CARBONIFEROUS LIMESTONE. l6l 



and Cleve Combs afford opportunities for studying the Carboni- 

 ferous Limestone, amid very pleasant surroundings. (See Fig. 2, 

 p. 14, p. 30, and Fig. 24.) 



The islets known as the Steep and Flat Holmes in the Bristol 

 Channel are formed of Carboniferous Limestone. Both islets 

 exhibit an anticlinal structure in the Limestone, and in the Steep 

 Holme the anticlinal appears to be inverted. West of Dolberry 

 Camp the Limestone exhibits a ' fan-shaped ' structure, which may 

 be simply the result of a synclinal, but possibly it may be connected 

 with this apparently inverted anticlinal in the Steep Holmes. 



Several isolated masses of Carboniferous Limestone in the 

 neighbourhood of Luckington and Vobster, near INIells, on the 

 northern side of the Mendip Hills, have attracted attention. They 

 appear to rest on the Coal-measures, which have at one or two 

 points been proved beneath the Limestone. Mr. J. McMurtrie 

 considers these masses of Limestone to have been folded 

 over from the Downhead anticlinal of the Mendip range. The 

 physical structure is, however, opposed to this inversion, and 

 the occurrence of the Limestone masses is better explained by a 

 local faulted anticlinal structure.' A section opened at the west 

 end of the Limestone at Vobster, to which I was conducted in 1885 

 by the Rev. George Horner, showed a series of dark shales (Upper 

 Limestone Shales), and Millstone Grit, above the Carboniferous 

 Limestone ; these beds were faulted against the Limestone on the 

 north. This evidence is opposed to the view that the Carboniferous 

 Limestone is here inverted.^ 



In so disturbed a tract of ground as this portion of the Somerset- 

 shire Coal-field, one must interpret the grand earth-movements in 

 a large way, for the numberless contortions and twistings in the 

 Coal-measures themselves are but the exaggerated representatives 

 of great folds in the older and more stony strata. The Lower 

 Coal-measures, for the most part easily squeezed up and crumpled, 

 cannot in themselves explain these phenomena, and therefore a 

 study of the folds that are readily to be traced out in the Carboni- 

 ferous Limestone and in the Old Red Sandstone is very necessary 

 before we attempt to picture the amount of disturbance in the 

 district. Moreover, the structure of the Mendip Hills is not that of 

 one simple anticlinal fold dipping to the north-east and south-west, 

 and trending north-west and south-east ; but the structure com- 

 prises a number of folds, which trend in an easterly and westerly 

 direction, and which are products of that line of upheaval, which, 

 only when looked at in a large way, can be termed the " Mendip 

 Anticlinal." And it is the prolongation of these known disturb- 

 ances into the Coal-measures that must help to account for the 

 great dislocations and contortions that affect them. 



The existence of such Limestone masses in the midst of an 



^ See Memoir on the Geology of East Somerset and the Bristol Coal Fields, 

 p. 196 ; G. Mag. 1871, p. 149 ; 1876, p. 455 ; Proc. Bath Nat. Hist. Club, v. 24. 

 ^ See H. H. Winwood, G. Mag. 1882, p. 238, also p. 286. 



