1870.] 



WOOD WEALD-VALLET DENUDATIOIf. 



25 



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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 sec- 

 tion (page 26) will make more in- 

 telligible 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 ef- 

 fected by this same denudation, 

 but mainly effected by that pre- 

 glacial 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 



