83 Prof. Sedgwick on the Carboniferous Chain 



14. Alternations of hard, thin-bedded, brown gritstone, and dark-coloured 

 carbonaceous shale, with two or three beds of coal. Average thickness along 

 the principal line of section about 60 feet. 



In some of the neighbouring regions (for example among the mountains of 

 Swaledale Head), this group contains two or three thin beds of crow-lime- 

 stone, and its aggregate thickness is about 200 feet. 



The only bed of coal which has been much worked, is in the lower part of 

 the group, and varies from eighteen inches to nearly four feet in thickness. 

 At Tan Hill near the highest part of the road from Brough to Arkendale, and 

 at Turna Fell near Hawes, this coal is of good quality, and is extensively 

 worked. Near the top of Penigent, of Whernside, and of Great Colm, 

 horizontal drifts have been carried into this bed ; but it is of bad quality, and 

 not fit for domestic use, being mixed with ferruginous and pyritous shale*. 

 The hard, brown beds of grit alternating with the carbonaceous shale, are 

 provincially termed sill-stones. 



15. Second Millstone Grit. The limits of this group are very ill defined, 

 and its thickness varies from 40 or 50 to 120 feet. 



At the top of Penigent and Whernside it is represented by an open-grained, 

 thin-bedded, siliceous grit, no part of which has the appearance of millstone. 

 But at the top of Baw Pell, Wildboar Fell, and some of the Swaledale hills, it 

 passes into great, thick beds of the finest millstone grit. 



16. Alternations of gritstone and shale, with traces of a thin bed of coal. 

 Thickness about 100 feet. 



The band of coal is found, here and there, near the bottom of this division. 

 In general the subordinate shales are meagre, sandy, and micaceous ; and 

 the alternating beds of grit are thin and open-grained, like certain bands 

 associated with the groups of millstone grit. 



There is just a trace of this group at the top of Wildboar Fell, and perhaps 

 at the highest point of Whernside, under the soil and morass. It is best ex- 

 posed under the highest summit of Shunner Fell, and near the top of a part 

 of the high ridge between Mollerstang and Swaledale Head. 



17. Upper Millstone Grit. Thickness 120 feet. 



* As not less than three beds of coal are found, here and there, subordinate to this group, it 

 would be impossible to prove that in all the above-mentioned places the coal is precisely upon the 

 same parallel. It is, however, so considered by the miners of the neighbouring districts. Near 

 Kirkby Stephen it generally passes under the name of the Tan Hill seam, that being the locality 

 of the most valuable coal work, established upon the bed in question. There, however, the re- 

 lations of the coal to the neighbouring groups are somewhat obscure ; and in a general description 

 the Turna Fell seam is perhaps the best name which can be given to it. 



