The Geological Survey of England and Wales. 
387 
more carefully traced, they have been represented with increasing 
fulness and accuracy upon the maps. It has been thought desirable 
to revise and complete the earlier drift surveys in the north of 
England, and to extend these surveys over the other parts of the 
country where they have not previously been made. This renewed 
examination of the ground is carried on upon maps of the scale of 
six inches to the mile, and advantage is taken of it to check, and 
where needful to correct, the already published mapping of the older 
geological formations underneath. 
As the Geological Survey advanced into the eastern counties of 
England, the importance of the drift deposits became increasingly 
manifest. Over large districts, indeed, it was impossible satisfactorily 
to delineate on maps the structure and boundaries of the formations 
underlying the drifts which spread as a deep cover above them. 
For such areas drift maps only could be issued. 
It was not until the original survey of the whole of England and 
Wales had been completed that the systematic re-survey of the 
drifts was begun on the six-inch scale, over those areas not previously 
re-surveyed for this purpose. In the south-east of England, where 
the work is under the charge of Mr. Whitaker, it has extended 
from Huntingdonshire across the counties of Bedford, Hertford, 
Buckingham, Oxford, Berks, Wilts, Hants, and the south of Sussex. 
Among the more important or interesting observations made by 
the officers in the course of these operations, the following may be 
referred to. Fresh information has been obtained as to the form of 
the land-surface on which the oldest parts of the drift deposits were 
laid down. A few years ago Mr. Whitaker described some deep 
channels excavated in the Chalk, and subsequently filled with 
Boulder Clay, in the long valley running south from Saffron Waldron. 
The River Cam now drains the northern part of this old valley, 
the River Stort the southern part. Mr. Cameron has recently noted 
a similar old channel, 100 feet deep and filled with drift, near 
Walkern in Hertfordshire. 
In regard to the Boulder Clay itself, the mapping recently carried 
on by Mr. C. Fox-Strangways in East and Central Leicestershire, 
so far as it has gone, confirms the previous observations of Mr. 
Deeley in the Trent Valley by tending to show that this deposit 
may be grouped into three fairly well-marked divisions, separated 
by sand, gravel, or brickearth. The oldest Boulder Clay seems to 
have come from the west ; the “ Chalky Boulder Clay,” which is the 
division most largely developed in this area, arrived from the east. 
This Chalky Boulder Clay is well known for the occasional great size 
of the transported masses which it contains. Mr. Fox-Strangways 
has recently noted one of exceptionally large dimensions to the 
north-west of Melton. It is a mass of Lincolnshire Oolite, at least 
300 yards long and 100 yards broad ; but it may extend beneath 
the Boulder Clay to a further distance. Quarries have been opened 
in this mass, at one place to a depth of 15 feet. Again, in the 
Boulder Clay of Huntingdonshire, Mr. Cameron has observed an 
erratic of flinty Chalk, of such large dimensions that the village of 
