286 WEALD, HOW DENUDED. [Ch. XIX. 



of some beds of gravel, loam, or drift in the southeast of England, to im- 

 agine important dislocations of the chalk and local changes of level since 

 the Glacial period, such speculations are in harmony with conclusions 

 derived from independent sources, or drawn from the exploration of for- 

 eign countries. 



It was long ago observed by Dr. Mantell that no vestige of the chalk 

 and its flints has been seen on the central ridge of the Weald or on the 

 Hastings Sands, but merely gravel and loam derived from the rocks im- 

 mediately subjacent. This distribution of alluvium, and especially the 

 absence of chalk detritus in the central district, agrees well with the 

 theory of denudation before set forth ; for, to return to fig. 321 (p. 273), 

 if the chalk (No. 2) were once continuous and covered everywhere with 

 flint-gravel, this superficial covering would be the first to be carried away 

 from the highest part of the dome long before any of the gault (No. 3) 

 was laid bare. Now, if some ruins of the chalk remain at first on the 

 gault, these would be, in a great degree, cleared away before any part of 

 the lower greensand (No. 4) is denuded. Thus in proportion to the 

 number and thickness of the groups removed in succession, is the prob- 

 ability lessened of our finding any remnants of the highest group strewed 

 over the bared surface of the lowest. 



But it is objected, that, had the sea at one or several periods been the 

 agent of denudation, we should have found ancient sea-beaches at the 

 foot of the escarpments, and other signs of oceanic erosion. As a gen- 

 eral rule, the wreck of the white chalk and its flints can only be traced 

 to slight distances from the escarpments of the North and South Downs. 

 Some exceptions occur, one of which was first pointed out to me in 1830, 

 by the late Dr. Mantell. In this case the flints are seen near Barcombe, 

 three miles from the nearest chalk, as indicated in the annexed section 

 (fig. 331). Even here it will be seen that the gravel reaches no farther 



^-^* Fig. SSL 



Section from the north escarpment of the South Downs to Barcombe. 



A. Layer of unrounded chalk-flints. 



1. Gravel composed of partially rounded chalk-flints. 



2. Chalk with and without flints. 



3. Lowest chalk or chalk-marl (upper greensand wanting). 



4. Gault 5. Lower greensand. 6. Weald clay. 



than the Weald clay. But it is worthy of remark, that such depressions 

 as that between Barcombe and Offham in this section, arising from the 

 facility with which the argillaceous gault (No. 4, map p. 272) has been 

 removed by water, are usually free from superficial detritus, although such 

 valleys, situated at the foot of escarpments, where there has been much 

 waste, might have been supposed to be the natural receptacles of the 

 wreck of the undermined cliffs. The question is therefore often put, how 



