174 . III. DIST. CHAR. Soil. 



** In substance, 



The mineral seat is either earthy, saline, metal- 

 lic, or inflammable. 



The Earthy ( sedes terrea) consists of 



Limestone, generally in strata including its va- 

 rieties, as marbles, swinestones, &c. Common. 



Calc. Spar, in veins. Rare. 



Marlites, in strata. Common. 



Marls, in strata, very common in veins, rare. 



Chalk, in strata. Common. 



Gypsum, in strata, and masses. Rare. 



Clays, in strata. Common. 



Shales, in strata. Common. 



rounding strata, are never similar : they are, doubtless, sometimes 

 found to be the same. In such instances, which are by no means 

 common, it is probable, the extraneous fossils of the vein have ori_ 

 ginated from those primarily lodged in the substance of the strata, 

 but extruded during their desication, and the consequent formation 

 of the rift. It will easily be conceived, that those animal or 

 vegetal bodies, which were laid bare by the contraction and 

 splitting of the surrounding mineral matter, would frequently 

 remain adherent to, or sticking in, the surfaces of the fissure then 

 formed ; and such, indeed, is the state in which the extraneous 

 fossils of veins, when the same as those of the native rock, fre- 

 quently present themselves. During the increase of the rift, in 

 its width, by subsequent contraction of the strata, many of these 

 extraneous bodies would be entirely detached, however, from 

 their original matrix; and of course enveloped in the mineral 

 matter, gradually introduced into the vein. (v. p. 25. note. art. 

 23. 24. and p. 32. note ft-) 



