NATURAL SELECTION, ETC. 113 



course of time, so that one species may at length be 

 naturally replaced by another species a good deal like 

 it, or may be diversified into two, three, or more 

 species, or forms as different as species. This con- 

 cedes all that Darwin has a right to ask, all that he 

 can directly infer from evidence. We must add that 

 it affords a locus standi, more or less tenable, for in- 

 ferring more. 



Here another geological consideration comes in to 

 help on this inference. The species of the later ter- 

 tiary period for the most part not only resembled 

 those of our days — many of them so closely as to sug- 

 gest an absolute continuity — but also occupied in gen- 

 eral the same regions that their relatives occupy now. 

 The same may be said, though less specially, of the 

 earlier tertiary and of the later secondary; but there 

 is less and less localization of forms as we recede, yet 

 some localization even in palseozoic times. "While in 

 the secondary period one is struck with the similarity 

 of forms and the identity of many of the species 

 which flourished apparently at the same time in all or 

 in the most widely-separated parts of the world, in 

 the tertiary epoch, on the contrary, along with the 

 increasing specialization of climates and their approxi- 

 mation to the present state, we find abundant evi- 

 dence of increasing localization of orders, genera, and 

 species ; and this localization strikingly accords with 

 the present geographical distribution of the same 

 groups of species. "Where the imputed forefathers 

 lived, their relatives and supposed descendants now 

 flourish. All the actual classes of the animal and 

 vegetable kingdoms were represented in the tertiary 



