7582 Notices of New Books. 



that the species of large genera, in each country, would oftener 

 present varieties than the species of the smaller genera ; for wherever 

 many closely-related species {i.e. species of the same genus) have 

 been formed, many varieties or incipient species ought, as a general 

 rule, to be now forming ; where many large trees grow, we may ex- 

 pect to find saplings ; where many species of a genus have been 

 formed, through variation, circumstances have been favourable to 

 variation, and hence we might expect that the circumstances might 

 still be favourable to variation. On the other hand, if we look at each 

 species as a special act of creation, there is no apparent reason why 

 more varieties should occur in a group having many species than in 

 one having few." 



From the gradations of affinity between the species of the suc- 

 cessive geological formations, more especially evident in the gradual 

 and even increase upwards in the proportion of existing to extinct 

 species of the tertiary deposits ; from the extinction of species never 

 to reappear, but to be replaced with an allied form more advanced in 

 organization ; from the progressive divergence in character between 

 recent members of a group, as compared with its species during the 

 geological period ; and from the geological succession of the same 

 types within the same geographical areas, implying the inherited 

 relationship of the successive species within those districts ; Mr. 

 Darwin implies the genealogical succession of organized beings 

 through the several geological periods, in preference to their being 

 the result of a series of distinct acts of creation. On this subject 

 Mr. Darwin says, at page 368 (third edition) : — "Mr. Clift, many 

 years ago, showed that the fossil mammals of the Australian caves 

 were closely allied to the living mammals of that continent. In 

 South America a similar relationship is manifest, even to an unedu- 

 cated 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 relationship is 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, in this law of the succession of types, — in this won- 

 derful relationship, on the same continent, between the dead and the 

 living. Professor Owen has subsequently extended the same gene- 

 ralizations 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 



