60 R. M. Deeley—The Thames Valley Gravels. 
passed. Whether the Leighton Buzzard and Dunstable lobes ever 
coalesced and passed down the valley towards Aylesbury is uncertain. 
If they did they may have sent floods down some of the gaps in the 
Chilterns as well as down the Thame Valley. 
D. St. Albans Lobe. South of St. Albans there is a large patch 
of boulder-clay which shows that the ice passed through the gap 
between Hatfield and St. Albans. The gap has a height of about 
250 feet. From the ice which passed through it a great amount of 
debris was thrown into the Thames Valley down the Colne River, 
in the valley of which there are wide spreads of gravel, some of the 
terraces of which are portions of the fluvio-glacial fan formed by 
the water liberated from the front of the Chalky Boulder-clay 
ice-sheet. 
EK. Brent Lobe. The gravels of Dollis Hill and Hendon show 
that an ice-flow from the north-east passed through a gap north of 
Hampstead and Highgate into the Brent Valley. - 
F. Lea Valley Lobe. The main ice invasion of the district covered 
by the Map, Fig. 1, came down the Lea and Roding Valleys and 
pushed its front into the then forming fluvio-glacial gravels of the 
Thames; for at Hornchurch the boulder-clay of this lobe has been 
found resting below the gravel. It must be remembered that the 
gravels we are considering and the Chalky Boulder-clay are con- 
temporaneous deposits. 
G. Crouch Valley Lobe. A considerable volume of ice mounted 
the watershed between the Chelmer and the Crouch. Some patches 
of sand and gravel in the Crouch Valley render it somewhat likely 
that this valley was occupied by a fluvio-glacial fan which ran in an 
easterly direction to the Thames Valley. 
H. Malden Lobe. A lobe of ice passed towards the east, south 
of Tiptree Heath, and sent out a fluvio-glacial fan towards the 
north-east. 
Other ice lobes moved towards the east down the valleys of the 
Suffolk rivers, but how far north the Thames then ran before reaching 
the sea is unknown at present. 
The arrows over the northern portion of the map show the probable 
direction of the ice-flow. Harmer’ has already given the probable 
directions of the flow of the ice from the north over the Fenland as 
far south as Royston. The directions of the ice-flow of the area we 
are dealing with, as shown on the Map, Fig. 1, are in entire agree- 
ment with his views concerning the movement of the more northerly 
portions of the ice. The coarsely hatched area, the greater portion of 
which follows the course of the Thames River, is the probable area 
occupied by the Tilehurst fluvio-glacial gravels of the main river when 
the ice reached its most southerly limits. Along the valley a dotted 
line has been drawn, and Fig. 2 is a section along this line. The 
present upper surface of the Thames alluvium is shown by the line 
AA. The slope amounts to about 2°5 feet per mile. 
The terraces and patches of gravel we have to make use of to 
ascertain the levels and thicknesses of the fluvio-glacial gravels of the 
old Thames River are not very numerous, and are no doubt mere 
1 Jubilee Volume of the Geologists’ Association, vol. i, p. 108. 
