1867.] WOOD SOriH-EAST OF EXGLAXD. 401 



Survey-sheet, No. 1, by comprising parts of four out of the eight 

 conspicuous arcs of the series, affords the means of minutely testing. 

 The outermost (and consequently the largest), extending from Bath 

 to Stamford, and taking in the western scarp of the Cotteswolds, only 

 cuts through the Glacial beds near Market Harborough, the structure 

 and delineation on the map of the Glacial beds south and west of that 

 place showing theii' denudation in this direcrion. Those arcs which 

 cut through the Glacial beds in Essex, and of which the large Suiwey- 

 map affords easy means of testing, embrace the cross valleys indenting 

 the northern scarp of the Weald, such as those through which the 

 lledway and Darent flow in part of their courses, being the dii^ection 

 in which fig. 4 shows the denudation to increase from the lip of 

 the Glacial beds in this part. It would be useless to attempt to de- 

 scribe these arcs further, as their delineation on the map must be seen 

 and studied for their importance to be realized ; but their structure, 

 wherever they cut thi^ough the Glacial beds, shows them to have 

 formed troughs occupied by arms of the Postglacial sea, which has 

 deepened them by denudation. The general grouping of the Glacial 

 beds in relation to them, and the south-westerly increment of denu- 

 dation which those beds display, indicate, as it appears to me, that 

 the progressive scarjDing of the arcs in this direction has been due 

 to the prolongation of the denudation there. 



Several sections, in illustration of the structiu-e of these arcs in 

 various parts, will be found in the memoir ; but I will only trespass 

 upon the Society with three — two of them illustrating the structure, 

 in different parts, of the outermost arc but one of the Kentish series, 

 which I select as being the most suitable to show the part played by 

 denudation in their creation, and the third illustrating the structure 

 of a part of one of the innermost arcs of the series (being one that 

 traverses the surveyed Ordnance sheets accompanying the memoir). 



Fig. 7, which intersects the outeiTQOst but one of the Kentish 

 series of arcs, does so at a part where the trough of denudation giving 

 rise to the arc enters the body of the chalk, disconnecting itself from 

 the outcrop of the Gault. It is evident that in this part, which is as 

 well defined as any part of the arc, the structure giving rise to the 

 arc-crest is one of denudation, and not in any way due to the out- 

 crop of the base of the chalk; and it is equally evident that the 

 scarp of the chalk which occiu's above Eoyston is not due to at- 

 mospheric denudation, but to the erosion of a trough several miles 

 wide, which is cut down on both sides from the Chalk and Upper 

 Glacial clay into the Gault. 



Fig. 8, on the other hand, exhibits the arc formed by the scarp 

 of the chalk where no portion of that formation extends to the 

 opposite side of the trough. Although the general lie of the beds 

 seems antagonistic to an assumption that the elevation of the arc- 

 crest is due to the Postglacial disturbances yet it is evident that 

 there has been in this part an excessive denudation, first over the 

 crest of the arc, and subsequently in the trough, which latter denu- 

 dation has excavated the great vale of Aylesbury. Probably at the 

 incidence of the Upper Glacial clay by general submergence the 



