70 Prof. Sedgwick on the Carboniferous Chain 



in several other places, at the junction of the carboniferous chain with the 

 unconformable greywacke mountains of Westmoreland. There can, there- 

 fore, be no doubt that the lowest beds of the carboniferous system of this 

 region rest upon an irregular surface of unconformable grey wacke slate, from 

 which they are separated, here and there, by great irregular masses of old 

 red conglomerate. 



The whole overlying series is essentially composed of alternating masses of 

 limestone, sandstone, and carbonaceous shale, terminating in a great system 

 of beds connected with the millstone grit. The limestone groups are incom- 

 parably the most continuous and the best defined, and form a kind of frame- 

 work by which all the other component parts are held together. They are 

 six in number, and will be referred to in the several sections, under the fol- 

 lowing names : — 1st, Great scar limestone. 2nd, Black marble limestone. 

 3rd, Strong post limestone. 4th, JVold or Mosdale Moor limestone. 5th, Four- 

 fathom limestone. 6th, Main, or twelve-fathom limestone. The names given 

 to the 1st, 5th, and 6th groups are in common use in the North of England, 

 and on that account ought not to be changed. The other three groups might 

 be conveniently designated in the section by the names 2nd, 3rd, and 4th 

 limestones : but these names would cease to have any propriety if applied to 

 remote parts of the same chain, and therefore ought not to be made use of, 

 except in local description. 



To prevent a frequent repetition of nearly similar details, I shall commence 

 with an enumeration and description, in the ascending order, of all the re- 

 markable groups of strata which appear upon different parts of the lines of 

 section. 



§ 2. General Section of the whole System, in the ascending order*. 



1. Great Scar Limestone. Total thickness about 600 f feet. — The term 

 scarj in the dialects of the North, means any bare precipice on the face of a 

 mountain, and is applied with great propriety to this limestone, which in all 

 parts of its range is marked by grey precipices and mural escarpments. The 

 grey scars near the base of Ingleborough, of Penigent, and of Whernside; 

 the mural precipices above Giggleswick and Malham, and the magnificent 

 cavernous gorge of Gordale, are among the striking exhibitions of this de- 

 posit, and present a nearly exact counterpart to the features of the same lime- 

 stone in the High Peak of Derbyshire. 



* SeePl. VI. fig. 1. 



t This number is merely approximate, and there are only a few places where the whole thick- 

 ness is visible. It is probably very variable, as the deposit has taken place upon an uneven, un- 

 conformable surface. 



