Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/114

 3rd. The difficulty of reconciling the presence of Tertiary pebbles in certain Wealden gravels with an origin by means of rivers flowing in the direction of the present ones, however high we imagine those rivers to have been.

4th. The antagonism between the character and form of the major valley of the Weald and that of any conceivable excavation which could result from the agency of rivers, not merely from rivers coincident with the present ones in direction, but from any rivers at all.

5th. The proof which the position of the gravels of the Thames, of East Essex, and of the Canterbury heights, and especially the position of the lofty ridge dividing the Thames and East-Essex gravels from each other, furnishes that the sea of this gravel-period was to the south of these gravel-sheets.

6th. The circumstance that the old coast-contour, when the sea lay within the Weald, and the channels and river-drainage entered it from the north, remains now stamped, as from a die, on the Chalk and Lower-Greensand escarpments, except in the particular region where that on the chalk was obliterated by the excessive marine denudation consequent upon the acute upthrow of the Guildford Hogsback — especially the dry inlet mouth at Merstham.

7th. The natural manner in which the gravels with Tertiary pebbles, mentioned in proposition no. 3, fall into their places, if they be regarded as having received these pebbles by means of channels and rivers from the north ; and the sufficient explanation which a tidal indraught from the south, when the shore-line was chalk, and the principal denudation of the subcretaceous strata not yet accomplished, offers for the small quantity of subcretaceous material and enormous quantity of flint possessed by the Thames, East-Essex, and Canterbury-heights gravels.

8th. The existence of a cause, in the shape of an isthmus at Dover, which was adequate to induce a tidal scour sufficient, with the river-flow from the north, to produce a denudation of the form and character which the major valley and the minor valleys together present ; the equally adequate cause for a cessation of this denudation, and for the mastery so attained by the elevatory action over the denudation, which the opening of the Dover Straits (generally admitted to be of a late Postglacial date) furnishes ; also the general fitting in of all these propositions with one another, and with the features presented, on the one hand, by the very recent opening of the mouths of the Thames and Crouch through the great ridge, and the absence from the valleys of the Thames mouth and of the Crouch river of either gravel or brickearth ; and, on the other hand, by the character of the Selsey deposits.

Note explanatory of the Map (PI. I.).

In order that the physical features may appear, the Atherfield- clay has been shaded in with the Weald-clay, instead of, as usually, with the Lower Greensand.

The lines A and B indicate those of the two sections, A and B, which