WESTLETON BEDS TO THOSE OF NORFOLK, ETC. 149 



to a depth of about 160 feet, and a width of from 2 to 4 miles, when 

 the newly made channel received its covering of Northern Drift 

 (2, fig. 13). 



The successive increments of depth *, acquired during the different 

 periods, are exhibited in the following section (see also fig. 12). 



Pig. 13. — Diagram-section across the Gorge of the Thames through 

 the Escarpment of the Chalk at Goring. 



1. Post-Glacial Drift. | 4, Lower Tertiary strata. 



2. Glacial Drift. j 5. Chalk. 



3. Westleton Shingle. j 



feet. 



A. Denudation during the early Glacial Pei'iod about 160 



B. Denudation during the later Glacial Period „ 220 



0. Denudation during the Post-Glacial Period „ 70 



Taking the height above the sea-level of the Westleton Beds here 

 at 600 feet, and that of the river at Goring at 150 feet, the 

 above figui'es give, but very approximately, the depth to which the 

 denudation of the valley at this place was carried during the succes- 

 sive Glacial and Post-Glacial epochs. 



The relative depths of B and C may be subject to considerable 

 correction. In the absence of sufiicient evidence at Goring, I have 

 been guided by the height of the high-level river-gravels at Oxford 

 and Eeading, where they are better developed. 



These measures, of course, vary at different places. Lower down 

 the Thames Valley, the channel A above Henley-on-Thames 

 (Bowsey hill giving the Westleton level) is above 200 feet deep, 

 while B is reduced in proportion. 



In the valley of the Lea, at Ware (fig. 14), taking the level 

 of the Westleton Shingle at Hertford Heath on the south at 316 

 feet, and at Sacombe Green on the north at 362 feet, and that of 

 the Lea at 110 feet, A and B together seem to amount, in round 

 numbers, to about 200 feet, whilst C does not seem to exceed 50 feet. 



In the valley of the lloding the level of the Boulder-clay is 

 about 100 feet below that of the Westleton Shingle, at Jack's Hill, 

 near Epping, whilst the extent of C is probably less than 30 feet. 



Other instances might be mentioned, but these will suffice to 

 show some of the stages in the denudation of this area and the 

 initial step in the formation of its river-valleys. It will appear, 

 from these facts, that the main denudation of the district has been 

 effected after Pliocene times, and that the first stage (A) in the 

 formation of the present gorge at Goring dates back to the time of 



* These hold whatever may be the age of the shingle. 



