41 



TAB. CCCXXV. 



Cotham Marble. 



Syn. Argillo-Calcite. Kirw. 



Cotham, near Bristol, affords this remarkably figured 

 Marie, which, according to the Bristol Guide, you may 

 often imagine is a fine drawing. It is a curious formation 

 of Marie and Clay, chiefly stained by Iron, and perhaps 

 occasionally by Manganese, forming, by settling in 

 moisture under peculiar circumstances, the top undula- 

 tions, sometimes representing clouds in a sky, while the 

 bottom imitates earth and water as in landscapes. The 

 fanciful figure to themselves in this something like a boat 

 and men in one part, and hedge-rows in another, with trees 

 in full foliage. The appearance of the different parts seems 

 in a great measure to point out the different substances. 

 The whiter part is softer, and has most Lime ; the bluer or 

 grayer have a dilute mixture of the black Oxide of Iron ; the 

 browner part being still harder in consequence of the state 

 of the Oxide of Iron, and the quantity of Clay or Alumine ; 

 for it must be remembered that Clay often has much Silex 

 mixed with it. The deposition indicates the mass to have 

 been more fluid in some parts than in others ; and perhaps 

 some conjecture might be formed as to the trees having 

 distilled in drops from the upper waved surface; but at 

 present we must rest with the theory, the practice of which 

 may lead to useful and certain truths. This substance is 

 found in broad slabs, and is cut transversely from the 

 thickness of an inch to a foot or more. It is sometimes 

 admired, for ornamental chimney pieces, and the masons in 

 the neighbourhood have used a geat deal of it for such pur- 

 poses. 



