LOWER LIAS. 265 



The clay-bands are in great part represented by slaty marls. These 

 beds belong to the zone of Ammonites planorbis. At Pylle, north of 

 Pennard Hill, beds with A. Bucklandi, etc., are exposed. 



The Lower Lias of Shepton Mallet presents many features of 

 interest. The ordinary limestones and clays are well exposed in 

 the cutting of the Great Western Railway, about a mile west of the 

 station, and again in the cuttings of the Midland Railway south of 

 the new station. Northwards a gradual change takes place in the 

 beds, the clays die out, and we find the series to comprise sandy 

 limestones and occasional conglomerates, formed of Carboniferous 

 Limestone and chert pebbles, indicating that hereabouts was an 

 old sea-margin. These beds, which are seen at Bowlish and 

 Downside, are identical with the Lias conglomerates of South 

 Wales, described by Sir H. T. De la Beche.^ At Downside we 

 find a brown and white granular limestone with irony specks, over- 

 lying the Carboniferous Limestone, to which it sometimes so 

 closely approximates that it is difficult to distinguish between 

 the two, while at this locality and also at Bowlish there is a soft 

 thickly-bedded, white shelly-limestone, from which the shelly 

 matter has frequently been removed, leaving cavities. (See Fig. 

 24, p. 160.) 



A peculiar siliceous deposit occurs in the neighbourhood of 

 Chewton Mendip, on Harptree and Egar Hills, at East End, 

 Emborrow, and near Binegar. It reposes indifferently on the 

 Dolomitic Conglomerate, the Carboniferous Limestone, and the 

 Old Red Sandstone. The deposit is, in the upper part, a compact 

 chert, containing shells ; lower down come sandy beds, and 

 here a cherty breccia occurs. The entire deposit must in 

 places attain a thickness of at least thirty feet, and it is well shown 

 in a pit east of the Harptree Road, about half-way between East 

 Harptree and the inn known as the ' Castle of Comfort.' The pit 

 is about sixty feet in diameter at the mouth, it is funnel-shaped, about 

 twenty to thirty feet in depth, and is probably a natural " pot-" or 

 " swallow-hole." The section consists almost entirely of massive- 

 bedded chert, occurring in layers of from one to three feet in 

 thickness, separated by thin ochreous clayey beds an inch or two 

 in thickness, and standing out sharply, but sometimes weathering 

 sandy at the exterior. Lower Lias fossils occur in the top beds, 

 while very probably the lower beds represent the White Lias, but 

 from these no fossils have been recorded. Among the fossils are 

 Ammonites planorbis, A. Johnstoni, Cardinia Siittonensis, Lima gigantea, 

 Alodiola rnijiima, Ostrea Liassica, Myoconcha psilonoti, and Pecten 

 polliix (or Siittonensis^? Some of the Druidical Stones at Stanton 

 Drew, near Chew INIagna, are formed of cherty beds from the Lias 

 and Keuper of this neighbourhood. (See p. 232.) 



In the Radstock Coal-district, as Mr. C. Moore has pointed out, 



^ Mem. Geol. Survey, vol. i. p. 276. See also Moore, Q. J. xxiii. 508. 

 "^ Geol. East Somerset (Geol. Surv.), p. 108 ; G. Mag. 187 1, p. 400. See also 

 T. Weaver, T. G. S. (2), i. 364 ; Buckland and Conybeare, Ibid. 294. 



