ON THE TRIASSIC ROCKS OP SOMERSET AND DEYON. 367 



40. On the Triassic Books of Somerset and Devon. By W. A. E. 

 Ussher, Esq., E.G. S., of the Geological Survey of England and 

 Wales. (Head June 7, 1876.) 

 (Communicated by permission of the Director of the Geological Survey.) 



Contents. 

 I. The Mendip Area. 

 II. Polden Hills, Bridgewater and Taunton Vale. 

 III. West-Somerset and Devon Area. 



Introduction. 

 The Triassic areas of Devon and Somerset may be divided into three 

 lithological districts : — the first, on the north and north-east of 

 the Polden Hills ; the second, on the north-east, east, and south- 

 east of the Quantocks ; the third, comprising the rest of the 

 Triassic area, lies between Watchet and the south coast of Devon, 

 being bounded on the west by the Devonian and Culmiferous high- 

 lands, and on the east by the Quantock and Blackdown ranges. 



The first of these districts is too well known to call for more than 

 a general description in this place. In the Geological-Survey Memoir 

 on the Bristol Coalfield it has been already treated of, the labours of 

 Conybeare and Phillips, De la Beche, and the late Mr. Wm. Sanders, 

 with those of Messrs. Moore and Etheridge having left little to be 

 desired as far as the description of the Triassic strata is concerned. 

 With reference to the last-mentioned districts, of which we purpose 

 to give a more detailed though far from exhaustive description, it is 

 different, the relations of the Trias not having been before estab- 

 lished, except so far as might be inferred from a study of the 

 sj)lcndid section along the coast between Seaton and Torquay. 



Sir Henry De la Beche, in his report upon the geology of Devon 

 and Cornwall, gives a very general description of the Trias, without 

 attempting a classification of its component marls, sands, and con- 

 glomerates, which the greater time occupied iii the resurvey of the 

 district has enabled me to make, and, by the kind permission of the 

 Director of the Geological Survey, to lay before the Society. A 

 general description, adducing only such evidence as becomes neces- 

 sary to prove the sequence which we have adopted, and to the 

 exclusion of such details as must be reserved for Geological-Survey 

 publication, is here attempted. 



I. The Mendip Area. Trias North of the Polden Hills. 



Throughout the districts occupied by Triassic strata between 

 Bristol in the north and Glastonbury and Shepton Mallet in the 

 south, and between the mouth of the Severn in the west and 

 Erome in the east, their lithological characters seldom vary, the 

 major part consisting of red and greyish green marls, in the 

 neighbourhood of Palaeozoic hills resting upon or dovetailing into 

 conglomerates with a dolomitic matrix, which from their marginal 

 nature are but locally observable and superficially occupy a very 

 limited area. 



Q. J. G. S. Ts T o. 128, 2 d 



