ESSAYS 317 



rivers do) towards the periphery. In such a long process all traces of the topmost 

 strata may well have vanished, and in some of our dissected gravel-capped 

 plateaux (e.g. near Farnham) we have proofs of how quickly the materials of such 

 gravels often disappear. But in fact flints are sometimes found at great distances 

 from the escarpment, having been reported from Horsham, 1 on the very axis of 

 the anticline ; and while such rare occurrences are quite in keeping with either 

 of the older hypotheses, they appear to me absolutely fatal to Major Marriott's. 



(3) " The presence of chert and ragstone, and ferruginous sandstone 

 peculiar to the Lower Greensand spread over parts of the highest of the chalk 

 plateaus." And we are told on p. 598 that " the significance of this appears to 

 have escaped notice." Now, if there had been a Wealden Island (which we have 

 seen to be out of the question) in Cretaceous times, there should have been 

 chert, etc., in the Chalk itself ; and even on the assumption of a submerged bank 

 of Lower Greensand and other strata, it is strange indeed that the lower Eocene 

 beds, which abound in rolled chalk flints, contain no chert. As most of these 

 fragments were admittedly (p. 601) deposited in Pliocene times, all that they 

 really prove is that the existing drainage system was not yet fully established, 2 and 

 this has been adduced as evidence in favour of planation. 3 



(4) " The perfectly simple history of the ' transverse ' valleys on this assumption. 

 The explanation of these valleys is avowedly a great difficulty with all other 

 theories." It would be interesting to learn where this "avowal" is to be found, 

 and where these valleys are " so often quoted as presenting a geological difficulty " 

 (p. 602). The general principles governing the formation of such valleys, as laid 

 down more than half a century ago by Greenwood, Jukes, and others, have for 

 many years been accepted all over the world ; and, although here and there a 

 dissentient voice may be raised (Mr. F. R. Bennett is quoted as not fully satisfied), 

 I am not aware that any one has definitely formulated any objections. And when 

 we consider the matter more closely, is there really any physical (as distinct from 

 geological) difference in the starting-points offered by Major Marriott's theory and 

 that of planation? In both of them the valleys originate on the central (Hastings) 

 beds, and when the Chalk emerges it is the thin edge of the wedge which first 

 appears, and across this the transverse streams prolong their courses without 

 opposition. The subsequent deepening of these valleys and concomitant excavation 

 of the longitudinal ones also appears to me to be the same in both cases. I gather, 

 however, that Major Marriott sees a " crucial " difference between the two, and he 

 speaks of the streams descending from the higher ground "making frontal attacks 

 on the chalk and spreading east and west until they found suitable exits" (p. 593). 

 That is a process which I do not profess to understand, but it does not appear to 

 account for the initial stages of the escarpments. 



The whole question of these valleys is closely bound up with that of the escarp- 

 ments, and here again it is necessary to remember that the Weald is not really 

 unique, and that there are many other examples of chalk hills being cut through 

 by transverse rivers. On the one hand we have large rivers like the Thames at 

 Goring, and the Dorset Stour near Blandford, which probably originated on 

 coastal plains closely comparable to the hypothetical marine plain of the Weald ; 

 and on the other we see the tiny inliers of Ham and Kingsclere, where the streams 



1 Topley, op. cit. p. 200. 



2 See Bonney, The Work of Rain and Rivers (Camb. Manuals of Science), 

 p. 106. 



3 Quart. Journ. Geol. Soc. vol. Ixvi. 1910, pp. 648 et seq. 



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