FOSSIL FISH. 383 



bal, and accumulated in the greatest quantity ; as we find them, 

 for example, in the strata of Monte Bolca or Vestena Nuova. 



The traces which the fishes have left of their existence in the 

 bosom of the earth are very different in their nature. Rarely 

 enough do these consist of actual pieces of their skeleton ; 

 that is to say, the true fossils of this class are rare in nature. 

 For the most part they are nothing but impressions : the bones, 

 after having existed in the midst of the substance which has 

 enveloped them, becoming by degrees, in the long end, decom- 

 posed, have concluded by disappearing more or less com- 

 pletely. At other times, their impressions may have been 

 filled, so to speak, too late, and the fish appears in relief, or 

 very much compressed ; but nothing is seen but its external 

 form, or that of its scales, — nothing of the skeleton, properly 

 so called. 



It is rare to find fish in an isolated state, and especially so 

 in the coarse limestone ; where, nevertheless, the frequent pre- 

 sence of the calcareous osselets of the ear, proves that some 

 existed there when the waters of the sea washed the strata 

 where such remains are found. We may also conclude, that 

 as in the strata where there is no crystallization or petrifaction, 

 as at Grignon, no skeletons of fish are to be found, and yet 

 calcareous osselets are found, proving the existence of these 

 animals there formerly. Petrifaction has been necessary for 

 the preservation of the skeletons which the petrified strata 

 contain. 



Such fish as die naturally must become the food of other 

 fish, or of Crustacea ; so that we should not be surprised at not 

 finding them very often in the fossil state, in places where we 

 are assured that they must have existed in abundance. They 

 are more usually to be found, as we have seen, in great num- 

 bers, in one and the same locality, where they were evidently 

 destroyed by a volcanic eruption, or some other sudden and 

 violent catastrophe. At Monte Bolca, for instance, there can 

 be no sort of doubt that the revolution was sudden, and that 



