148 MINERALOGY OF ST ANDREW'S, 



very liable to decomposition. I observed that 

 those sandstones which contained much minera- 

 lized vegetable matter, were the most easily de- 

 composed, and were frequently So friable, that 

 they could be crumbled down between the fingers. 

 The sandstone occasionally contains a little mica, 

 and likewise mineral charcoal, and not unfrequent- 

 ly small globular pieces of iron-pyrites. 



11. Coal 



A few beds of coal occur in the beds of sand- 

 stone. These are, however, of trifling importance, 

 very seldom more than a few inches, and never 

 exceeding a foot in thickness. They are principally 

 slate-coal, containing numerous petrifactions of 

 reeds, flattened and compressed. Thin layers of 

 pitch-coal also occur, both in the slate-coal, and 

 also in the sandstone. In one of the largest beds 

 of coal, I observed globular concretions of sand- 

 stone, having the thin layers of coal surrounding 

 them on all sides. 



III. Slatt-Clay. 



This rock occurs in beds of various thickness, 

 and of every degree of hardness and density. It 



