49 
Deposition takes place mostly during depression, and denudation during 
elevation of the land. Supposing, therefore, these great geological forma- 
tions to have been slowly deposited during a gradual depression of the 
sea-bottom, and upheaval afterwards to begin at various points ; as these 
points reached the surface of the sea denudation would commence, and 
would continue until the debris created a bank sufficiently high to with- 
stand the further advance of the waves, by which time great part of the 
whole amount of denudation may have been effected. The rest may have 
resulted from repetitions of the rising and sinking movement. 
The gorge of the Avon exhibits the phenomenon of denudation on a 
large scale, though it may be admitted that the commencement of the 
chasm was probably due to a violent rupture of the rocks. The rift would 
gradually widen and deepen as the land emerged from the sea, and newer 
strata deposited within the chasm may have been removed during a 
subsequent elevation, many successive risings and sinkings having occurred 
in this locality. Professor Jukes attributes the formation of the gorge 
solely to the river itself, which, existing at a time when the liassic strata 
spread in a vast sheet from Dundry over all the district, deepened its bed 
until it reached the limestone, over the seaward edge of which it poured 
in a cataract, which wore away the rocks backward until it had formed 
the chasm as it now exists. To call in the aid of a river whose existence 
at that period it would be difficult to prove, while the sea, even now near 
at hand, is well known to have many times submerged the whole district, 
appears however quite unnecessary, seeing that the latter is capable of 
forming very deep indentations in rocky coast-lines, such as our carbon- 
iferous cliffs would have then exhibited. If the river existed so long ago, 
it would seem more probable that it reached the sea by the valley of 
Nailsea, until the formation of the Clifton gorge by the united action of 
internal heat and marine denudation, after which it would avail itself of 
the more direct channel. A similar phenomenon, on a smaller scale, is 
exhibited at the mouth of the Eiver Axe in Weston Bay. The sea having 
eaten its way through the rocky barrier once continuous between Uphill 
and Brean Down, the stream, which formerly entered the sea on the south 
side of Brean Down, changed its course and took the new and shorter 
channel into Weston Bay. 
Let us now imagine the hollows of the Palaeozoic Strata, after denuda- 
tion, filled with deposits of the triassic and liassic formations up to th 
Inferior Oolite inclusive. These strata are in our district conformable and 
nearly horizontal, having been probably laid down on a gradually 
