1XXX PKOCEEDINGS OE THE GEOLOGICAL SOCIETY. [vol. lxXV, 



the site of the old Sub-Wealden Boring and Avithin a mile or two of 

 the more recent Battle Boring, and the combined results of the two 

 give positive evidence as far down as the Oxford Clay. After 

 passing these borings the section-line is bent 20° more to the west, 

 in order to catch the landward outcrop of the Upper Cretaceous 

 rocks near Beachy Head. I have not ventured to prolong the 

 hypothetical position of the Palaeozoic floor beyond the northern 

 part of the section ; but the diagram, as it stands, brings out quite 

 clearly the lenticular outline of the aggregated Mesozoic formations, 

 and shows the essentially superficial character of the famous 

 Wealden anticline. 



With this section in view, we will resume for a moment the 

 consideration of Topley's idea that the Wealden dome may have 

 been an original dome of sedimentation. 



The differential accumulation of Mesozoic deposits in the basin 

 having proved to be so much greater than Topley was aware of, it 

 might seem that his case was thereby strengthened. But, as I 

 have pointed out in a previous publication, 1 there are, among the 

 infilling sediments, at several horizons, deposits which possess cha- 

 racters denoting shallow water and approximate equality of depth 

 over the whole area during their accumulation : as, for example, the 

 Corallian Limestone ; the estuarine band of the Purbeck ; the 

 estuarine top of the Weald Clay ; the muddy sandstones of the 

 Kellaways and Portland Beds ; and the coarser sands of the Lower 

 Greensand. The present position of these originally horizontal 

 planes, and their relationship to each other, afford positive indica- 

 tion that the lenticle of sediments was accumulated in a subsiding 

 basin, and was not piled up as a dome. The horizon-planes are not 

 parallel, but, when drawn in section, are seen to radiate slightly, like 

 the ribs of a partly-opened fan, with their widest expansion towards 

 the middle of the Weald (as illustrated in fig. 1, p. lxxvi, in which 

 some of these planes are denoted by thick lines). 



We learn from them that, from early Triassic to mid- Cretaceous 

 times, besides the general movements of elevation and depression 

 affecting the whole region, there was a persistent local sagging or 

 downward movement of the Palaeozoic floor under the middle of the 

 Weald, with relative stability or even sometimes uprise at the 

 flank. Each originally horizontal plane in turn underwent this 

 local tilting, and the effect was, of course, cumulative upon the 



1 ' On the Mesozoic Rocks, &c.' op. supra cit. Chapter vii, p. 88. 



