from Penigent to Kirkhy Stephen, IIS 



(b.) Alternations of sandy, micaceous shale, and brown, micaceous sandstone, 

 generally of a coarse, flaggy, or slaty structure. 



(c.) Strong beds of hard, micaceous gritstone, alternating with similar 

 masses of slaty texture, and generally surmounted by a few beds of meagre, 

 sandy shale. 



Wherever the shale beds abound, the thickness of the whole group is ex- 

 tremely variable. The micaceous flagstones of the middle portion are some- 

 times wanting, and the group is then composed of carbonaceous shale, iron- 

 stone, and gritstone. One of the finest exhibitions of this group is at the 

 waterfall of Hardraw Scar near Hawes. It is also well exposed by the many 

 torrents which descend from the mountains on both sides of the vafley of Dent. 



3. Second Limestone, or Black Marble Group. Greatest thickness about 

 45 feet; average thickness about 30 feet. 



This group is distinguished from all the rest by the regularity of its strati- 

 fication, which often makes it look, on the face of a precipice, like a rude 

 work of masonry ; also by its dark-coloured, compact beds with a conchoidal 

 fracture*. Some of these beds take a beautiful polish; and when they can 

 be raised in large slabs free from white spots, and without seams or cross 

 joints, are of considerable value. Unfortunately many of the quarries are 

 almost spoilt by the cracks and fissures which traverse all the component 

 strata : and many of the more solid masses are injured by the imbedded or- 

 ganic remains (such as Encrinites, Caryophylliae, Productas, Spirifers, &c. 

 &c.), replaced by pure white carbonate of lime containing little of the carbon 

 and bitumen which form the dark colouring matter of the rock. 



The thin bands of bituminous shale, separating these limestone beds, also 

 contain organic remains ; and, among the rest, innumerable specimens of the 

 Producta latissima and P. Scotica, which may be almost considered as charac- 

 teristic of this group. 



Nearly all the quarries, in the neighbourhood of the lines of section, from 

 which the black marble has been exported, are found in the valley of Dent. 

 I have however traced them, in the exact position here indicated, through 

 Horton parish, on both sides of Chapel le Dale, in Kingsdale, and in Gars- 

 dale. They may be also traced through a part of Wensleydale, and appear 

 at the top of the precipice of Hardraw, over which tumble the waters of a 

 mountain torrent, forming one of the grandest waterfalls in the North of 

 England. They are there however so much changed in structure, that they 



* Most of the beds before polishing have a bluish tinge, and their weathered surfaces are of a 

 greyish colour. On being burnt, they are reduced to a beautiful white calx, all the colouring bi- 

 tuminous matter being driven off. 



VOL. IV. — SECOND SERIES. L 



