S30 



ANALYSTS O? POLISHING SLATf.. 



Where found. 



Described. 



Stratum 

 described. 



XI. 



Observations on Werner's Silex Sthistosus Politorius, • 

 Polterschiefer, from Biffin, in Bohemia *. 



: A HIS substance, called polishing slate, is found about thrcQ 

 miles south of Billin, in Bohemia, immediately under the 

 vegetable mould, and less than a yard deep. It is of a yeU 

 lowish colour, and slaty texture ; has an earthy appearance. ; 

 and leaves a coloured mark on cloth. Between the fingers 

 it is easily reduced to a powder, which is a little rough to the 

 feel ; it adheres strongly to the tongue ; it is infufible. Its 

 specific gravity according to Mr. Habcrle is 0*6 ; and if left 

 twelve hours in water 100 parts absorb 117. In Saxony 

 it is known in the shops by the name of silver tripoli. 



In the place where I observed it, near the top of a 

 pretty high hill, it forms the superior part of a stratum, 

 which increases in density as you penetrate into it; and in. 

 some places at the depth of two yards it is compact, with 

 a yellowish and somewhat shining aspect, like that of cer- 

 tain semiopals : but it is not so hard, or so heavy. From 

 every thing I observed on the spot, the polishing slate is 

 nothing more than a portion of this stratum, the texture of 

 which is loosened and altered by decomposition. Accord- 

 ing to Mr. Reuss, who lives at Billin, the stratum includes 

 remains of vegetables, and impressions of fish. Everything 

 besides indicates, that it is a recent alluvial production. 



Mr. Bucholz has analysed both the polishing slate and 

 the adhesive slate, klebschiefer, that accompanies the meni- 

 lite of Menil-Montant, which had been considered as a va- 

 riety of it : and as Mr. Klaproth has made a more full and 

 complete analysis of the Klebschiefer than that he first gave 

 the public, we shall here present the three analyses in a com- 

 parative view. 



99 99 



* Journal des Mines, K. 121, p. 77. 



98-25 



