50 . UEPOiiT — 1875. 



An able paper on this subject, with Map and Sections, by my friend Mr. Etheridge*, 

 F.E.S., will be found in the papers of the Cotteswold Club. 



Dohmitic Conijlomerute. — ^Veayer described this formation as composed princi- 

 pally of " rounded aud angular fragments of limestone exceeding the size of the 

 head, with fragments also of quartz aud hornstone. These are all cemented together 

 by a calcareous paste, which is frequently of a marly natirre — or of a carbonate of 

 lime either of an earthy or compact structure ; " the cement is generally magnesian, 

 and in this there are many cavities frequently lined with crystals of calcareous spar 

 and quartz, and also with the sulphate of strontian. 



This remarkable formation forms a land of iiTegidar broken fringe, hanging on 

 the flanks of the older rocks, and resting unconformably upon them. We shall 

 meet with this conglomerate again in connexion with the beds in the Mendip Hills 

 aud in the Clifton section. 



New Red Sandstone. — The upper aud central members of the New Red Sand- 

 stone arc found near Tortworth ; they consist chiefly of red clay and marl. 



Avicida-contorta beds have been found by the Earl of Ducie in the form of the 

 Boue Bed, the series resting on the inclined edges of the Carboniferous Limestone. 



2. Mendip Hills. 



The Mendip Hills proper extend from Bleadon Hill near Hutton on the west, to 

 Elm and Whatley on the east ; and they strike nearly due west and east, and are 

 about 30 miles in length, with an average breadth of 5 to 6 miles. They constitute 

 the southern base of the Bristol Coal-field, or the base of an almost equilateral tri- 

 angle, formed b}^ the Pala30zoic rocks, comprising the area from Burton Passage and 

 Tortworth to the south slopes of the Mendips ; this includes the outlier Bream 

 Down, which is only a westerly prolongation in the Severn, separated from the 

 main range of the Mendips by the alluvial flat of the estuaiy of the Axe. 



The Lithology of the Mendips consists of Old Bed Sandstone, Carboniferous 

 Limestone, and Trias, the latter represented chiefly by the Doloniitic Conglomerate, 

 which lies unconformably on the Old Red and Carboniferous, flanking nearly the 

 entire range of hills, and in places capping their summits. 



Numerous islands of Carboniferous Limestone surrounded by Triassic rocks occur 

 east of Wells and south of Croscombe, also encircled by fringes of Dolomitic Con- 

 glomerate, of which Church HiU, "Worminster, and Ivnowl-foot Hill are examples ; 

 these outliers testify to the southern extension of the Carboniferous Limestone 

 beneath the New Bed S.andstone and Lias south of tlie Slendips, and lend us aid 

 in determining the probable position of deep-seated Coal Measures similar to those 

 at Vobster, Colford, Edford, Ilolcombe, &c., north of the Mendip range. 



The lower flanks of thenorthern portion of the range are covered by the New Red 

 Sandstone, that of the south being a mere strip traversed by the Wells-and- 

 Axbridge Eailway, the peat plains and bogs of Sedgmoor covering them up to a 

 certain level to the east of the meridian of Glastonbury. The Lias occupies an ' 

 extensive plain, masking likewise the older rocks beneath. 



Old Red Sandstone forms the oldest stratified rock, and is, strictly speaking, 

 the axis of the Mendip Hills. It is exposed in four well-marked areas along the 

 highest ridge :— (1) Blackdown ; (2) North Hill and Pen Hill; (.3) Beacon Hill ; 

 and (4) Bownhead Common, wliich is the largest exposed tract. The intervening 

 areas are occupied by a mantle of Carboniferous Limestone, which arches over and 

 covers the underlying Old Red, denudation having yet spared the limestone. 



The Old Red is exposed along two anticlinal axes, these being, indeed, the chief 

 cause of its exposure ; the axes being post-Carboniferous and pre-Triassic, are not 

 traceable beneath or where the patches of Dolomitic Conglomerate and cherty 

 Lias cover up the Old Red Sandstone and Carboniferous Limestone, as at Harptree 

 Hill, Rowham, Shipham, &c. 



The most northerly anticlinal brings up the fine range of Blackdown, on the north, 

 south, aud east of which occur the Lower Limestone Shales resting on Old Red. 



The northern dip of the anticlinal is higher than the southern, being in places 

 as high as 54° in the north, whilst in the soutli it does not exceed 20°. This anti- ' 



* Proceedings of tlic Cotteswold NaturaHsts' Field Club, p. 28 (18G5). 



