WMtaker — On Subaerial Denudation. 485 



thousand times as many will be carried away in a thousand years, 

 other things being equal, and so on. 



Secondly, if the escarpment were an old sea-cliff weathered down 

 into a slope, it ought to show some such section as that in Fig. 1, in 

 which a talus rests against the weathered face of the cliff, only the 

 higher part of the hill being of bare Chalk. But this is not the 

 case ; large pits are common along most Chalk escarpments, and 

 they show a more or less clean face of rock from top to bottom. 

 The supposition that subaerial denudation may have cut back the 

 hill, and destroyed the cliff with its talus and beach, has been noticed 

 before. I question, too, if there is a known case of an old cliff that 

 has weathered to so long and smooth a slope as that of a Chalk 

 escarpment. 



Next let us turn to the country at the foot of the hills, taken up 

 by the flintless Chalk and the underlying beds, What sort of 

 surface-deposit is found there ? is it made up of water- worn pebbles 

 like those on our present shores ? No indeed, but we commonly 

 find, on the contrary, broken and subangular flints, like those of our 

 old river-gravels, sometimes simply scattered over the surface, at 



Fig. 1. — Section of an escarpment on tlie supposition that it is an old cliff. 





a. Talus. 6. Face of old cliff, c. Bare Chalk. 



others abundant enough to form small patches of gravel. In 

 Buckinghamshire there are thin spots of such far out on the wide 

 plain of the Gault. What can these flints be but the insoluble 

 residue of the great mass of Chalk that has been slowly dissolved 

 away, not pounded and worn by the waves ? the remains of which 

 latter kind of process should be looked for rather in such deposits 

 as the old Tertiary pebble-beds of Kent, and the shingle-flats of the 

 south-eastern coast. 



It is not at one spot only that these things may be seen, but more 

 or less along Chalk escarpments generally. In some places too a 

 small stream runs for miles at or near the foot of the ridge : thus a 

 branch of the Mole near Dorking, and a branch of the Stour near 

 Ashford. 



[Whilst the first part of this paper was in the press I was taking 

 a holiday-ramble in the Isle of Purbeck, and noticed there a good 

 and marked example of the fact that the bottom of an escarpment 

 is sometimes at a higher level at one place than the top at another. 

 The level of the Chalk ridge falls westward from Nine Barrow 

 Down to Corfe Castle by three slojDing steps, giving rise to four 

 different levels (not counting the still lower conical hill on which 

 the castle stands), the western of which is lower than the bottom of 

 the escarpment under the higher parts, as shown ia Fig. 2. 



