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A. 



47 



'The Tricherium refembles the Amiantus botl 



1 



of its fibres, or general 

 acid. 



but it yields eafily to the fire 



the difpofition and appearance 





gh 





/ 



I. 



Clangofus e nigro carulcfc 



5 



O 



SCHISTUS 



The Jlate, 

 and dead ft 



hone 



2. Ater,fcript 



3. Friabilis nigricans. 



4. Cinereus folidiuf cuius fcriptura can a. 



5. Friabilis fragment 1 s angulatis fubquad, 



6. ftubcinereus, & Jubcceridcus^ van us. 



The Hone. 



The Schijlus is a ftone of a lamellated ftrudture, fmooth grain, and opakc appear- 

 ance j it is generally found in flakes horizontally difpoied, but is fometimes divided 

 perpendicularly alio ; and is frequently connected by a foreign fiuor. ' 



T. 



VI. 



De argilld & argillaceis. 



Of Clay 



> 



and clayey Subftances. 



H E ftickey nature of the clay does fufficiently (hew it a peculiar kind, and 

 intirely diftincl: from both the foregoing and the following : it is naturally ftiff 

 andfvifcid, nor does it diffolve in water but with difficulty : it hardens in the fire, 

 and when pufhed with a ftrong heat, turns into a ftony or vitrefcent mafs. The pro- 

 ductions of this clafs, when concreted into a folid form, give fire freely with fteel, and 



generally bear a fine polifh 5 but are never injured either by the acid, or a moderate 



degree of heat. 



Its moil diftinguifhed kinds are the 



f I. Teffulata. 



ARGILLA 



Clay. 



I 



2. 



I 



Potters clay. 

 Subpinguis fijjilis. 

 The Refiners clay. 



3 . Arena mixta. 

 Brick clay. 



4 



re 



rra 



Clayey foil. 



& fabulo 



[mixta. 



r * 



ane 





This, like the foregoing, appears to have its various degrees of mixture as well as 



compofition ; and the moft fimple among them feem to be thofe that fhew themfelves 

 in a tranfparent folid form, which we likewife conclude to be the effect of a pe- 

 culiar tranfparent fluor of this nature : and that fuch a fubftance exifts every where 

 in our globe, is evident from the various appearance of cryftals and ftint, as well as 

 from the different ftrata in pebbles, &c. 



The vitrefcent quality of thofe productions, probably, proceeds from the plaftick 

 mature of the argilla; and the igniferous, from their native hardnefs. 



The principal productions of this clafs are, 



Conico cylindracea utrinque attenuata. 

 Needle cryftal. 



Columnar is utrinque py rami data. 

 Columnaris adfummum pyr ami data. 

 1 °. CRYSTALLUSj 4. Utrinque pyramidata columnd nulla predita. 



Cryfial 



Ad fummum pyramidata columnd nulla predita. 

 Sub -rotunda > fuperficie fcabro. 

 Pebble cryftal. 



Informis rupejlris aquea. 



Rock cryftal. 



The 







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