52 REPORT — 1875. 



end. The entire range of the Mendips is surrounded by Dolomitic Conglomerate ; 

 and ten or twelve patches still remain as unconformable undenuded masses of that 

 formation resting upon the older rocks forming the massive range of the Mendips. 

 This remarkable deposit completely covered the range when at a lower level, its 

 partial removal being conclusively shown by the remnants that still cling to the 

 steep face of the northern and southern flanks of the Mendips. 



This Conglomerate is composed entirely of greater or lesser fragments of the older 

 rocks composing the hills, and is the result of the denuding action of the sea that 

 deposited the Keuper Beds. This marine denudation took place when the entire 

 area occupied by the Mendips and Coal-basin underwent depression, the Dolomitic 

 Conglomerate and sandstones accumulating ^;ro rata with the depression and con- 

 sequent destruction of the rocks offered for resistance. This conglomerate, the " over- 

 lie" of the coal-miners of the Bristol basin, although visible only upon the Palaeozoic 

 rocks surrounding the coal-bearing area, is nevertheless entirely spread over them, 

 and beneath the New Red Sandstones that occupy nearly the entire area from Tort- 

 worth to the southern flanks of the Mendips, its presence being marked by the marls 

 and sandstones of the Keuper, the Lias limestones, and in other places the Oolitic 

 rocks that lie within the Coal -basin, especially along its south-east border from Bath 

 to Wells. We have no physical evidence more convincing of denudation, elevation, 

 and depression over large areas of the earth's surface than what we can witness so 

 easily and study so advantageously in the Mendip Hills ; for this conglomerate 

 rock here defines the limits between Mesozoic and Palaeozoic times : the highly 

 inclined Old Red Sandstone forms the nucleus of the chain, the Carboniferous rocks 

 resting upon it ; and the Coal Measures in conformable succession to the latter were 

 all indurated, metamorphosed, elevated, and thrown into folds long prior to the time 

 •when, under slow depression, destruction, and denudation, the Dolomitic Conglo- 

 merate was laid down by the Triassic Sea — the resultant of wave forces along 

 a coast-line which was then the Mendip range, its shingle and boulders being slowly 

 cemented by a magnesio-calcareous paste derived from the wasting beds of the 

 great limestone series. For further details regarding the natural history of the Dolo- 

 mitic Conglomerate I must refer to a valuable memoir on this formation by Mi". 

 Etheridge, F.R.S.* 



The Rhcetic. — Singular beds of cherty and sandy deposits of Rhsetic age occur in 

 several parts of the Mendips, in places brecciated, or as a conglomerate, and resting 

 either upon the Dolomitic Conglomerate or Carboniferous Limestone. 



The fossils are either cherty, or they have been removed, and their moulds are 

 formed of chert, or cavities are left where organisms existed. 



These beds are exposed at East Harptree, Egar Hill, Ashwick, and Shepton- 

 Mallet. In the Vallis they repose immediately on the upturned edges of the Car- 

 boniferous Limestone, and even fill in the numerous veins, pockets, and faults in that 

 formation with fossil species common to the beds. 



Nowhere can the geologist read more clearly the physical history of the groups of 

 associated rocks composing the structure of the Eastern Mendips than at Wells, 

 the Vallis, Watley, Elm, Nunny, and Holwell, where Old Red Sandstone, Car- 

 boniferous Limestone, Coal Measures, Dolomitic Conglomerate, Rhsetic Beds, Lias, 

 and Oolites are all exposed in natural sequence to each other. There can be 

 no doubt that the Rhsetic Sea surroimded and covered the Mendips ; for its remains 

 are found reposing on the Old Red Sandstone, Carboniferoiis Limestone, Coal Mea- 

 sures, and Dolomitic Conglomerate, and pass upwards into the Lias beds. 



The Lias. — Fragmentary portions of this formation are found resting upon the 

 summits of the Mendips, covering respectively Old Red Sandstone, Carboniferous 

 Limestone, Dolomitic Conglomerate, and Rhsetic beds, and in the Holcombe and 

 Barrington districts resting upon the Coal Measures, proving the former exten- 

 sion of the Liassic Sea over the Mendips ; for upon some of their highest points, as 

 near as Castle Comfort, the cherty beds, with their characteristic fossils, are found ; 

 also at Chewton Mendip, Emberrow, and Ashwick, &c. ; and on the south side of 

 the hills it is found at a considerable height, as at Downside, Chilcott, and West 

 Herrington. During the Lias age the Mendips must either have been an archipe- 

 jago, or they Were totally submerged beneath the sea which deposited the Liassic 



* Quart. Joum. Geol. Soc. vol. xsvi. p. 174 (1870). 



