South-western Coal District of England. 303 



half-way up the hangings of the Mendip chain^ and overlying all the interme- 

 diate formations, abuts against the mountain limestone. The northern and 

 most elevated portion of this inclined plain is traversed by several valleys, 

 which partially exhibit the mountain limestone beneath the lias, in those pa- 

 rallel and broken ranges which have already been described in the 2d chapter. 

 The newer red sandstone and the dolomitic conglomerate may be seen form- 

 ing upfillings or hanging masses on the rugged surface of these ranges, 

 wherever the mountain limestone does not rise to a level with the plane of the 

 lias. The principal of these valleys is that through which flows the brook that 

 waters Shepton Mallet, remarkable for its cliffs and beautiful scenery. 



This valley nearly marks the limits of a very remarkable alteration which the 

 lias undergoes ; that portion of it which lies to the north of the valley differing 

 greatly in texture and appearance from lias of the usual character. We here 

 see it in many places serving as a cement to fragments of mountain limestone, 

 and thus passing into a rock which it is often impossible to distinguish from the 

 dolomitic conglomerate. The fragments in this lias-conglomerate are often 

 very large, and sometimes, when they have become decomposed, a singular 

 rock, of a honey-combed appearance, has resulted. From this lias-conglome- 

 rate the organic remains of the lias have disappeared altogether. This con- 

 glomerate constitutes the eastern part, as far as Birrel farm, of the narrow strip 

 of lias which runs from Grapnel farm near Crosscombe by Chilcot and East 

 Horrington to East Milton near Wokey ; in the western part of this strip, from 

 Birrel farm to Milton-house, the lias assumes its ordinary character. As we 

 recede from the extreme boundary of the lias, we find fragments sparingly im- 

 bedded in a cement which abounds with organic remains. This variety ap- 

 proaches in character to the usual forms of lias. It is however of a granular 

 texture, which texture distinguishes indeed all the lias to the north of the 

 Shepton valley. In one remarkable variety there is such an admixture of sili- 

 ceous matter, that the rock, in portions of its mass, becomes a greenish chert. 



On the summit of the Mendip hills, to the west of North-hill, near Hydon 

 farm *, we may observe the remarkable appearance of a patch of lias, at a level 

 far above the ordinary level of the plane of the strata of that formation, and at 

 a spot entirely insulated by other and more ancient rocks. It does not attract 

 attention on the surface, nor would its existence have been ascertained but 

 from the sinking into it of a marl-pit, the organic remains from which are de- 

 cidedly those of lias. Within a furlong, both to the north and south, moun- 



* The exact spot nearly coincides in tlie Ordnance Map with the upper end of the letter I in 

 the word MENDIP. 



•VOL. VI. 2 R 



