George Clinch—Sculpturings of the Chalk Downs. DT 
Downs as due to the erosive action of water, have not, I think, given 
sufficient importance to the fact that Chall, of all rocks, is peculiarly 
_ sensitive to the disintegrating influence of frost, particularly when 
the beds are heavily charged with water. The effects of a frost may 
be seen, when thaw sets in, in every chalk-cutting and chalk-pit. 
What its effects may have been when these valleys were half-filled 
with water and the temperature fell very low, it is difficult to realize 
at the present time; but the work that was accomplished by alternate 
freezing and thawing is to be seen in the valleys of the Chalk Downs, 
many of which are eaten back by the disintegrating and disrupting 
frost into intricate and complicated forms. In some cases this erosion 
has been carried to the extent of breaking down the divisions between 
adjacent valleys, and the formation of isolated hills, (See Fig. 1.) 
The suggestion I make, then, is that the chief eroding agent was, 
not the waves and tides of the sea as some have suggested, nor the 
‘running water’, nor the ‘mountain-torrents’ of others, but the 
frost itself acting upon Chalk charged or saturated with water.' 
By this means, I suggest, the valleys were cut back into the Chalk 
Downs, the development being to a large extent lateral. The frost 
was most active, I suggest, where the Chalk was wettest, and the 
waters standing in the valleys half-choked with ice provided precisely 
the necessary condition to produce the maximum breaking-up of the 
Chalk. 
I have spoken of the relatively small size of the catchment-area as 
compared with that of the valleys. It had, to me, long been an 
enigma; but with the explanation I offer, I think, the difficulty 
disappears, because the eroding forces were contained in the valleys 
themselves when the Chalk below was impervious and they were 
partly filled with water. The wet condition of the Chalk may have 
arisen from partial thaw and not wholly from rainfall. 
At the same time it must be borne in mind that the condition of 
semi-saturation, under which the frosts were most destructive to the 
Chalk, was most naturally produced when there was some kind of 
catchment basin. Indeed, it would seem that such a basin was 
absolutely necessary to produce the requisite conditions, because 
when the valley was cut back quite near the edge of the Chalk 
escarpment, and the drainage became insignificant, the hollow channel 
dies out. 
The transporting agencies of floating ice, and the floods arising from 
the periodical breaking-up of the ice-masses in the valleys would 
doubtless be sufficient, in the case of the steeper valleys or coombes, 
to sweep the debris down into the sea or into the valley or estuary of 
the Thames. 
The whole of the phenomena of the Dry Chalk Valleys and other 
forms of sculpturings of the Chalk Downs may, I submit, be amply 
accounted for by the forces I have attempted to describe; and if, as 
seems obvious, the valleys be closely related to the denudation of the 
Weald, it is perhaps within the region of probability that the latter 
may have been influenced by the same cause. 
1 On this subject see remarks by S. V. Wood, jun., Q.J.G.8., vol. xxxvili, p. 718. 
