Appendix to Chapter V. 423 



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 palaeozoic formations." 



But perhaps of even more importance than all these known 

 causes which prevent the formation of fossils, is the existence 

 of unknown causes which make for the same result. For 

 example, the Flysch-formation is a formation of several 

 thousand feet in thickness (as much as 6000 in some places), 

 and it extends for at least 300 miles from Vienna to 

 Switzerland ; moreover, it consists of shale and sandstone. 

 Therefore, alike in respect of time, space, and character, it is 

 just such a formation as we should expect to find highly rich 

 in fossils; yet, "although this great mass has been most 

 carefully searched, no fossils, except a few vegetable remains, 

 have been found." 



So much then for the difficulty, so to speak, which nature 

 experiences in the manufacture of fossils. Probably not one 

 per cent, of the species of animals which have inhabited the 

 earth has left a single individual as a fossil, whereby to record 

 its past existence. 



But of even more importance than this difficulty of making 

 fossils in the first instance, is the difficulty of preserving them 

 when they are made. The vast majority of fossils have been 

 formed under water, and a large proportional number of 

 these whether the animals were marine, terrestrial, or 

 inhabitants of fresh water have been formed in sedimentary 

 deposits either of sand, gravel, or other porous material. 

 Now. where such deposits have been afterwards raised into 

 the air for any considerable time and this has been more or 

 less the case with all deposits which are available for explora- 

 tion their fossiliferous contents will have been, as a general 

 rule, dissolved by the percolation of rain-water charged with 

 carbonic acid. Similarly, sea-water has recently been found 

 to be a surprisingly strong solvent of calcareous material: 

 hence, Saturn-like, the ocean devours her own pio&eny 



