438 FOSSIL INVERTEBRATED ANIMALS. 



In disappearing from other strata, as well as the chalk, the 

 testaceous covering of the mollusca has left the mould of its 

 forms, both internal and external. This mould is so exact, that 

 it represents, in all its parts, the lines, the striae, or the slightest 

 asperities, which belonged to the original production. Such of 

 these moulds, as derive their origin from the animal kingdom, 

 have been called helm i nth olites, entomolites, ichthyolites, 

 amphibiolites, ornitholites, zoolites ; such as are derived from 

 the vegetable kingdom are named phytolites. 



The external moulds being entire, and often without the 

 slightest fracture, the testae on which they have been found 

 cannot possibly have left them in any other way than by solu- 

 tion, after the soft matter, in which they were imbedded, had 

 undergone a crystallization or petrifaction, which thus preserved 

 all the communicated forms. 



In certain strata, such as that of the Mount St. Pierre of 

 Maestricht, for example, we find that some external moulds of 

 univalve shells are filled, only through one-half of their length, 

 with a substance similar to that of the stratum, as if this sub- 

 stance had not been in sufficient quantity to fill the entire 

 mould. We cannot, however, be certified that this was the 

 case, since we see that, in these external moulds, there remain 

 very well-formed portions of the internal mould. It seems 

 more reasonable to attribute the cause of this singular fact to 

 a partial solution of the latter, after the formation of these im- 

 pressions. 



Although we are unacquainted, at the present day, with any 

 agent capable of producing a similar dissolution, without also 

 attacking the calcareous mould which surrounds these bodies, 

 still we cannot attribute their disappearance to any other cause 

 than the action of the waters, and other fluids, which are con- 

 tinually traversing the earth, from its surface to its profoundest 

 abysses. 



If the waters have the power of dissolving the calcareous 



