230 Messrs. Buckland's and Conybeare's Observations on the 



higher part of the Tar Hall valley, and there spreading itself over the table- 

 land of the Mendips, entirely conceals the junction of the sandstone and 

 limestone within the bay formed by the sandstone ridge of North Hill. The 

 limestone, however, becomes exposed from Wigmore farm to the miserable 

 inn, miscalled the Castle of Comfort; but immediately to the north of the lat- 

 ter is again concealed by an elevated platform, consisting of longitudinal 

 strata of the abovementioned peculiar shelly chert, reposing on strata of ochre- 

 ous sand. [PI. XXXH. fig. 2. A. 3 This platform, which rivals in height the 

 ridge of old red sandstone, is about 2 miles long and 1 broad, and extends 

 northwards in the direction of East Harptree to the edge of the mountain 

 chain, where it terminates in a promontory projecting below two valleys, the 

 western called Lamb-bottom*, the eastern ascending towards Green-down. 



In this central part of the Mendip chain, the general bearing of its axis 

 being from south-east to north-west, the limestone flanking it is divided into 

 two parallel bands, having the same direction. The average breadth of the 

 north-eastern band is rather less than from 1^ to 2 miles. That of the south- 

 western is somewhat greater. This latter calcareous band extends to the brow 

 of the hills that overhang the valley of the Axe, and is uniformly covered 

 along its hangings by the dolomitic conglomerate. 



We now come to the western nucleus of old red sandstone. This nucleus, 

 towards its western extremity, occupies a low position, and in the valley that 

 extends from Roborough and Shipham to Winscombe and Loxton, is almost 

 wholly concealed by overlying beds of conglomerate, composed entirely of frag- 

 ments of old red sandstone and mountain limestone. At Winscombe the sand- 

 stone is partially exposed, 1st, near the church ; 2dly, further to the south, imme- 

 diately beneath the escarpment of mountain limestone, the interval being filled 

 by conglomerate. [PI. XXXH. fig. 3. B.] To the east of the road from Bris- 

 tol to Cross the sandstone rises into a bold hill, distinguished by a clump of firs 

 on its summit; and soon afterwards, near Shipham, swells into the ridge of 

 Blackdown, the loftiest in the whole Mendip chain, being 1092 feet above the 

 sea. Blackdown extends about 4 miles in length, from Shipham eastward to 

 nearUbley Hill farm, and is about 1 mile in breadth. In the Roborough de- 

 file the conglomerate rises high up the northern slope of Blackdown, and rest- 

 ing on the edges of the sandstone, presents a bold range of crags on the 

 western side of the ravine. [PI. XXXII. fig. 3. A.] 



* On the side of this valley is a cavern called " the Lamb Cavern," mentioned by many writeu. 

 It is ii >t now open, but appears from the description of it given in Maton's Western Tour (see 

 vol. ii. p. 132.) to be rather an old mine than a natural cave. 



