320 THE POORNESS OF 



speaks its purity. The many cases on record of a forma- 

 tion conformably covered, after an immense interval of 

 time, by another and later formation, without the under- 

 lying bed having suffered in the interval any wear and tear, 

 seem explicable only on the view of the bottom of the sea 

 not rarely lying for ages in an unaltered condition. 

 The /emains 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 caibolic acid. Some of the many kinds of animals 

 which live on the beach between high and low water 

 mark scbni to be rarely preserved. For instance, the 

 several species of the Chthamalina3 (a sub-family of sessile 

 cirripedco) coat the rocks all over the world in intinite 

 numbers they are 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 for- 

 mation: yet it is known that the genus Olithamalus existed 

 during the Chalk period. Lastly, many great deposits, 

 requiring a vast length of time for their accumulation, are 

 entirely destitute of organic remains, without our being 

 able to assign any reason: one of the most striking in- 

 stances 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 Vienna to Switzerland; and although this 

 great mass has been most carefully searched, no fossils, 

 except a few vegetable remains, have been found. 



With resj^ect to the terrestrial productions which lived 

 during the Secondary and Palaeozoic periods, it is super- 

 fluous to state that our evidence is fragmentary in an 

 extreme degree. For instance, untill 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 marnmiferous remains, a glance at the histor- 

 ical table published in Lyell's Manual will bring home tlie 

 truth, how accidenral and rare is their preservation, f;i!- 

 better than pages of detail. Nor is their rarity surprisi ::,;•, 

 when we remember how large a proportion of the bones of 



