56 . III. DIST. CHAR. Mode. 



of the organic,, is followed by a deposition of mine- 

 ral particles, which entering, by filtration,, the tex- 



harder and more durable alone giving their figure to the substituted 

 matter. For these, as the wood in plants, the bones in animals, 

 &c., preserve their general form, after their vascular structure has 

 become, by partial decay, pervious to the infiltrating fluid; in- 

 deed, until the fibrous and less perishable portions of their fabric are 

 a Is destroyed ; and then the mineral, deposited in the first stages of 

 the process, acts as the mould to the subsequent impregnations. 

 Again, although the original should preserve its form to the last, 

 yet if it part with organic matter, faster than the surrounding 

 waters can supply the deficiency with petrescent particles, either 

 no petrifaction will be produced, or one that retains but slight ves- 

 tiges of an organic structure. On the other hand, if the water 

 deposite mineral matter in great abundance, and the immersed 

 body decay slowly, an incrustation, and not a petrifaction, will be 

 the result. 



The theory now proposed to account for the changes induced 

 in organized bodies, by the process we have termed intromission, 

 is nearly that, which has been adopted by Bergman, Kirwan, Walch, 

 Daubenton, and most modern authors, who have written directly 

 or indirectly on the subject of petrifactions. Another hypothesis, 

 however, has lately appeared from the pen of the ingenious Mr. 



Parkinson, which may be thus briefly stated. Disclaiming the 



idea of a mineral deposition gradually assuming the form and 

 disposition of the organic particles, while their removal by putre~ 

 faction, &c., is taking place, this gentleman conceives, that, in ge- 

 neral, no insinuation of stony matter will be effected, unless the 

 original body be prepared to receive it, by the agency of bitumi- 

 nization. In this state, wood (the <. ily substance to which Mr. 

 Parkinson's theory has, as yet, been applied) is frequently found 

 with little or no alteration in its texture, and yet so thoroughly 

 pervaded with water, " that it may be discharged from it as from 



