178 PROCEEDINGS OF THE GHOLOGICAL SOCIETY. [Jan. 12, 
fuses to accept the fact that scarcely one-fourth of the older rock- 
masses of Somersetshire, Gloucestershire, and Glamorganshire now 
exist in their original conditions ; and a careful study of the pheno- 
mena connected with the deposition and accumulation of the Dolo- 
mitic Conglomerate carries with it the conviction that this area, in 
the West of England, at the close of the coal-measures, on its eleva- 
tion from profound depths, was subjected to great and long-con- 
tinued denudation; and as the old land slowly rose, its original 
mass was greatly reduced by the action of the Keuper sea. 
Prof. Ramsay, in 1846, in his elaborate memoir upon the “ Denu- 
dation of South Wales and the adjacent English Counties” *, in dis- 
cussing the probable presence of the lower members of the New 
Red Sandstone, suggests that these strata were either “ destroyed 
after deposition or were concealed by overlapping upper. beds of 
New Red, which, still resting in a comparatively undisturbed basin, 
may conceal the missing members in hidden hollows.” This hypo- 
thesis is highly probable; but, up to the present time, it has not 
received confirmation. 
We cannot, however, doubt that this conglomerate with its asso- 
ciated sandstone and/marlsy} is part measure of the waste, and the 
result of marine and subsequent subaérial denudation under the 
agency of time; for whateyer inequalities of coast-line or exposed 
masses existed at the close of the paleeozoic period, it was during 
the formation of the conglomerates and breccias that they were 
removed, and the newer masses relatively arranged nearly as we 
now find them, thus furnishing us with data to calculate approxi- 
mately the several levels or heights of the older continent above the 
level of the New Red sea (assuming the latter to have been constant), 
and thus enable us to find the age of the Dinosaurian conglomerate 
on Durdham Down near Bristol. 
The average thickness of the New Red series over the Bristol 
area is about 250 feet, less by one-third than the same series in the 
northern and central part of England. 
The lowest member recognized in the Bristol and South-Wales 
coal-field is the Dolomitic Conglomerate. I may, however, mention 
that in some localities there are no pebbles; for at Sully, on the 
Glamorganshire coast, the rock is perfectly homogeneous, and has 
the appearance of a dolomitized carboniferous limestone, and in 
many places the different conditions of these rocks pass so imper- 
ceptibly into each other that it is convenient to consider them all 
under the common appellation of conglomerates. 
The average thickness of this conglomerate is about 20 feet, 
although many sections exhibit mural faces and slopes 40 or 50 
feet in height or thickness. Occasionally it becomes so fine-grained 
and highly charged with the cementing matter, that it assumes the 
character of a compact dolomite, resembling the yellow magnesian 
* Memoirs of the Geological Survey, vol. i. 
+ The New Red Sandstone formation in this area is composed of three mem- 
bers :—1, the Dolomitic Conglomerate; 2, the New Red Sandstone; 3, the New 
Red Marls at the summit, 
