184 MINERALOGY OF THE PENTLAND HILLS. 



ving a greenish-black colour, appear allied to Com- 

 pact Slaty- felspar, because, like it, they decay with 

 a white crust, are thick slaty, and harder than the 

 grey-coloured varieties. It sometimes appears 

 more or less curved and waved in its structure, — an 

 appearance not unfrequent in transition clay- slate, 

 and which, like the curved and waved laminae of 

 more regularly crystallized bodies, is to be viewed 

 as the effect of crystallization. 



Hare Hill, as far as I could ascertain, appears 

 to contain much of this rock. It appears also on 

 the north-east and south-west corners of Black 

 Hill, and is frequent in the valley of the North 

 Esk river. 



11. Gjxy-Wacke, 



The grey-wacke which occurs in our district 

 is very small granular, and has but little of the 

 mechanical aspect of the common varieties of this 

 rock. It is composed of felspar, quartz, and some- 

 times a little mica ; and these minerals are so con- 

 nected together, as to shew that this rock is a che- 

 mical not a mechanical deposite. It occurs in 

 beds varying from a few inches to two or three 

 feet in thickness, and these alternate with the clay- 

 slate already described. I observed it near 

 Habbie's How, and also in the valley of the North 

 Ebk river. 



