476 FOSSIL INVERTEBRATED ANIMALS. 



principle which is developed in all organized bodies. It is well 

 known that the most celebrated chemists have regarded earthy 

 substances as oxides ; and every thing leads us to believe that 

 this conjecture is highly probable. 



Small rock crystals, with two points, were found by Demeste 

 between the fibres of the heart of a petrified tree j which fibres 

 were ligneous and combustible^ while those of the circumference 

 were entirely petrified. According to Patrin, it would appear 

 that these were owing to the elementary principles of the wood, 

 which were disengaged, under a gaseous form, by the eflPect of 

 putrefaction, and which, finding themselves free in these inter- 

 stices, had formed there crystals by the effect of the same 

 chemical combinations which had converted into silex the lig- 

 neous parts which were not altered. 



It is probable that, among these principles of the wood, and 

 of all organized bodies in general, we should reckon as essential 

 a phosphoric principle — as their phosphorescence, at the time 

 of decomposition, more than seems to prove. Now, it appears 

 certain that phosphorus is equally a constituent principle of 

 quartz, according to the observations of Dolomieu. 



It is easy to perceive that, of the two hypotheses we have now 

 explained, that of Patrin is by no means the most simple. He 

 also employs it to refute the explanation, given by M. Haiiy, of 

 the formation of a nucleus of pure silex, which often takes 

 place in the interior of shells and of fossil echini, according to 

 this philosopher, by the intromission of a liquid, charged with 

 stony molecules, into the cavity of these shells, and ursini. 

 With Patrin, the theory of the gases suffices for all this, and is 

 contradicted by no fact in nature. He says, that we may well 

 suppose that a gaseous fluid penetrates the entire mass of a 

 substance so porous as chalk ; and as this fluid cannot produce 

 the matter of silex but by its combination with the fluids con- 

 tained in organized bodies, it converts into silex only the sub- 

 stance itself of the molluscous animal contained in the shell. 

 When the interior part of this body, which is the most exposed 



