Siliceous Genus. 107 



in powder. The finenefs of fome fpecies of 

 fand is fo great as to pafs through fie ves, that 

 contain 10,000 vacuities in the fpace of an 

 inch, as Mr. Wedgeivood one of the moft 

 celebrated manufacturers of earthen ware 

 in Europe, has aflured me. Hence this 

 Earth has been found fufpended in fome 

 waters in the quantity of i grain in a gallon. 

 See 2 Bergm. 47, and Cadet in the Memoirs 

 of the French Academy for 1 767. 



SPECIES II. 



Siliceous Earth intimately mixed and partly 

 combined 'with about \ of its 'weight of Ar- 

 gill, and ^ of its 'weight of Calcareous 

 Earth. 



Common Flint or Pebble, Hornflein^ Kiefel of 

 the Germans. 



This ftone is found of all colours, or va- 

 riegated with veins of different colours ; it 

 is commonly covered with an opake white 

 cruft, which feems of the fame nature, but 

 more imperfectly combined ; this cruft ad- 

 heres to the tongue like clay, yet ftrikes fire 

 with fteel, fo that probably it contains a lar- 

 ger proportion of argill than the kernel. 

 Flint is always femi-tranfparent in thin pie* 

 ces ; its hardnefs is various, though it always 

 gives fire with fteel ; its texture is folid, 



whereas, 



