES WITHIN THE SAME 

 AREAS, DURING THE LATER TERTIARY PERIODS 



Mr. Clift many years ago showed that the fossil mammals 

 from the Australian caves were closely allied to the living mar- 

 supials of that continent. In South America a similar relationship 

 is manifest, even to an uneducated eye, in the gigantic pieces of 

 armor, like those of the armadillo, found in several parts of La 

 Plata ; and Professor Owen has shown in the most striking manner 

 that most of the fossil mammals, buried there in such numbers, are 

 related to South American types. This relationship is even more 

 clearly seen in the wonderful collection of fossil bones made by 

 MM. Lund and Clausen in the caves of Brazil. I was so much 

 impressed with these facts that I strongly insisted, in 1839 and 

 1845, on this "law of the succession of types," — on "this wonder- 

 ful relationship in the same continent between the dead and the 

 living.'^ Professor Owen has subsequently extended the same 

 generalization to the mammals of the Old World. We see the same 

 law in this author's restorations of the extinct and gigantic birds 

 of New Zealand. We see it also in the birds of the caves of Brazil. 

 Mr. Woodward has shown that the same law holds good with 

 sea-shells, but, from the wide distribution of most mollusks, it is 

 not well displayed by them. Other cases could be added, as the 

 relation between the extinct and living land-shells of Madeira; 

 and between the extinct and living brackish-water shells of the 

 Aralo-Caspian Sea. 



Now, what does this remarkable law of the succession of the 

 same types within the same areas mean? He would be a bold man, 

 who, after comparing the present climate of Australia and of 

 parts of South America, under the same latitude, would attempt 

 to account, on the one hand through dissimilar physical conditions, 

 for the dissimilarity of the inhabitants of these two continents; 

 and, on the other hand through similarity of conditions, for the 

 uniformity of the same types in each continent during the later 

 tertiary periods. Nor can it be pretended that it is an immutable 

 law that marsupials should have been chiefly or solely produced 

 in Australia; or that Edentata and other American types should 

 have been solely produced in South America. For we know that 

 Europe in ancient times was peopled by numerous marsupials; 

 and I have shown, in the publications above alluded to, that in 

 America the law of distribution of terrestrial mammals was 

 formerly different from what it now is. North America formerly 



