218 



THE WONDERS OF GEOLOGY. Lect. III. 



which it was placed.* In this point of view, fossil shells 

 become objects of the highest importance to the geologist, 

 since they are frequently the only indications of the circum- 



* There is, however, a source of error that cannot always be guarded 

 against : great changes are produced in shells by merely local influences, 

 and these are often mistaken for specific distinctions. Professor E. 

 Forbes, whose investigations have so beautifully elucidated many of the 

 phenomena relating to the submarine distribution of the mollusca, and 

 other aquatic animals, aflirms that many parts of the sea are too deep 

 to admit of the existence of any animals or vegetables ; and therefore, 

 that deposits of vast thickness, in which no organic remains can 

 occur, may be forming in those profound abysses at the present time. 



He remarks, that the absence of fossils in any marine stratum, is no 

 proof that when the bed was deposited, there might not have existed 

 above it a sea teeming with life. Now, admitting to the full extent the 

 facts and inferences adduced by this accomplished naturalist, in proof of 

 the intimate relation existing between the depth of water and the mine- 

 ral character of the sea-bottom, and the prevailing species and genera 

 of mollusca ; and entirely concurring in the opinion that the absence of 

 fossils in any strata, ought not to be admitted as proof that the waters 

 which deposited them were destitute of living things, yet I cannot 

 admit as a corollary from these premises, that very deep sea deposits 

 must necessarily be destitute of organic remains. The materials, 

 whether organic or inorganic, that are carried into the ocean by 

 streams and rivers, and the detritus of the cliffs and coasts trans- 

 ported by the powerful currents which traverse the entire area 

 of the ocean, and the sediments which accumulate in the most 

 profound abysses, may imbed organic remains, equally with those 

 which are deposited in shallower waters (see p. 70). With the 

 exception of those strata in which the local conditions prove that 

 the shells, corals, &c. lived and died on the areas where their remains 

 are imbedded, the prevalence or absence of fossil remains appears to 

 have principally depended on the influence of submarine currents, 

 tidal waves, &c. Nothing is more common than to find over vast 

 regions a like intermixture of shallow and deep-water species and 

 genera, — as rostellariae, turritelloe, melaniae, mussels, &c. collocated 

 with ammonites and nautili, fishes, radiaria, &c. that when living 

 inhabited geographical zones of very different depth : and this, too, 

 not only in littoral beds, but likewise in strata, which, from the 

 absence of gravel, sand, and other alluvial detritus (as in the white 

 chalk), we must infer to have been deep sea deposits. We have, then, 



