64 THE ORIGIN OF SPECIES 



tions are imperfect is admitted by every one. The 

 remark of that admirable paleontologist, Edward Forbes, 

 should never be forgotten, namely, that very many fossil 

 species are known and named from single and often 

 broken specimens, or from a few specimens collected on 

 some one spot. Only a small portion of the surface of 

 the earth has been geologically explored, and no part 

 "with sufficient care, as the important discoveries made 

 every year in Europe prove. No organism wholly soft 

 can be preserved. Shells and bones decay and disappear 

 when left on the bottom of the sea, where sediment is 

 not accumulating. We probably take a quite erroneous 

 view, when we assume that sediment is being deposited 

 over nearly the whole bed of the sea, at a rate suf- 

 ficiently quick to imbed and preserve fossil remains. 

 Throughout an enormously large proportion of the ocean, 

 the bright blue tint of the water bespeaks its purity. 

 The many cases on record of a formation conformably 

 covered, after an immense interval of time, by another \ 

 and later formation, without the underlying bed having 

 suffered in the interval any wear and tear, seem expli- 

 cable only on the view of the bottom of the sea not 

 rarely lying for ages in an unaltered condition. The re- 

 mains which do become imbedded, if in sand or gravel, 

 will, when the beds are upraised, generally be dissolved 

 by the percolation of rain-water charged with carbonic 

 acid. Some of the many kinds of animals which live 

 on the beach between high and low water mark seem to 

 be rarely preserved. For instance, the several species ofj 

 the Chthamalinse (a sub-family of sessile cirripeds) coat I 

 the rocks all over the world in infinite numbers: thevj 

 are all strictly littoral, with the exception of a single 



