220 Mr. G. J. Hinde’s Notes on the 
buildings or removed for the repair of roads, it has seemed to me 
opportune to bring before the Club some notes on their characters. 
The history and origin of these gravels are so closely connected 
with the formation of the valleys and the geological nature of 
the country in the drainage area of the Wandle basin, that a 
short preliminary sketch of the geology and present physical 
configuration of the district is necessary to understand them. 
The southern boundary of the present drainage area of the 
Wandle is the well-known escarpment of the Chalk overlooking 
the east and west valley in which Oxted, Godstone, and Merst- 
ham are situated. To the east it begins on the high ground of 
Botley Hill, near Woldingham, and follows the general summit 
of the escarpment westwards to near Walton Heath, a distance 
of about eleven miles. The eastern line of the watershed extends 
from Botley Hill to the north-west in the same general direction 
as the high road over Worms Heath and through Warlingham 
to Sanderstead, but soniewhat to the west of the road itself. 
From Sanderstead the line continues to the Addington Hills, 
Shirley, and more to the north along the ridge of Upper Nor- 
wood, and thence through Streatham and Upper Tooting to the 
Thames. On the west side, the line of watershed passes over 
the high ground of Walton Heath in a north-easterly direction, 
near to Walton-on-the-Hill, Banstead Newton, and Burgh Heath, 
then more easterly to near Banstead and Woodmansterne, and 
the west side of the valley of the Wandle at Carshalton, and 
northerly through Morden and Wimbledon to the Thames. 
As the result of the convergence northwards of the east and 
west lines of watershed, the Wandle basin, just to the south of 
Croydon, is not more than about five miles in width, or less than 
half that of its southern border. A line drawn through the 
south end of Croydon roughly divides the drainage area of the 
Wandle into a southern portion, mainly underlaid by chalk, and 
a northern, underlaid by Lower Tertiary beds and London Clay. 
In the southern portion the Upper Chalk forms a plateau-like 
surface, elevated from 600-868 ft. above Ordnance datum * on 
the southern margin of the escarpment, and gradually sloping 
northwards to levels of 500-550 ft. above Ordnance datum at 
Banstead, Coulsdon, and Sanderstead. At Riddlesdown the 
plateau is 400 ft., and at the Russell Hill, on the opposite side 
_of the valley, 362 ft. Nearer Croydon, owing to the northerly 
dip of the chalk, the levels are still lower, and at South Croydon 
the chalk disappears below the surface, and is replaced to the 
north by Tertiary beds. 
This comparatively high sloping plateau is not entirely of 
* The elevations given in this paper are taken from the 6-inch maps of 
the Ordnance Survey, 
