304 ON THE ORIGIN OF SPECIES 



On the Succession of the same Types within the same 

 areas, during the later tertiary periods. — Mr. Clift many 

 years ago snowed 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 armour like those of the arma- 

 dillo, 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 relation- 

 ship is even more clearly seen in the wonderful collec- 

 tion 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 

 wonderful relationship in the same continent between 

 the dead and the living." Professor Owen has subse- 

 quently extended the same generalisation 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 genera of molluscs, 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, by dissimilar physical conditions for the 

 dissimilarity of the inhabitants of these two continents, 

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

 the uniformity of the same types in each during the 

 later tertiary periods. Nor can it be pretended that it 

 is an immutable law that marsupials should have been 



