64 DR. T. F. SIBLT 0]S^ THE FAULTED INLIEE OF [Feb. 19X2^ 



from the faulted junction with the Grit-&- Shale Mass, the lime- 

 stones are vertical (section, PI. TI). The south-western corner of 

 the quarry, shown in PI. Ill, fig. 1, affords an excellent exposure of 

 the disturbed limestones. Here, apparently, we are on the margin 

 of the greatly- disturbed belt adjacent to the Grit~&-Shale Mass. 



(ii) Western end of the quarry: the summit of the 

 Seminula Zone (PI. Ill, fig. 2). — The lowest beds seen, those 

 lying at the present western extremity of the quarry, are dark-grey 

 compact limestones. Their weathered edges, exposed where the soil 

 had been removed on the brink of the quarry, yielded the following 

 fossils : — 



Froductus afF. giganteiis (Mart.), ' mut. D/ Vauglian ; common. 

 Carcinoiitliyllnm G Yaugbau ; common. 

 KonincJcophyllum aff. Q Vaughan. 

 Syriiigopora of. distans Fischer. 



As to the horizon of these beds, the common occurrence of the 

 two first-named fossils indicates either the summit of the Seminula 

 Zone or the Lower Dibunophyllum Zone. But, since both Dihuno- 

 l^hyllum and CyatJiopliyllum murchisoni, fossils characteristic of D,, 

 appear to be absent, and since the immediately overlying (that is, 

 older) strata undoubtedly belong to S^, the beds in question must 

 be assigned to the top of S,, rather than to the base of D^. The 

 exposed thickness of these beds was about 15 feet. 



(iii) jS'orthern and eastern sides of the quarry: the 

 main Seminula Zone. — The section given by the northern and 

 eastern faces of Vobster Quarry is a very fine one, and by far the 

 most extensive exposure of Seminula Beds to be found in the 

 eastern Mendip area. 



Lithology.^ — The development of dark-grey or black lime- 

 stones, compact in texture and breaking with a conchoidal or 

 splintery fracture, is a conspicuous feature here, as in the Seminula 

 Zone throughout the South- Western Province. Limestones of this 

 general character form most of the western half of the section : 

 with them, in the westernmost part, shaly partings are frequently 

 intercalated. 



Among these limestones the following different types are conspicuous : — 

 {a) 'Horny' limestones, with a perfectly smooth, conchoidal fracture.'"' 

 {h) Very compact but not ' horny' Ihnestones, appreciably crinoidal, and 

 breaking with splintery rather than conchoidal fracture. In these the 

 individual beds often break readily into layers measuring from half an inch 

 to 2 inches in thickness, owing to the development of shaly carbonaceous 

 films at intervals, 



^ Compare the lithology of the main Sonimda Zone in the Eurrington- 

 Combe section, recently described by Prof. S. H. Eeynolds, Q. J. G. S. vol. Ixvii 

 (1911) pp. 344-47, 'Upper Sonimda Zone.' 



^ These are identical with the type of limestone termed ' china-stone " by 

 Dr. A. Yaughan, Proc. Bristol Nat. Soc. ser. 4, vol. i (1904-07) p. 94. They 

 are included in the ' calcite-mudstones ' of Mr. E. E. L. Eixon, Q. J. G. S. 

 vol. Ixvii (1911) p. 51G. 



