470 PROCEEDINGS OF THE GEOLOGICAL SOCIETT. [June 3, 



in situ beneath the Glacial Clay, its occurrence here having been 

 brought before the Society as far back as 1835* by Mr. Spencer. 

 That gentleman, however, speaks of it only as composed of flint- 

 pebbles and sand ; and when I saw the bed exposed, a few years 

 back, during the progress of the railway works, it appeared to me 

 almost wholly made up of sand and flint-pebbles, the quartz and 

 quartzite fragments being unfrequent. The same constitution ap- 

 pears to me also to mark the bed as it occurs in the patches over the 

 London-Clay summits before described, as, e.g. at Bamet, Totteridge, 

 Hadley, &c. In the south-easterly direction from the district de- 

 scribed by Mr. Hughes, this pebble-gravel is far less frequent, and 

 its position there does not indicate its having once spread over a 

 continuous plain ; but it presents itseK occasionally beneath the 

 Glacial Clay, between the elevated outliers of the Bagshot Sand, 

 around which the Glacial Clay has been bedded, as is shown in the 

 accompanying section, at They don Mount and Stapleford Tawney ; 

 and it is here again almost exclusively composed of pebbles derived 

 from the pebble-beds first described and marked 4 in the section, 

 partly unbroken, and partly broken into fragments of various sizes, 

 fragments both of quartz and quartzite being rare. In neither of 

 the directions, therefore, in which these " higher plain gravels " are 

 to be traced southward from the area described by Mr. Hughes do 

 we find that large admixture of quartz in them which he considers 

 to prevail over the area embraced in his paper. Moreover both the 

 quartz and quartzite-pebbles are extremely abundant in the Middle 

 Glacial Gravel, where that formation comes out from beneath the 

 Glacial Clay further to the east, at Writtle near Chelmsford. 



The Gravel which caps Shooters Hill in Kent, if it be not of Post- 

 Glacial age, may probably belong to the bed No. 6. 



The view taken by Mr. Hughes, that this pebble-gravel belongs to 

 a period anterior to the gravel of the lower plain, is of more general 

 importance than at first sight appears, since, according to my view 

 of the distinction of the beds, it involves the admission that there 

 has been a period intermediate between that of the pebble-beds 

 marked 4 in the section and the Glacial, during which the sea occu- 

 pied these counties, and deposited the Gravels of the Higher Plain. 

 That view seems based principally upon the composition of the 

 gravel in question where it occurs in Herts ; but when its composi- 

 tion further south and south-east is considered, with its position 

 relatively to the pebble -beds Xo. 4 capping the Bagshot outliers, its 

 age appears to me to be intermediate between the Middle Glacial 

 Gravel (No. 5) and the Glacial Clay that overlies the tAvo gravels 

 alike, its accumulation in these parts having been due to the 

 destruction of the pebble-beds marked 4, which formed the shore 

 during the interval which elapsed between the setting in of the sub- 

 mergence which closed the Middle Glacial formation and the disap- 

 pearance of the highest elevations, crowned with bed No. 4, be- 

 neath the sea of the Upper Glacial Clay. 



It may be fairly objected, as was done upon the reading of this 

 * Proceedings, vol. ii. p. 181. 



