hunter's posthumous paper on fossils. 815 



Monte Bolca, and of the Permian schists of Eislehen, is the different 

 structure and composition of the scales of the extinct fishes of those two 

 remote geological periods. In the earlier (Permian) period the fishes 

 were ' ganoid/ or had bony and enamelled scales which became petrified : 

 in the later tertiary period the fishes were ' cycloid' or ' ctenoid,' i. e. 

 had flexible and soluble scales like those of most osseous fishes of the 

 present period. With the better dermal ossification of the older fishes 

 was usually associated a less complete ossification of the endo -skeleton, 

 and the reverse in the later fishes ; all which circumstances combine to 

 make the evidences of ' secondary' fishes to be chiefly scales, and those 

 of ' tertiary' fishes chiefly skeletons. 



Hunter divides fossils into three kinds : first, fossils proper, having as a 

 basis the earth of bones and shells, retaining their shape, though not 

 always their texture ; secondly, ' casts ;' and thirdly, ' moulds.' " What 

 are called ' vegetable fossils' are no more than either a change of matter, 

 or a cast ; and in leaves or soft vegetables there is nothing but the 

 mould, the two sides of which are in contact, as if pressed together 

 after the impression had been made and the vegetable destroyed." — 

 P. xxxi. 



" Another species of fossil is a gradual decomposition, and a new 

 deposit; where the whole parts originally composing the bone have 

 been removed, and an earth of some kind deposited in its place, keep- 

 ing up all the same structure and arrangements as in the original bone. 

 That this is the case must be evident, as there is not a single grain of 

 calcareous substance in the whole composition." — P. xxxiii. 



" We find the cavity formed by the two valves [of a bivalve shell] 

 often filled with different earth ; frequently very beautiful crystalliza- 

 tion in it ; the same in the univalves, and, which is very common in 

 the Nautilus and Cornu Ammonis, their cavities being not easily filled 

 with gross matter. Some have, in the place of the shell, constantly a 

 east of a peculiar crystallization forming calcareous spar, such as the 

 Echinus, the Encrinus, and probably all of the star-fish kind, which 

 would seem to have been decomposed, and a new mode of crystallization 

 has taken place. Their structure in the fossil state is certainly not 

 similar to the natural. It would appear that the original had hardly 

 sufficient calcareous matter to form such crystallization, though probably 

 not new matter. Such are often found in chalk, and filled with the 

 same, or are imbedded, as also filled with a siliceous matter from a pale 

 to a black flint." — P. xxxiv. 



" The sea has afforded the truest fossils, and the greatest number : 

 .... Pavers," Hunter proceeds to say, " carry into the sea various 

 earthy matters either mechanically mixed or in solution, which matters 



