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subsiding sea-bottom and raised again with a tolerably uniform movement 
over large tracts, with local exceptions, such as are exhibited in the 
railway cuttings at Bourton and Uphill. It is uncertain whether the 
Upper and Middle Lias ever extended to our immediate neighbourhood, as, 
for instance, to Ashley, Cotham, and Bedminster, where the Lower Lias 
is now at the surface. The tendency of the Jurassic series, as is well 
known, is to retreat towards the south-east, but local exceptions to this 
rule ara numerous, and are the result of denudation on a large scale in this 
district. The sequence of the events which effected these results is 
difficult to make out. Great waste must have occurred on the last rising 
of the Palaeozoic Strata before the deposition of the succeeding series, 
resulting in the extensive masses of conglomerate known as Magnesian or 
Dolomitic. The two upper members of the Trias, if ever present here, 
were removed before the deposition of the Lower Lias, and in like manner 
the Upper and Middle Lias, before the commencement of the Oolitic series. 
As the land emerged during this process, the Severn may have begun or 
resumed a passage through the plain in its present channel. Subsequent 
sinkings and risings effected the deposition of the Lower Oolite and further 
denudation until the surface assumed its present form. 
The marks of denudation are various. Perhaps the most conspicuous 
evidence is in the cliffs of our sea shores. Their abrupt termination 
towards the sea shows how the beds have been worn away by the action 
of the waves. The needles and pillars of rock standing here and there at 
a little distance from the coast are further evidences that strike the most 
casual observer. To these may be added natural arches and caverns in 
the cliffs of the sea-shore. In inland districts, long lines of cliffs as well 
as isolated rocks are proofs of the former presence and denuding power of 
some ancient sea. The matter resulting from such denudation is found in 
the boulders, shingle, and sand of our shores, in the conglomerates of the 
geologic series, and the clays and gravels so widely spread over the surface 
of the earth. 
Besides the marks already alluded to, I may mention repetition of the 
beds of the series in a section, groovings and striations in rocks, the 
borings of mollusca, and parallel terraces on hill-sides. Two series of 
the latter are well seen on the isolated hill of Brent Knoll near High- 
bridge, as well as one large platform half a mile wide near the middle of 
the ascent. 
The class of agencies called sub-aerial must be referred to. These 
are silently but surely changing the surface of the dry land in every inland 
