﻿MURCHISON — FLINT DRIFT OF S.E. ENGLAND. 



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south of Alfriston, at which place large hlocks of tertiary grey -wether- 

 sandstone also occur as boulders. 



These heaps of detritus occupy low hills considerably above the 

 present drainage, and in their irregular distribution and unstratified 

 aspect resemble the drift of other districts alluded to. 



My notion therefore is, that when one portion of the Wealden 

 drift was swept along from west to east in a depression between 

 the South Downs and the elevations of the central dome, other 

 portions of the same were deposited in these gorges. 



In the example of the river Ouse, it is indeed probable that the 

 collection of drift to the south of the Lewes Castle Ridge was much 

 increased by the debris thrown into this recess by the operation of 

 the anticlinal elevation before alluded to. The position and relation 

 of this Lewes drift are much too remarkable not to be specially 

 noticed ; the more so, as it is owing to the railway cuttings that de- 

 tails have been laid open which were less perfectly seen when Dr. 

 Mantell gave so deep an interest to every feature around his native 

 town*. No transverse-flowing river, which escapes from the Weald 

 through the South Downs, passes through so narrow a gorge of the 

 Chalk as the Ouse at Lewes, the ancient castle being built upon a 

 promontory of that rock, which running from the main mass of the 

 formation on the west, advances to within a very short distance of 

 the hill called "Cliff," and where the abrupt face of the chalk so 

 clearly demonstrates that the gorge has been formed by a great 

 transverse rent. The face or side of that chalk promontory is too 

 abrupt to have permitted the accumulation of foreign drift in any 

 quantity, but the moment the observer has passed the gorge, he sees 

 a wide and flat alluvial ellipse, subtended on all sides by sloping 

 chalk-hills, which, separated in one part by a distance of nearly two 

 miles, approach closely again at Rodmill and Itford. Thence the 

 river once again flows in a gorge, much more open than that of 

 Lewes, and again the valley opens to some width between Newhaven 

 and Seaford. 



Now, the chief accumulations of drift occur precisely where one 

 might best expect to find them. First, in the recess in the chalk on 

 the right bank of the Ouse and immediately south of the Castle of 

 Lewes and the tunnel of the London railroad (see fig. 6). There, 



Fig. 6. — Diagram, showing the Position of the Angular Drift and 

 its overlying Argillaceous Loam in the Chalk-valley at Lewes. 



N. Lewes. Cliff. S. 



c x s c d 



X. Drift and Combe-rock (with Fossil Mammalia), covered by argillaceous loam. 

 s. Silt. c. Chalk (upper and lower). d. Chalk-marl (axis). 



the angular flint-drift has been cut into to a depth of from 12 to 15 

 feet, and is covered by a thick mass, as unstratified as itself, of 



* See The Fossils of the South Downs, or Illustrations of the Geology of Sus- 

 sex, by Gideon Mantell, F.L.S., G.S. &c. 4to. London, 1822. 



