Siliceous Genus. 1 1 * 



fait affecT: it like the former fpecies. Mr. 

 Gerhard fays that fome forts of jafper melt 

 per ft : thefe contain an over proportion of 

 iron, or elfe calcareous Earth, and then form 

 the link betwixt cherts and jafpers. 



The green jafpers contain iron in a femi- 

 phlogifticated ftate, and have often been con-^ 

 founded with malachites, but thefe latter 

 never give fire with fteel, to fay nothing of 

 the entire difference of their compofition. 

 Red jafpers contain iron more dephlogiftica- 

 ted. 



Sinople is a dark red jafper or flint, 1 which 

 ftrikes fire with fteel, and affords in the dry 

 way 10 per cent, of iron, and melts into a 

 black flag. Rmm. Hifl. Ferri, 189. If 

 tried with the Pruffian alkali, it would pro- 

 bably mew 1 8 or 20 parts of iron, as this 

 al way sfeparates nearly double the quantity of 

 iron that can be e^trate4 in the dry way. 



Of the fpontaneous Decompofition of Stones by 

 long Expofure to the Air. 



Flints, jafpers, petro-filex, felt-fpar, gra- 

 nites, lavas and ferruginous ftones, have fre- 

 quently been faid to be decompofed by long 

 expofure to the air, and the obfervations of 

 Mr. Greville and Sir William Hamilton have 

 removed every (Joubt I entertained on this head. 



With 



