116 R. M. Deeley—The Thames Valley Gravels. 
Lincolnshire. Buckland, many years before, had recognized this 
red chalk. Another lobe of the Chalky Boulder-clay glacier 
moved up the Ouse Valley and reached the limits shown in the Map, 
Fig. lL. 
If the above reading of the teaching of the boulder-clays, sands, and 
gravels be correct, then the first erratics to reach the Thames Basin 
were brought into the district by the British ice-sheet which reached 
the more northern and western portions of the Thames Basin, but 
may not have reached the Ouse Valley or the Lower Thames Valley. 
It has been maintained by Tutkowski’ and others that near the 
margins of great ice-sheets cold and dry conditions prevail. Outside 
this dry area the climate, although cold, is much more moist, and the 
precipitation very considerable. It may be that some of the moisture 
which does not fall near the ice margin is precipitated on the ice some 
distance from its edge owing to local winds. To some extent this 
reduced precipitation at the ice margin is a feature of the Antarctic 
Continent, for Bouvet Island, although small and out in the open 
ocean, is completely covered with ice down to the water’s edge, 
whereas the coast of the continent, hundreds of miles to the south, is 
not ice mantled to the same extent. 
It is possible that Great Britain, before the Scandinavian ice first 
reached it, was outside the dry zone and, like Bouvet Island, snifered 
intense glaciation, but that as the Scandinavian ice advanced over 
the North Sea floor towards Britain the dry zone advanced with it, 
and that when the continental ice-sheet reached our shores the air 
had become so dry that the local British ice-sheet, partly or wholly, 
melted away. ‘That such a dry period existed is shown by the 
discovery of dreikanters* in the Midland Counties. 
_ As far as can be made out, all the boulder-clays we have considered 
seem to belong to one cold period,® but this is by no means certain. 
It may be that the Bowsey and Ashley Hill gravels and some others 
to the north-east along the edge of the Chiltern Hills, in the Kennet 
Valley, and to the north-west of Bagshot, may have been formed by 
the early outflow water of the British ice-sheet ; but that the Thames, 
as suggested by Sherlock and Noble,‘ then ran past St. Albans in 
a north-easterly direction scarcely seems probable, nor is it likely 
that it passed into the Ouse Valley near Buckingham, as suggested by 
Harmer. 
Sherlock & Noble® also suggest that the Clay-with-Flints is 
a glacial deposit, ie. a boulder-clay. Now, according to the evidence 
we have, the Clay-with-Flints occurs on those portions of the Chalk 
escarpment which was never overridden by the Chalky Boulder-clay 
ice-sheet, and does not occur on those portions which have been 
overridden. There is a marked difference between the Chalk escarp- 
ment to the south-west of Luton as compared with that to the north- 
east. Sherlock & Noble remark that ‘‘an ice-sheet coming from the 
1 Scot. Geol. Mag., March, 1900. 
2 Matley, Q.J.G.S., vol. Ixviii, p. 293, 1912. 
3 Q.J.G.S., vol. xlii, pp. 439 and 466, 1886. 
4 Q.J.G.S., vol. lxviii, p. 206, 1912. 
® Tbid., p. 199. 
