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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



the same composition as that of Brunswick Square and Hove at 

 Brighton, previously described. At all the localities along the coast 

 which are flat and far removed from the chalk-hills, the chief mass 

 of the re-aggregated materials* have been derived from the Tertiary 

 formations, the harder parts of the latter now only remaining on the 

 sea-shore, as in the Bognor, Middleton, and Oar rocks ; or still form 

 partial cliffs as at Bracklesham. Wherever you examine this detritus, 

 whether it be on the external slope or talus of the chalk-hills, or in 

 the broad, slightly inclined flats extending to the sea, you find that, 

 whatever may have been the materials acted upon, they have all 

 been violently broken up, and gathered tumultuously and without a 

 symptom of having been subjected to ordinary tidal coast-action to 

 produce stratification, or long-continued aqueous abrasion to round 

 the flints ; nor do they anywhere contain marine remains, except where 

 the detritus has been shed off into the low situation, at Hove, and has 

 there encroached upon the sea-level. All this drift I consider to have 

 been shed off from north to south, and to have been formed coinci- 

 dently with the flint-drift described as lying between the escarpment of 

 the South Downs and the central dome of the Wealden. 



Round Tertiary Shingle on the South Downs. — The only decided 

 exception to the complete denudation of the tertiary rocks throughout 

 the slopes of the South Downs, with which I am acquainted, in addi- 

 tion to the well-known example at Newhaven, is a local accumulation 

 of rounded gravel (within the range of the chalk in situ) to which 

 my attention was directed by Sir H. Goring and Lord Edward Howard. 

 The chief mass is at Clapham Common, half a mile east of Patching, 

 and in the angle between the old Arundel and Brighton road and 

 that which traverses to Horsham. There it has been long quarried 

 for gravel, and is associated with much tenacious mottled clay, ex- 

 tensively used as brick-earth. On examination, it is evident that 

 this clay and gravel deposit, lying as it does about three miles inland, 

 at about 150 or 200 feet above the sea, and spread over a broad talus 

 in a depression of the chalk-hills, could not be considered in the light 

 of a raised beach, like that at Brighton, but must belong to an early 

 tertiary epoch ; in other words, to the pebble-beds of the Plastic-clay 

 (or Woolwich Beds). One or two layers of these rounded pebbles mark 

 a slightly undulating stratification in the clay ; but their overlying 

 portions have been since re-aggregated in heaps which cover the clay. 

 Not a single angular fragment of chalk or flint is mixed up with these 

 pebbles or with the clay, except those which may have fallen from 

 the thin coating of angular drift which overlies them. The deposit, 

 in short, is such as it was originally aggregated on the ancient surface 

 of the chalk when the tertiary beds were formed by sea and tidal 

 action. Although in my visit I detected no fossils in it, I have 

 no doubt, from the nature of the clay and sand and the form of the 

 pebbles (exclusively rounded chalk-flints), that it is truly a portion of 

 the Plastic-clay formation in situ, which has resisted denudation f. 



* The Drift at Bracklesham contains Elephant-molars. 



f Striking examples of this resistance to denudation are seen in the cappings 

 of the hills of chalk in Salisbury Plain; as at Sidbury Hill, Chiltern Clumps, 

 Quarley Mount, Thorney Down, and Clairbury, all of which consist of plastic-clay 

 and bighly rounded pebbles of chalk-flints. — [October 1851.] 



