George Clinch—Sculpturings of the Chalk Downs. 53 
it is a mechanical or a chemical deposit; but, I think, the study of its 
phenomena in connexion with the dry valleys of the Chalk tends to 
show that it was due to mechanical rather than chemical agencies. 
It lies mainly on the table-lands of the Chalk, and is rarely found in 
the valleys except in a re-arranged condition or as rainwash. 
The extreme probability that its material was derived in the first 
instance from the dissolution of the Chalk does not, I submit, militate 
against the possibility of its subsequent re-arrangement by mechanical 
agencies. 
The presence of clay-with-flints on the Chalk plateau and its 
absence from the valleys are points well shown in Kent. A good 
example to the east of the River Darent has been figured in one of the 
admirable papers of the late Sir Joseph Prestwich.* 
River Systems. 
It will not be necessary, for the present purpose, to go deeply or 
fully into the river system of the Weald; but the fact that many of 
them flow through channels which cut transversely through the Chalk 
Downs, both north and south, is important as pointing to a very early 
system of watercourses which drained not only the Wealden area as 
we know it, but the Wealden dome before it was bereft of its Chalk 
and Tertiary beds. 
The valleys of the Wye, the Mole, the Medway, the Cuckmere, the 
Ouse, the Shoreham River (now called the Adur), and the Arun are 
broad and important. The Darent Valley is less marked. That of 
the Wandle is well-defined, but dry in its upper part, having had its 
catchment area cut off by the rapid development of the Gault valley. 
The old valley of the Ravensbourne, the main part of which is now 
dry, goes quite as far south as the Chalk escarpment, and probably once 
drained a small part of the Wealden dome. The chief point of interest 
of all these valleys is that they run transversely to the lines of the 
Chalk ridges, and point to an ancient drainage system. 
The fact that the gravels in these valleys contain materials brought 
from the Wealden side of the Chalk escarpment is another of the 
interesting points in their geological history. 
THEORIES ON THE DENUDATION OF THE WEALD AND THE FoRMATION 
oF VALLEYS. 
The papers ‘‘ On the Anticlinal Line of the London and Hampshire 
Basins”, by Peter John Martin, F.G.S., are of great value. They 
are, in fact, a storehouse of information to which Lyell and many 
subsequent writers have turned for inspiration and facts. Martin’s 
papers were published in the Philosophical Magazine in 1851, 1854, 
and 1857, but they deal with observations made as early as 1828. 
After discussing the various phenomena of the Weald, he writes :— 
Ba To conclude: the obvious inferences to be drawn from what we have seen are 
these :— 
“* Since the deposition of the tertiary beds a great and sudden upheaval of some 
parts, and perhaps contemporaneous subsidence of others, took place over a widely 
extended area ; perhaps over the greater part of the South of England. 
1 Q.J.G.S., vol. xlvii, pl. vii. See also Jukes-Browne, ibid., vol. Ixii, p. 132. 
