YOREDALE ROCKS. 167 



In Derbyshire, Mam Tor, or the ' Shivering IMountain,' is com- 

 posed of rocks belonging to the Yoredale Series, which is there 

 sometimes called the Limestone Shale. The series forms a wet 

 soil, causing landslips of great extent, beneath the Millstone Grit 

 summits ; and the scarp of Mam Tor has been caused by a gigantic 

 landslip which has carried away one side of the hill. In this dis- 

 trict the Yoredale Rocks comprise the following divisions : — 



Yoredale Sandstones, about 2000 feet. 

 Shales, with thin earthy limestones. 



Fine sections of the Yoredale rocks may be seen by walking from 

 Back Tor to Edale (Grindsbrook), a magnificent gorge in the grits 

 on the flank of Kinder Scout. ^ 



In Leicestershire and Monmouthshire the upper beds of the 

 Carboniferous Limestone consist of limestones alternating with 

 dark shales. 



In Glamorganshire, immediately above the Carboniferous Lime- 

 stone of Gower, at Penrice, and between Llanrhidian and Oyster- 

 mouth, there is a considerable development (1600 feet) of black 

 shales with sandstones, to which the name Gower Series has been 

 applied. These beds appear to represent the Upper Limestone 

 Shales, and perhaps also the Millstone Grit. At Tenby they are 

 but a few feet thick, but there they contain beds of dark limestone, 

 and yield Goniatites, reminding one of the Black Limestones of 

 North Devon that occur at the base of the Culm-measures. (See 

 sequel and Fig. 29.) 



In the Forest of Dean the Upper Limestone Shales are estimated 

 by Mr. E. Wethered to have a thickness of 1 16 feet. 



At Clifton, between the Carboniferous Limestone and Millstone 

 Grit, there is an alternation of red and grey limestones, shales, and 

 sandstones, 300 or 400 feet in thickness, sometimes classed as the 

 Upper Limestone Shales. These beds are shown in the Avon cliffs 

 on either side of the Observatory Hill. To the north of this hill 

 the beds are faulted against the Carboniferous Limestone — the 

 downthrow being estimated at about 11 50 feet.^ No less than 52 

 species of fossils, principally Corals, Crinoids, and Brachiopods, have 

 been recorded from these beds. At Vobster, near Mells, to the 

 north of the Mendip Hills, black shales intervene between the 

 Carboniferous Limestone and Millstone Grit. (See p. 161.) 



Economic products, etc. 



The lead-mines of Alston Moor, Weardale, Arkendale, Wensleydale, and 

 Swaledale are situated in the Yoredale rocks. 



Rotten-stone, due to the removal of the calcareous portion from siliceous lime- 

 stone, is met with near Ashford and Bakewell in Derbyshire, and elsewhere. 



The fine-grained micaceous grit-stones of the lower series are much used for 



^ P. Geol. Assoc, v. 189. 



2 C. Lloyd Morgan, Q. J. xli. 146. See also \V. W. Stoddart, Proc. Bristol 

 Nat. Soc. (2), i, 330. 



