MINERALOG Y, 4; 



to this order, than to; a great jnany o$h$g 

 earths J. .3 



SECT. XLI. 



The mineral bodies that are comprehended in 

 this order, are, indeed, fomewhat different from 

 one another. This difference, however, on firft 

 fight may be difcerned ; but, in regard to their 

 effe&s in the fire, and other chemical experi- 

 ments, it cannot be efteemed of any great con* 

 fequence, at .leail while we are no. farther ad- 

 vanced in the art of decompounding thefq. hard 

 bodies, and as long as no one has thought it 

 worth the trouble and expence to ufe thofe 

 means, which are already difcovered for this pur- 

 poie •, I mean the burning-glafs or concave mir- 

 ror ; and to continue fuch experiments which Mr, 



X It is not yet known, if there is any loofe earth of this 

 kind to be found, or if the indurated one is produced of a 

 clay, either pure, or mixed with the calcaieous earth, which 

 afterwards has been diflblved, in order to produce this : be- 

 caufe I have not yet, at leaft for my own part, found any 

 loofe earth that I can fufpeft to be a filiceous one, except 

 that which remains after (tones of this kind are decayed, and 

 which is found in form of a white crufl: on the fuiface of 

 thofe Hones that lye to the day, or on the earth. This being 

 afterwards worn off, and carried away by the water, is, per* 

 haps, gathered together in form of Jtrata. In the fame man- 

 ner window glafs likewife moulders in length of time: but 

 i: cannot, therefore, be fuppofeJ, that any fuch decayed par- 

 tides may, without being previoufly diifolved in fome new 

 mecftrnum, be reduced into their former fubftance. I. am 

 rather inclined to believe, that Tripoli is fuch a mouldered 

 filiceous earth, and ihat ihe method of Nature in producing 

 moil of the fl nty kind, is fuch as we do not rightly know, 

 nor have patience to follow, yet imagine that we in fome 

 mtafure imitate it in making of glafs, fince both thefe have 

 fume effect common wicu one another. 



