436 FOSSIL INVERTEBRATED ANIMALS. 



peared ? This conjecture is corroborated by the almost positive 

 certainty that a great number have been dissolved in the supe- 

 rior chalk without leaving any traces behind. Moreover, the 

 trilobites, and other turbinated bodies, which are found in the 

 aforesaid depositions, lived on animals, and probably on testa- 

 ceous animals — the traces of which would be found, had they 

 not been dissolved or destroyed in the course of the time in 

 which the schistose phyllades were being formed. 



It is probable that the absence or presence of organic bodies 

 in the strata of the phyllades, has occasioned certain of these 

 depositions to be ranked among primitive substances, and others 

 to be considered as intermediate ; for the superposition of the 

 primitive rocks can no longer be a guide in this case, since the 

 example of the granite of Christiana, which rests on a stratuni 

 with orthoceratites ; but the organic remains being already very 

 rare in certain strata of phyllades, may it not be possible that 

 they are still more rare, or have disappeared altogether, in those 

 which are ranged with primitive substances ? 



Certain families of mollusca, such as oysters and gryphites^ 

 in passing to the fossil state, have preserved their shelly covering 

 in all localities and all strata. Others, such as those of the 

 volutse, cypraeae, crassatellse, and others, have disappeared in 

 almost all the places where crystallization or petrifaction has 

 taken place. The terebratulites are preserved almost every 

 where ; still, in certain ancient strata, such as those of Vologne 

 Coblentz, Tenior, in the Alleghany Mountains, and in Virginia, 

 they have disappeared, leaving only their internal and external 

 moulds. 



The polyparies, the serpulse, and, in general, all such shells 

 as adhere to certain bodies, are better preserved than the others. 



The solid parts of the stellerideae, echinodae, and encrini, in 

 passing to the fossil state, are changed into calcareous spath, 

 which breaks into rhomboidal laminae ; and it is always easy to 

 ascertain if these bodies are fossil, by the spathic state in which 

 they are found. The testa of these animals is very often pre- 



