Chap. XX.] 
POWEE OF FOEMEE DENUDATION. 
493 
water could have removed every fragment of the debris that must have 
resulted, whether at one or several periods of elevation, from the destruc- 
tion of all the once superposed arches of rock, and have scooped out all the 
detritus arising from such destruction, from the circling depressions, the 
central dome, flanking ridges, and former cover of those Silurian strata ? 
And if that water had not been impelled with great force, caused by sudden 
uprises of these rocks from beneath the Old Red Sandstone, what other 
agency will account for so complete a denudation, the broken materials 
having only found issue by one lateral gorge, which was, we see, opened 
out by a great transverse fracture of the encircling ridges ? 
The same reasoning, I may add, is applicable to the grander denudation 
of the great valley of the Wealden of Kent, Sussex, and Surrey — a tract 
which I have explored for many years, and concerning the denudation 
of which I have formed opinions entirely differing from those of Lyell and 
Darwin. The former, exhibiting sketches of the escarpments of the 
North and South Downs, infers that they have been cliffs which were 
gradually eroded by waves of the sea. Adopting this view, Mr. Charles 
Darwin (« Origin of Species,' 1st edit., 1859, p. 287), logically estimates that 
the mere erosion of the sides of the Wealden Valley, according to the 
ordinary rate of wear-and-tear of wave-action, must have been a pro- 
cess lasting not less than three hundred million years ! 
Now I affirm that there is no proof whatever that the waves of the 
sea ever beat against or wore away the escarpments of either the North or 
South Downs ; for if such had been the case, we should surely, somewhere 
in the great circuit of the chalk-cliffs which subtend the Wealden area for 
a distance of 160 miles, be able to detect some evidence of such shore-action, 
whether it took place during the latest Tertiary or at any subsequent 
periods. Gravel-beds formed by the action of breakers, whatever may be 
the date of their formation, are always clearly distinguishable by their 
rounded condition from all other kinds of drift translated by water. Such 
pebble-beds formed by waves of the sea are beautifully exhibited in the Ter- 
tiary strata at Woolwich and Blackheath, extending to Addington Heath, 
near Croydon; and pebbles similarly formed are seen in various raised beaches 
of more recent age around the coasts of Britain. In all these cases the 
pebbles are just like the shingle now rounded on the shore. But not a trace 
of such shore- action is to be detected at any level, at the foot or along the 
sides of the escarpments of the North and South Downs. In place of this, 
we there only find local heaps of angular and broken flints, the relics 
the debris arising from the destruction of the dif- torily the great extent of erosion ; and when we 
ferent Silurian rocks within the ellipse, I made see that excavation has proceeded so far as to 
this observation: — "When, however, we reflect groove the broad channels which surround the 
upon the nature of the elevation, we see in it the central dome and to carry away large portions of 
inevitable result of the sam-i powerful operations the associated (Silurian) rocks, why should we 
that have produced the form of the valley ; for expect to find a trace of the wreck of the once 
whether we embrace the hypothesis of a sudden overlying strata (Old Eed Sandstone) which must 
expansion or of a number of shocks, we are com- have been removed before the work of denudation 
pelled to call into play the action of currents, both could commence upon the inferior deposits." 
violent and long continued, to explain satisfae- (' Silurian System,' 1839, p. 436.) 
