99 



TAB. CCCLIV. 



It is not always that the substance which contains the 

 same ingredients as Slate, has the schistose fracture, as ap- 

 pears by its being turned in a lathe on some occasions. It 

 is rather remarkable that the Snake-Stone from Ayrshire is 

 a variety of the same substance as Slate, but is not generally 

 recognized to be such, on account of its possessing the slaty 

 fracture when in large pieces only, not showing it when 

 broken small. It is imported as a valuable and truly useful 

 article in many branches of manufacture; as for smooth- 

 ing copper, marble, 8cc. For the latter it is formed into 

 the shape of mouldings, as in the upper Jigure. This sub- 

 stance is known in a great measure by its being so regularly 

 spotted, which, perhaps, has obtained it the appellation 

 of Snake-Stone, by which it is well known among work- 

 men. The light brown colour is analogous to the unspotted 

 part of a snake's skin. I have gathered nearly the same in 

 Cornwall, and some varieties are to be found, with the dark 

 spots beautifully relieved by satiny Talc of a looser tex- 

 ture : — see the under Jigure. I have specimens nearly like 

 it, but more indurated, from Keswick. The black spots 

 seem to be Hornblend, Chlorite, or Manganese. 



In the upper specimen the black is generally of an equal 

 hardness and texture with the rest, or it would not suit the 

 workmen. When a stone from any quarry is found to have 

 the proper qualities, it becomes of much consequence, and 

 is a valuable article of commerce. 



i 2 



