. III. DIST. CHAR. Mode. 53 



ture, and in such as possess an open and granular 

 structure.f 



Mineral matter, dissolved in water percolating 

 through strata of stone, &c., may be separated from 

 its menstruum, either by crystallization, or simple 

 precipitation ; and hence, petrifactions bj redinte- 

 gration have a sparry or an earthy structure, ac- 

 cording to the mode, in which the constituent sub- 

 stance has been deposited crystallization produc- 

 ing sparry or crystalline stones (foliated of Werner's 

 school ) precipitation, those which possess the earthy 

 fracture. Both processes, however, are frequently 

 apparent in the same specimen, especially among 



t Through means of which, the escape of the organic, and the 

 subsequent infiltration of mineral particles, have been effected. 

 The stones, however, in wlrich petrifactions are lodged, are not al- 

 ways now open or porous: they frequently possess a comparatively 

 close or compact texture. This is readily accounted for, when 

 we consider, that the process, which fills the mould of the petri- 

 faction, is also that, by which a superior degree of solidity may be 



induced in the surrounding matrix. Mr. Kirwan observes, that 



the induration produced in stones, by infiltration, is more consider- 

 able than that, which is the effect of desiccation, as the minutest 

 particles of bodies are conveyed by it into the smallest interstices. 

 He adds, that such infiltration is not an imaginary processes appears 

 by an elegant observation of Mr. Werner's, viz., that where various 

 strata of a different nature occur, the petrifactions that are found 

 in the inferior, are frequently filled with the matter of the supe- 

 rior, instead of that of the stratum which contains them. v. Geoiog. 

 Essays p. 45. Also p. 128, where the induration of stones of a 

 loose texture, by infiltration, is treated of more at large. 



