MODE II. CLAY SLATE. 



In chemical analysis it has sometimes hap- 

 pened that the chemist has ably performed his 

 task, but has mistaken the name of the sub- 

 stance. In like manner it was here necessary 

 to identify the rock, before proceeding to its 

 description. It has before been observed that it 

 may be divided into two kinds, which at the 

 same time vary considerably in their structure, 

 namely, primitive and secondary. 



STRUCTURE I. PRIMITIVE CLAY SLATE. 



Texture, schistose, sometimes in thin layers, Characters. 

 but more generally they arc thick and coarse; 

 fine-grained, sometimes almost impalpable. 



Hardness, marmoric, sometimes gypsic. Frac- 

 ture, slaty, sometimes approaching to earthy. 

 Fragments, amorphous, tabular, with sharp angles. 



Weight, carbonose to granitose. 



Lustre, sometimes dull, often silky. Opake. 



The colour is most usually grey, of various 

 tints ; but it may also be found of a straw yellow, 

 and various hues of red. It sometimes presents 

 streaks of a bluish white, or is mottled with va- 

 rious illinitions. 



Yellow clay slate, from Potosi. 

 Grey, from the Andes, Saxony, Scotland, and 

 other metallic countries. 



