and on the Drift of the Eastern Counties. 197 



series* cap Galleywood Common, the valleyof the Chelmer having 

 been cut through the line of contact. The same feature may be 

 perceived all along this line between Badow and Writtle ; and in 

 Section C (PI. XVII.), I have shown the original position of the 

 beds of the lower Drift at their southern extremity, and the mode 

 in which the valleys have been cut through the district. Consider- 

 able alterations of the relative levels have taken place here, as 

 over all the rest of East Anglia, by the formation of the valley- 

 system, so that the Danbury outlier is forced up far above the 

 corresponding level of the old shore of the bay which may be 

 represented by Galleywood, now much below the level of the 

 lower Drift of Danbury. The section, however, is drawn with- 

 out reference to any of these changes of level, in order that the 

 position originally occupied by the lower-Drift beds may be 

 better shown. 



It is thus very obvious how the bay depositing this lower Drift 

 advanced inland by erosion as much as or more than by depres- 

 sion. Several examples of this advance by erosion occur. A 

 very interesting one is afforded by the section on the summit of 

 the Chalk inlier forced np at Claydon in Suffolk (see the 

 sketch below the map) : this section marks a stage when the bay 

 had advanced but a short distance inland from the Red-Crag 

 bay. Another example is afforded by the well-sinking at 

 Hasketon, near Woodbridge. The base of the London Clay is 

 brought up at Kyson, and the clay at that place has a thick- 

 ness of only some 50 feet between its base and the overlying 

 Crag ; but at Hasketon a well-sinking for 120 feet failed to 

 pierce the London Clay, and was abandoned, while at a short 

 distance on one side of this sinking, at a few feet higher level, 

 the lower Drift was pierced for 60 feet; and on the other 

 side of the London-Clay boring, both upper and lower Drift 

 have been pierced for the usual thickness of the district. More- 

 over, on a third side, the upper pr Clay Drift rests on this . 

 London Clay, and the valley has been cut through both 



* In the Sections attached to the paper of Mr. Prestwich on the corre- 

 lation of the English and Belgian lower tertiaries (Quart. Journ. Geol. 

 Soc. vol. xi. p. 241), the middle and part of the lower Bagshot are repre- 

 sented as denuded from Langdon Hill. Whether the Essex beds represent 

 the middle as well as the lower Bagshot, or the lower only, they at any rate 

 are nearly complete on Langdon Hill. The Essex Bagshot consists of 

 about 30 feet of sand and 20 feet of pebble-beds overlying the sand, and 

 on these pebble-beds the boulder-clay, where not denuded, rests. It is the 

 nearly complete preservation of these uppermost pebble-beds, on the 

 various outliers where the Drift clay has been denuded, that shows that 

 the lower Drift never extended over them ; the Bagshot pebble-beds may 

 be traced complete along the outliers until they pass under the Drift clay. 

 Nothing of the Bagshot scries, beyond this sand and overlying pebble-bed, 

 was ever deposited in Essex. 



