CARBONIFEROUS LIMESTONE SERIES. 
187 
II. — Relation of the. Carboniferous Limestone Series to the 
other Rocks. 
From the eastern limit of the area in the Avon valley, along 
its northern boundary nearly as far W. as Nash House, the 
Carboniferous Limestone rocks rest conformably on the Old Red 
Sandstone, the shaly K-beds (Lower Limestone Shales) occupy- 
ing a marked depression between the limestone plateau to the 
S., and the irregular but often fairly high country formed by 
the Old Red Sandstone to the N. From near Nash House westward 
to the end of the area the northern boundary is a faulted one, 1 
the Clapton Fault bringing the Coal Measures of the little 
Clapton-in-Gordano Coalfield against the Carboniferous Lime- 
stone. The fault cuts out the K-beds. 
Except for a distance of about a mile near Nailsea, where the 
Coal Measures are in contact with the Carboniferous Limestone, 
the limestone plateau everywhere rises somewhat steeply from 
the Triassic lowland to the south. As is the case elsewhere in 
the Bristol district, the conglomeratic base of the Trias (Dolomitic 
Conglomerate) extends as tongues up the pre-Triassic valleys in 
the limestone, and patches of it are met with high up on the 
plateau, occasionally as to the N. of Tyntesfield farm and in 
the western part of Ashton Park, reaching a height of over 
400 feet. The i-inch Geological Survey map has been in the 
main followed in indicating the position of these tongues and 
patches on the accompanying map. 
Near Long Ashton on the southern boundary, and near 
Clapton-in-Gordano on the northern, small inliers of the Car- 
boniferous Limestone Series appear through the newer rocks. 
III. — Faults. 
The Clapton Fault. — The important fault forming the northern 
boundary of the Carboniferous rocks westward from Nash House 
has already been alluded to. It is shown in the 1 inch Geological 
Survey map and was described by Buckland and Conybeare as 
follows 2 : — 
" The western half of the chain, from Clevedon to near Portbury, 
presents remarkable anomalies along its northern escarpment. The 
local phenomena are such, as clearly indicate that a great fault ranges 
along the edge of this part of the escarpment, affecting a very con- 
siderable subsidence of the strata, so that the coal-measures, depressed 
to the level of the old red sandstone, appear to occupy its place, and 
seem to dip beneath mountain limestone, on which, in fact, they 
repose. The limestone beneath the coal-measures having subsided as 
well as the coal-measures themselves, on re-emerging forms a second 
calcareous ridge, called Walton Down, to the west of Leigh Down 
though not parallel to it The anomalous appearances 
attending this fault are well exhibited in the northern part of the 
1 See following sections. 
2 Trans. Geol. Soc, 2nd ser., Vol. I. (1824), pp. 238-239. 
