He, 



lo 



;i 



:0 



7 



e 



an. 



•erfiii 



J", at 



»ecies 

 wies 

 "as a 

 itliin 



> • 



L 5 



-?nl 



iiost 



■nof 



on; 



[lies 



the 



•nis 



ire 



or 



r 



i 



f 



Ch. xlii.] concluding eemarks on extinction. 



463 



their existence in the crnst of the earth. In Chapter XIV. 

 I have treated of the fragmentary natnre of the geological 

 record^"^ re-affirming what I first stated in 1833, that it is 

 scarcely possible to exaggerate the defectiveness of our 

 archives. These records, like the existing species, are con- 

 stantly v^asting away before onr eyes, while neiv deposits, 

 containing the partial memorials of the modern fauna and 

 flora, are now in the process of formation. But as the new 

 strata are deposited out of sight, chiefly in the basins of seas 



and lakes, their 



origin is not so 



conspicuous as is the de- 



struction of the memorials of older date. 



So alsO; as before stated (p. 269), the dying out of old forms is 

 more easily proved than the coming in of new ones. We might 

 see in a large forest a fuU-groAvn tree blown down or felled by 

 the axe every day in the year, and yet at the end of fifty years 

 find that the number and size of the trees in the forest was 

 the same as before, because the daily growth of timber spread 

 over many thousands of trees, though insensible to the eye, 

 may every day produce a quantity of foliage and timber equal 

 in the aggregate to that contained in a single full-grown 

 tree. 



before hinted (p. 272), the loss may be compensated bj 

 the amount of permanent change effected by Yariation and 

 Natural Selection, in the course of a single year, among 

 thousands of species. 



In like manner, if one species die out annually, as 



* Vol. I. pp. 317-320. 



1 



f 



s 



56 



le 



