310 THE ESSEX NATURALIST
the retreat of the ice left a wide sheet of Boulder Clay extending
north of a line from Chigwell Row to Brentwood, although a lobe
of clay is found extending south-east of Romford.
As the Thames developed its present course, a series of river
deposits were laid down which now form the gravels and brick-
earths of the Boyne Hill, the Taplow and the Flood Plain Ter-
races of the Thames.
The drainage pattern that developed on the surface of the
tills became incised so exposing the sands and clays below. To-
day these streams, Roding, Rom, Ingrebourne etc. have removed
most of the drift in the north and also much of the solid deposits
particularly the Bagshot and Claygate Beds which are now found
only on the ridges of the northern area.
The present situation is that London Clay forms the surface
of much of the area unless covered by the Thames Terrace de-
posits. The remnants of the Claygate and Bagshot beds are found
only on the ridges, sometimes covered by even smaller remnants
of the Pebble Gravel. The latest development has been the
spread of the London Suburbs outward from the south-west until
much of the Thames Terraces are covered in concrete and tar-
mac. Similarly for the rapidly expanding smaller towns of the
region.
Badger Sett Distribution
Despite having a heavy human population, setts are
generally wide-spread over the area but are more common in
the north than the south with none in the south-west quarter
verging into London. However, where setts are abundant, their