MODE II. CLAY SLATE. 267 



Aspect 2. With impressions. Shale, with the 

 impression of the skeleton of a fish in a lighter 

 colour, from Hessia. 



Shale, with the impression of an ammonite, 

 from Chamouni. 



The same, with impressions of various vege- 

 tables, chiefly gigantic ferns, from various coal- 

 mines. 



Variety. Bituminous shale, with various im- 

 pressions. 



There are two substances often found in clay 

 slate, and considered as of a kindred nature, but 

 they never appear in the form of rocks. 1. Black .Black chalk, 

 chalk, so called because it is used in drawing, 

 and which, according to Weigleb, contains 1 1 of 

 carbon. 2. Hone, which is as proper and so- Hone, 

 norous a name as novaculite, or whet-slate. Some 

 clay slates and sand-stones form the coarser whet- 

 stones, used by cutlers. The finest hones are 

 said to be- brought from Turkey, but they are also 

 said to be found in the neighbourhood of Namur, 

 in Flanders. Brochant says that it is also found 

 in Bohemia, in Saxony (Seifensdorf, near Frey- 

 berg), in Siberia, in Stiria: lastly, at Lauenstein, 

 in the Margraviate of Bareith, where it is wrought. 

 It often seems to form the passage to indurated 

 talc, and is sometimes covered with efflorescences 



