Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/107

 gence and denudation. The Glacial beds of East Anglia have undergone a similar emergence and denudation ; and even those who attribute the Wealden denudation to atmospheric and fluviatile agencies admit that the Lower Tertiaries and Chalk over the south of England underwent a previous denudation or planing off by marine agency ; but where are the beds with marine fossils in East Anglia or over the south of England representing such emergence and denudation? These questions might be extended to the denudation of the coal-measures and other old rocks ; but the phenomena presented by denuded areas appear to me to show, uniformly, that a denudation effected during upheaval* is unrepresented by beds with contemporaneous marine fossils deposited over the denuded area. Upon any introduction afterwards of the sea, however, we get these beds — as, for instance, the Kelsea gravel in Yorkshire, the fen-gravels of East Anglia, and the brick-earth of the War in Norfolk : but there has been no such reintroduction of the sea into the Weald since its denudation, unless it be in the Lewes levels. The beds with marine fossils contemporaneous with the Wealden denudation are to be looked for without the Weald, i. e. beyond the region of upheaval and denudation ; and thus it is, as well as for the other reasons assigned in the sequel, that I refer the fossiliferous mud-bed of Selsea, lying in the depressed and undenuded fold between the two areas of upheaval and denudation, the Isle of Wight and the Weald, to the period of that upheaval and denudation.

In the accompanying map, by means of shading in the escarpment carefully reduced from the ordnance map, the very conspicuous features of mouths opening towards the Weald, presented by the gorges in the chalk escarpment between Guildford and Dover, and by that in the Lower-Greensand escarpment at Yalding, are made apparent†. The gorges of the South Downs present no such feature.

Now patches of gravel containing Tertiary pebbles occur near one or other of these mouths : and it is clear that streams flowing from the north through the Tertiary and Chalk area, and debouching through these mouths into a sea occupying the area within these escarpments, would necessarily bring an abundance, both of angular chalk-flint and of Lower-Tertiary pebbles into the Weald, there to intermingle with fragments having their parentage within the Weald itself.

My proposition is that the violent disturbances from east to west at some time subsequent to the older Tertiaries to which, it is universally admitted, the Weald owes its present form‡ took place

and then deposits its sediment with contemporaneous marine organisms — preceding this usually, however, with beds of rolled fragments.
 * It is the reverse with denudation during depression ; for there the advancing sea, as e. g. that of the Lower Tertiaries over the Chalk, planes off its floor

† To show better the physical features of the scarp, the strip of Atherfield clay that forms the foot of the Lower-Greensand escarpment has been shaded in with the Weald clay, instead of, as is usual for geological grouping, with the Lower Greensand.

‡ In order not to encumber the case discussed in the body of the paper, I have