408 Rev. Dr. Irving — Elevation of the Weald. 



feet above the sea, while the Miocene strata lie horizontally against 

 the highly inclined older strata on the north side), 1 changes which 

 effectually mark off the Older from the Younger Tertiaries of Europe. 



A gradual subsidence during Pliocene time of the Tamisian area 

 would admit of the extension of the northern waters again to the 

 west, so as to cover a portion of the East Anglian area, and give us 

 the Crag deposits in a shallow sea bounded on the west and south 

 by a zone of older Tertiaries, across which there must have been 

 extensive transport of detritus from the elevated Cretaceous regions 

 of East Mercian England on the north-western side, and the Weald 

 on the southern side. These seem to me to have been approximately 

 the physiographic condition under which the plateau-gravels north 

 of the Thames were accumulated. And if this were so, there is no 

 real necessity for associating the Westleton Shingle of Prestwich 

 with the plateau-gravels on the south of the Thames ; for the flint 

 pebbles and fragments of the former were in all probability derived 

 from the Chalk of Norfolk and Suffolk. 2 The list of organic remains 

 of the Westleton and Mundesley Beds, given by Prof. Prestwich 

 in Part I. of his recent paper, shows such a preponderance of land- 

 and fresh- water-remains as to suggest an estuarine origin for these 

 beds ; so that we might not be very far wrong if we regarded them 

 as accumulated at the beginning of the Quaternary period near the 

 western margin of the older Rhine estuary, which received the 

 drainage of the East Anglian and lower Tamisian areas. 



The admission that the inland representatives of the Westleton 

 and Mundesley shingle-beds may be of terrestrial origin, similar 

 to that which is assigned to the plateau-gravels on the south side of 

 the Thames, would remove two difficulties, which must. I think, 

 have presented themselves to the minds of others besides myself: — 



(1) It is difficult to accept the view of such a wide-spread marine 

 floor at about the beginning of the Quaternary period, as would 

 extend the waters of the German Ocean to the flanks of the 

 Cotswolds, with a subsequent elevation towards the west of some 

 500 feet, unless independent and collateral evidence of a less 

 equivocal nature can be adduced in support of the hypothesis. 



(2) There is a great difficulty in explaining the unfossiliferous 

 character of those inland gravels, on the theory of ' decalcification ' ; 

 since so many of them are covered (as shown in Prof. Prestwich's 

 sections 4 ) by Boulder-clay, which must have served as an impervious 

 protection to them from the action of atmospheric carbonated waters. 

 ]t is somewhat curious that this theory of decalcification has been 

 applied where it will not very well work, but not to the plateau- 

 gravels of the Southern Drift, where the same difficulty does not arise. 



The recognition of the Pliocene age of those inland gravels and sands, 

 and of their terrestrial origin, would give us also a wide limit of 

 time for the formation of the East Mercian Chalk Escarpment, and 

 of the present valley-system, and so remove a still further difficulty. 



1 Credner, op. cit. p. 722. 



2 The inference fairly to be drawn from the absence of Tertiary deposits in the 

 Midland and Northern Counties is in accordance with this view. 



3 See Q.J.G.S. vol. xlvi. pp. 115-117. 4 Q.J.G.S. loc. cit. 



