SUCCESSION OF SAME TYPES 389 



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 distribution of most molluscs, it is not well 

 displayed by them. Other cases could be added, as the rela- 

 tion 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 Aus- 

 tralia and of parts of South America, under the same lati- 

 tude, 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 mar- 

 supials; 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 partook strongly of the present character 

 of the southern half of the continent; and the southern half • 

 was formerly more closely allied, than it is at present, to the 

 northern half. In a similar manner we know, from Falconer 

 and Cautley's discoveries, that Northern India was formerly- 

 more closely related in its mammals to Africa than it is at 

 the present time. Analogous facts could be given in rela- 

 tion to the distribution of marine animals. 



