62 hk. M. Deeley—The Thames Valley Gravels. 
which may be connected with fluvio-glacial fans which came from 
the Leighton Buzzard and Dunstable Lobes, for they both contain 
pebbles of the Northern Drift. Patches of gravel at about the same 
height also occur in the neighbourhood of Oxford, ete. The drift 
deposits in the north-western portion of the Map, Fig. 1, have not 
been surveyed in detail, but enough is known to show that large 
fans of fluvio-glacial gravel from the Buckingham Lobe occur there. 
Owing to the fragmentary nature of the drift deposits in the Oxford 
Basin, and the fact that some areas have not been mapped in detail, 
the probable distribution of the fluvio-glacial deposits of this district 
have been drawn in dotted lines. The evidence furnished by these 
much disturbed and denuded high-level gravels is to the effect that 
when the Chalky Boulder-clay ice poured its debris into the Oxford 
Basin of the Thames Valley, portions of the basin had been denuded 
so as to form an extensive flat area which now stands about 300 feet 
above the sea. Over this area the fluvio-glacial gravels were spread 
in a great sheet covering such of the old river gravels as remained, 
and also the surrounding low country. The floor upon which the 
gravel rests is now wonderfully level, the slope towards the outlet 
of the Oxford Basin at Goring being quite small. The 300 feet 
fluvio-glacial gravels of the Oxford Basin may have been fifty feet 
thick, as they are further down the river; but mere fragments of 
them remain. 
When a terrace is spoken of as being the 300 foot terrace it must 
be understood that the gravel and sand rest upon a platform of older 
rocks whose upper surface is at a height of 300 feet above O.D. 
During the Chalky Boulder-clay period there must have been a 
very large stream of water flowing through the Goring Gap, a stream 
which partially dried up in the winter months. With this stream 
came Bunter pebbles into the London Basin, thus accounting for 
their presence to the west of points where they also reached the area 
from the St. Albans Ice Lobe. 
On Fig. 2 the heights above the sea and thicknesses of a number of 
these outliers of gravel inthe London Basin are plotted. The fluvio- 
glacial and other old gravels of this area, although the district has 
suffered much denudation, are less fragmentary in character than in 
the Oxford Basin. Indeed, they cover very considerable areas and 
their arrangement is much more easily traced. 
In Fig. 2 the dotted line BB shows the average height of the bed 
upon which the ‘schotter’ formed by the ‘ braided streams’ rested, 
whilst the line C C shows its upper limit. These levels must only be 
regarded as approximately correct. The gravel beds must have varied 
very considerably in thickness, often finishing off as a feather edge 
on the slopes of the valley sides. The gravel and sand patches which 
have been used to draw these lines are shown on the section, being 
named after some small town, village, or hill. The heights have been 
ascertained as closely as possible either from Ordnance Survey 
contoured maps or from the Drift coloured maps of the Geological 
Survey. 
In the Thames Valley, east of Goring, and generally capping the 
higher Tertiary hills, there are deposits which Whitaker has called 
