SOME OBSERVATIONS OF THE SUPERFICIAL GEOLOGY 227
of the flood plain the upper alluvium is mixed with soil washed
down from the slopes. The flood plain is largely pasture and
arable land.
From the edge of the flood plain of the Roding as far as the
road near Hobbs Cross the London Clay is exposed, though its
superficial layer contains a considerable admixture of sand and
gravel presumably derived from high level terraces of the river.
This is in contrast to the area of London Clay further west. It
is possible, however, that this may be a superficial terrace deposit
over the true London Clay. A small area of gravel and alluvium
is associated with the stream by Brook House.
The hill on which the Priory stands is capped by a glacial till
consisting of grit and quartzite erratics in a brown clay matrix.
The lower parts of the hill, however, are covered by chalky boulder
clay. This is limited on the southern side to a deposit about six
feet thick between the Hobbs Cross road and the line of trees at
about the level of the 200 foot contour, and is picked up again
on the northern side at about the same height where it extends
down the slope until cut by the two river terraces. The top of the