Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/123

 Figure 1.-The Aspect presented by the Gravel Brows of the Thames and Hampshire Areas towards the Chalk Country.

1. The Chalk. 2. The Thanet and Woolwich beds. 3. London Clay. 4. Lower Bagshot. 5. The Bracklesham Beds. a, a. The respective Gravels of the Thames and of the Hampshire sheets.

in relation to the chalk country that separates them may be more readily apparent.

Further, Mr. Codrington shows that these gravels cap, in the form of outliers at an altitude of 400 feet, the chalk ridge stretching from east to west through the Isle of Wight, the elevation of which, like that of the Hog's Back and of Portsdown Hill, followed, as I contend, the Thames gravel, and was coeval in its formation with the upcast of the chalk over the south of England. The double section (page 26) will make more intelligible the views which I hold of the relation of the two gravel- areas to each other, its direction being indicated by a line on Maps II. and III.

The upper representation shows the condition of the Chalk and Tertiaries after the Glacial period, and the removal. by denudation of the glacial beds, whose brow of denudation occupies the northern side of the Thames at elevations reaching to upwards of 300 feet. The removal of the Tertiaries and Chalk had been partially effected by this same denudation, but mainly effected by that preglacial denudation associated with the curvilinear configuration to which, in the footnote at pages 21 and 22, allusion has been made.

This upper representation is that of the state of land and water in Map II., while the lower shows the same after the upthrow in which the rectilinear ridges of Portsdown Hill, the Guildford Hog's Back, and of the isles of Purbeck and "Wight originated. By this upward movement the chalk country was converted into land, the sea confined within the Weald on the one side, and Mr. Codrington's inlet established on the other ; while the part of the