142 . III. DIST. CHAR. Substance. 



SILICEOUS ORDER. 

 * Homogeneous Stones. 

 Quartz. 

 Massive. Kirw. p. 242. F. An. and Veg. v. 



Berg. Med. Syst. Foss. p. 78. 

 Crystallized. sometimes lines the cavities of 

 petrified shells,, &c. &c. but cannot be said 

 properly to form their substance. 

 Arenaceous. F. An. and Veg. Arenaceous 

 quartz exists in sandstones f, and in this state 

 frequently constitutes the matter of petrifac- 

 tion. 



Hornstone. 

 Splintery. Chert. Kirw. p. 308. F.An.ff 



f- Masses of granular and arenaceous quartz are found in the 

 veins and cavities of our Derbyshire limestones, particularly near 

 beds of chert, and in this state form the nuclei to petrified shells 

 and other marine relics. 



ft Bergman considers petrifactions of chert as rare This 

 stone is frequently attendant on primary rocks, in which case it is 

 of course destitute of organic remains; but when it occurs in 

 mountains of a secondary formation, as in Derbyshire, it usually 

 abounds in petrifactions. Some mineralogists, as Dolomieu, and^ 

 lately, Babbington, have asserted that Chert, Petrosilex, or 

 Hornstein of the Germans, is found only in primitive mountains. 

 Dolomieu, however, makes a distinction between splintery quartz* 

 as he calls this stone when it is found in secondary limestone, and the 

 petrosilex of primitive rocks. Dr. Babbingion does not, appa- 

 rently attend to this distinction ; his assertion, therefore, that petro- 

 silex or chert is found only in primitive mountains, must be found* 

 cd on a mistake. 



