South-western Coal District of England. 229 



however, the lias, based occasionally on red marl and its conglomerate, is pro- 

 longed from the platform which it forms at Shepton Mallet to the very foot of 

 the sandstone ridge of Penhill, and partially conceals on that side the calca- 

 reous zone. [PI. XXXII. fig. 2. and fig. 2. A.] This mass of lias forms a 

 narrow strip more than 3 miles long, which extends from Crapnal farm near 

 Cross Combe, on the east, by Chilcot, East Horrington, and Birrel farm, to 

 Milton-house, near Wokey. Its western portion fills a hollow bounded partly 

 by old red sandstone and partly by mountain limestone, and may be seen on 

 the road after ascending about one-third of the hill above Wells. The moun- 

 tain limestone protrudes itself to the south of the lias in Stowborough and 

 Milton hills. 



To the west of East Milton the dolomitic conglomerate ascends the hills to a 

 considerable height, around the ravine which terminates in Wokey hole, which 

 cavern, and the chasm which immediately leads to it from below, are formed 

 in that conglomerate. About half a mile west of Wokey hole, a fine combe 

 appears, flanked by mural precipices of mountain limestone, and known by the 

 name of Ebber Rocks. 



The tract to the north of Penhill consists of a table-land of mountain lime- 

 stone, which presents no remarkable feature, but serves to separate Penhill 

 from the northern nucleus of old red sandstone. [PI. XXXII. fig. 2, A.]. 



The 3d or northern nucleus of old red sandstone is loftiest at its western 

 extremity to the north-east of Priddy. This is the most conspicuous summit 

 in the central part of the Mendip chain, and is called sometimes North Hill, 

 and sometimes Eight-barrow or Nine-barrow Hill, from two groups of sepul- 

 chral tumuli on its surface. Prom North Hill the ridge of sandstone sweeps 

 eastwards about 3 miles, following a curve-line concave towards the north, 

 until it approaches a farm called Tar Hall, where a deep valley, descending 

 towards Chewton Mendip, intersects it. [PI. XXXII. fig. 2. A.] To the north 

 of this valley the sandstone re-appears in Egar Hill, and there terminates. 

 These sandstone eminences, when viewed from the calcareous table-land 

 on the east of Tar Hall, which is there unusually depressed, appear very 

 bold and striking. The height of the summits on either side of the Tar Hall 

 valley is increased by a covering of a remarkable shelly chert, which we shall 

 have occasion to notice in our description of the overlying rocks. 



The band of mountain limestone, lying on the northern flank of this 3d 

 nucleus of sandstone, is much concealed by overlying deposits. Its hangings 

 above the valley of Chewton Mendip and the two Harptrees, are covered by the 

 dolomitic conglomerate. The conglomerate also forms an upfiUing in the 



