Chap. X.] PALiEONTOLOaiUAL COLLECTIONS. 271 



for ages in an unaltered condition. The remains which do become 

 embedded, 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 pre- 

 served. For instance, the several species of the Chthanialina? (a 

 sub-family of sessile cirripedes) coat the rocks all over the world in 

 infinite numbers : they aro all strictly littoral, with the exception 

 of a single Mediterranean species, which inhabits deep water, and 

 this has been found fossil in Sicily, whereas not one other species 

 has hitherto been found in any tertiary formation : yet it is known 

 that the genus Chthamalus existed during the Chalk period. Lastly, 

 many great deposits requiring a vast length of time for their accu- 

 mulation, are entirely destitute of organic remains, without our being 

 tible to assign any reason : one of the most striking instances is 

 that of the Flysch formation, which consists of shale and sandstone, 

 several thousand, occasionally even six thousand feet, in thickness, 

 and extending for at least 300 miles from Yienna to Switzerland ; 

 and although this great mass has been most carefully searched, no 

 fossils, except a few vegetable remains, have been found. 



With respect to the terrestrial productions which lived during 

 the Secondary and Palaeozoic periods, it is superfluous to state that 

 our evidence is fragmentary in an extreme degree. For instance, 

 until recently not a land shell was known belonging to either of 

 these vast periods, with the exception of one species discovered by 

 Sir C. Lyell and Dr. Dawson in the carboniferous strata of North 

 America; but now land-shells have been found in the lias. In 

 regard to mammiferous remains, a glance at the historical table 

 published in Lyell's Manual will bring home the truth, how acci- 

 dental and rare is their preservation, far better than pages of detail. 

 Nor is their rarity surprising, when we remember how large a pro- 

 portion of the bones of tertiary mammals have been discovered 

 either in caves or in lacustrine deposits ; and that not a cave or true 

 lacustrine bed is known belonging to the age of our secondary or 

 pakeozoic formations. 



But the imperfection in the geological record largely results 

 from another and more important cause than any of the foregoing ; 

 namely, from the several formations being separated from each 

 other by wide intervals of time. This doctrine has been empha- 

 tically admitted by many geologists and palaeontologists, who, like 

 E. Forbes, entirely disbelieve in the change of species. When we 

 see the formations tabulated in written works, or when we follow 

 them in nature, it is difficult to avoid believing that they are closel v 



