MODE XII. . SLATE. 



Aspect 2. Killas, from Cornwall, many va- 

 rieties ; blue, grey, or whitish yellow. If it con- 

 tain only 6 of iron, it belongs to the argillaceous 

 or to the magnesian schisti. 



STRUCTURE II. MASSIVE. 



The same identic substance of which slate is 

 composed has been discovered in France, and 

 other countries, in a massive form, or stratified 

 with the seams at great distances, and incapable 

 of being split into thin plates, like common slate. 

 It may probably be often discovered in the vicinity 

 of slate-quarries. 



The slate with impressions so frequently found 

 with coal, and called shale, is commonly of an 

 earthy texture, and belongs to clay-slate. 



Saussure mentions slate in columns like basalt*. 

 He also enumerates the following : 



598. Granite, joined with slate; the last being 

 composed of mica and pierre de corne. 



1862. A slate, with mica, in leaves thinner 

 than paper, sometimes straight, sometimes undu- 

 lated. It is, according to Saussure, a mixture of 

 ferruginous clay and mica. 



* i. p. 523, 4to. 



