South-western Coal District of England. 231 



The sandstone is separated from the limestone by intervening beds of shale, 

 which, having readily yielded to denuding forces, is usually excavated into a 

 line of valley. The denudation of the shale is so deep and sudden at the foot 

 of Blackdown, that high precipices are formed by the truncated edges of the 

 incumbent beds of limestone in the scar of Shute-shelf Hill on the south, and of 

 Burringdon ham on the north. The blue varieties of the lower limestone-shale, 

 along the southern base of Blackdown, so nearly resemble in external appear- 

 ance the shale of the coal-measures, as to have occasioned several fruitless and 

 expensive trials for coal. Shafts have been sunk with this view in the lime- 

 stone-shale, under the scar of Shute-shelf, and further eastwards near to Char- 

 terhouse farm. Had these shafts been deep enough, they would have pene- 

 trated to the old red sa/idstone. 



This elliptical tract of old red sandstone and limestone-shale, exceeding 

 8 miles in length, is completely encircled by a zone of mountain limestone, 

 except at a lateral opening near Loxton, about f of a mile broad, through 

 wiiich the streams, collected in the western half of the inclosure, find their 

 way into the Axe. 



This calcareous zone, though of inferior height to the sandstone summits of 

 Blackdown, is yet of considerable elevation. In the scars both of Shute-shelf 

 and Burringdon ham the limestone strata are highly inclined, in the former to 

 the south, in the latter to the north ; and they would, if continued, form an arch 

 over Blackdown. In the northern band of limestone, at the entrance of the 

 Rowborough defile, in Doleberry camp, we have a curious instance of fan- 

 shaped stratification, a section of which is represented in PL XXXII. fig. 3. A. 



Both the northern and the southern limestone-ridge is broken through by 

 transverse valleys, which, when near together and precipitous, intercept de- 

 tached summits, affording, from their steepness and insulation, positions of 

 great military strength. Thus, on the northern side of the chain we have the 

 fortified positions of Banwell and of Doleberry, the latter bounded on the west 

 by the defile leading from Churchill to Rowborough, and on the east by the 

 ravine of Burringdon Combe : on the southern side of the chain we have the 

 conical summit of Crook's Peak, which yielding but little in height to Black- 

 down, and much exceeding it in the mountainous character of its outline, forms 

 one of the most striking features in the western portion of the Mendips. From 

 Cross to Cheddar the southern declivity of the chain towards the valley of the 

 Axe is unusually abrupt, and the transverse valleys which penetrate into it, are 

 distinguished by a wild and rocky character. We have here two striking ra- 

 vines; viz. thatof Tining's gate, and the yet more stupendous chasm of Ched- 



VOL. VI. 2 H 



