TBANSACTIONS OF SECTION C. 719 



In this shallow strait the clays and sands were deposited, and just such an 

 assemhlage of mollusca is found as will bear out this view. Scarcely any of 

 the shells which are of li\-ing species are known to inhabit such deep water as Mr, 

 Keid indicates, while the majority show the presence of a laminarian zone, ex- 

 tending to not more than fifteen fathoms. This bathymetrical range is the chosen 

 habitat of the Eissofe, who are all vegetable feeders, and of the Nassas, which 

 are predatory and always plentiful just below low-water mark ; and what appears 

 still more conclusive is the number of Hydrohias, which have a close connection 

 with Littoriua, and indicate shallow depth and close proximity to shore. 



It is hoped that a more detailed examination of the molluscan fauna may soon 

 be completed, and the whole series added to the national collection. 



11. Report on the Higher Eocene Beds of the Isle of WigJit. — See Reports, 



p. 414. 



WEBXESDAY, SEPTEMBER 7. 

 The following Papers were read : — • 

 1. The Triassic Bodes of West Somerset. By W. A. E. Ussher, F.G.S. 



This paper forms a necessaiy supplement to a series of papers on the Triassic 

 rocks of Devon, Somerset, &c., communicated to the Geological Society by the 

 author in the years 1876, 1878, and 1879. In the first two communications reference 

 was made to the probable existence of Infra-keuper beds in the area between 

 Williton and Porlock, inferred from a brief visit. This opinion was given 

 with some reservation ; it would entail the existence of a considerable fault which, 

 not then being able to study the Devonian rocks of the area, the author was 

 unable to verify. 



The present contribution is the result of subsequent investigations, made in the 

 years 1878 and 1879. The constitution, extent, and general relations of the 

 Lower, Middle, and Upper Triassic rocks of the area are briefly described seriatim, 

 with the following general results : — 



The Lower Trias consists of breccia and breccio-conglomerate upon sands and 

 brecciated sand and loam ; it occupies the east of the valley, extending from 

 Lydeard St. Lawrence northward to Yellow Wood Farm, south of Sampford 

 Brett, where it finally disappears, being faulted against Keuper basement beds 

 and conformably overlapped by Middle Trias marls upon the margin of the older 

 rocks. 



The Middle Trias, consisting of marls with sandstones in places at their base, 

 occupies the centre of the valley, being faulted against the successive divisions of 

 the Keuper on the east, and terminating northward in the angle made by con- 

 vergent faidts at BicknoUer. The jNIiddle Trias marls rest on the older rocks near 

 Yellow Wood Farm, and finally disappear near Orchard Wyndham, south of 

 Williton, under Keuper breccias. 



The Keuper beds consist of marls, sandstones, and a locally varying series of 

 conglomerates, gravels, and breccia in descending sequence, the sandstones are 

 very calcareous south of Crowcombe ; they form" marginal deposits in places near 

 Dunster. In the Porlock valley they constitute an insignificant horizon, and at 

 Sampford Brett have local intercalations of marl at their base. 



The coarser beds of the Keuper develop at the expense of the sandstones in the 

 area west of Williton. In the form of incoherent gravels they constitute outliers 

 on the Middle Trias marls. The massive conglomerates occur locally to the 

 north of Crowcombe Heathfield station. Near Beggearn Huisb, and in the 

 Porlock valley, the Keuper basement beds resemble varieties of Lower Trias 

 breccias in the Tiverton area, having been deposited under analogous conditions. 



