1870.] ETHERIDGE—BRISTOL DOLOMITIC CONGLOMERATE. 179 
limestones of the N.E. of England. At Yate Rocks, near Yate and 
Chipping Sodbury, the yellow conglomerate, similar in all its con- 
ditions to that of Clevedon, rests upon the upper beds of the Carbo- 
niferous Limestone and Millstone Grit, assuming the most step- 
like character (c in fig. 1). The edge of the underlying limestone, 
(a), is denuded to a perfect plane by the agent which deposited the 
conglomerate. 
Fig. 1.—Section at Yate Rocks. 
6 & e, Conglomerate. 
This locality exhibits the only remnant of the yellow magnesian 
beds known in the northern part of the Bristol coal-field. They must, 
however, have extended along the whole of the eastern side of the 
basin, from Wick Rocks to Cromhall, where a similar solitary patch 
attests its northern extension. North of Cromhall, at Tortworth, 
the conglomerate follows the curve and strike of the Old Red Sand- 
stone and Lower Limestone Shales. I cannot doubt that the yellow 
beds of Yate Rocks might be exposed in many other places by the 
removal of the Trias and overlying Lias. 
4. GnogRAPHIcAL DistRIBUTION or, oR AREA OCCUPIED BY THE DoLo- 
mitic CoNG@LOMERATE. 
The paleozoic rocks of the Bristol coal-field, ranging in time 
from the Caradoc sandstone to the close of the coal-measures in- 
clusive, are more or less indiscriminately covered by patches of this 
conglomerate at various heights, from 20 feet to 350 feet above the 
level of the sea. These rest either upon the Silurian, Devonian, or 
Carboniferous series, and are the result of that marine denudation 
which took place during the later Bunter or the commencement of 
the Keuper deposits. 
The Bristol coal-basin occupies an area of about 600 square 
mailes, or a tract of country 30 miles long by 20 wide; and every- 
where within this area, either fringing or capping at intervals the 
oldest rocks, does the dolomitic conglomerate occur. 
Its northernmost limit is at Tortworth; and its most southerly 
extension is outside the limits of the basin, or south of the Men- 
dips, at Worminster and West Compton, the whole equalling a 
distance of 32 miles, and haying masses more or less exposed 
along the whole western side of the coal-field. The north and 
south flanks of the Mendips are both continuously fringed and 
partly covered by beach-like masses varying from 20 to 50 feet in 
thickness, and in places ascending to the very summit of that range 
of hills, as at Shipham, North Hill, and Haydon, at Blagdon, East 
