Chap. X. SAME TYPES IN SAME AREAS. 339 



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 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 won- 

 derful relationship in the same continent between the 

 dead and the living." Professor Owen has subsequently 

 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 distribu- 

 tion 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 succes- 

 sion of the same types within the same areas mean ? 

 He would be a bold man, who after comparing the pre- 

 sent 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, 



Q 2 



