IMPERFECTION OF GEOLOGICAL RECORD 65 



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, with- 

 out our being able to assign any reason: one of the most 

 striking instances is that of the Flysch formation, which 

 consists of shale and sandstone, several thousand, occa- 

 sionally even six thousand, feet in thickness, and extend- 

 ing 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 respect to the terrestrial productions which lived 

 during the Secondary and Paleozoic periods, it is super- 

 jQuous 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 peri- 

 ods, 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 accidental and rare is their 

 preservation, far better than pages of detail. Nor is 

 their rarity surprising, when we remember how large a 

 proportion 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 paleozoic formations. 



