MODE III. CLAV ROCK. 271 



spotted or striped. Mr. Jameson, in his Mi- 

 neralogy, has promised a more particular ac- 

 count of thonstein ; which he has not however 

 accomplished in his Geognosy, where he only 

 informs us that the Pentland hills, near Edin- 

 burgh, present examples. Dr. Babington, in 

 his catalogue, mentions clay porphyry from the 

 vicinity of Edinburgh ; but gives no examples 

 of the clay rock, which seems however to form 

 a great part of that vast chain of mountains the 

 Andes. In Chili entire mountains are com- 

 posed of brown or black clay rock. 



This substance frequently occurs in coal and 

 other mines, where it receives avast variety of 

 provincial names, according to the fancy of the 

 miners. In coal-mines it is commonly a shale, 

 and alternates with beds of sand-stone, which 

 also in such circumstances receives fanciful de- 

 nominations*. 



Clay rock, from Saxony. 



The same, from the Andes.. 



The same, from Pentland hills. 



* What is called the clay-bed of the Leadhills, in Scotland, 

 varies from the softness of tough clay, to the hardness of striking 

 fire with steel ; in the language of miners, from mell and wedge to 

 Hasting : and this too at a depth from forty to fifty fathoms. 



Near Lesmahago, Lanarkshire, is a lead-mine in clay slate : the 

 metal being in a vein of sulphate of barytes, five feet wide. G. L- 



