DISTRIBUTION. 327 



some records remain : cannot extend to those pre-geologic 

 times the records of which haye been obliterated. From 

 these remaining records, which probably form but a small 

 fraction of the whole, the general facts deducible are : — That 

 snch organic types as have lived through successive epochs, 

 have almost universally undergone modifications of specific 

 and generic values — modifications which have commonly been 

 great in proportion as the period has been long. That besides 

 the types that have persisted from ancient eras down to our 

 own era, other types have from time to time made their ap- 

 pearance in the ascending series of our strata — types of which 

 some are lower and some higher than the types previously 

 recorded ; but whence these new types came, and whether 

 any of them arose by divergence from the previously-recorded 

 types, the evidence does not yet enable us to say. That in 

 the course of long geologic epochs, nearly all species, most 

 gerera, and a few orders, become extinct ; and that a species, 

 genus, or order, which has once disappeared from the Earth, 

 never reappears. And, lastly, that the Fauna now occupying 

 each separate area of the Earth's surface, is very nearly allied 

 to the Fauna which existed on that area during recent geolo 

 gic times. 



§ 108. Omitting sundry minor generalizations, the exposi- 

 tion of which would involve too much detail, what is to be 

 said of these major generalizations ? 



The distribution in Space cannot be said to imply that or- 

 ganisms have been designed for their particular habitats, and 

 placed in them ; since, besides the habitat in which an organ- 

 ism is found there are commonly other habitats, as well or 

 better for it, from which it is absent — habitats to which it 

 is so much better fitted than organisms now occupying them, 

 that it extrudes these organisms when allowed the oppor- 

 tunity. Neither can we suppose that one end has been to 

 establish varieties of Floras and Faunas ; since, if so, why are 

 the Floras and Faunas but little divergent in widely-sundered 



