PREFACE. ix 



<3ered ftones, their confideration is of no life, 

 ftriking fire with fteel, has often been given 

 as a teftof pufe filiceous earths, but it is now 

 known, that well baked clay, to fay nothing 

 of other compound fubftances, will exhibit 

 the fame appearance. 



Texture^ all its varieties as granular, la- 

 mellar, fibrous, fcaly, equable, &c. are com- 

 mon to fubftances, widely different ; thus the 

 fibrous is found in fome varieties of gypfum, 

 in afbeftos, fhoerl, pumice, pyrites, antimony, 

 haematites, malachite, cobalt, and arfenicai 

 ores, the fcaly in lead and iron ores, mica, 

 limeftones, gypfum, the lamellar, granular, 

 and equable, are ftill ofWider extent. 



Shape, the varieties of this even when re- 

 gular and determinate, are endlefs, as may be 

 feen in Mr. De Lijle's Treatife, and muft be 

 fo, as they depend of various external acci- 

 dents, thus he finds 32 varieties in the fhape 

 of calcareous fpar, 14 in that of gypfum, 9 in 

 that of fluor, 1 6 in that of quartz, befides its 

 monftrous forms, equally regular as the reft, 

 19 in that of felt fpar, &c. and not only the 

 fame fpecific fubftance is fufceptible of various 

 fhapes, but various fubftances fpecifically dif- 

 ferent, affume the fame fhape. Thus the 

 native calx of arfenic, blende, cinnabar, and 

 grey copper ore> often appear in a tetrahaedral 



form ; 



