134 PRIMAEVAL MAN IN THE VALLEY OF THE LEA.
similar section through the Fillibrook stream on the other side of the
Lea in Essex as at F on the same illustration. These brooks and
streams, although they possibly follow some very ancient depression
in the London Clay beneath, are quite modem in comparison with
the age of the "Palaeolithic Floor" and its implements.
It is not a little curious that although our existing brooks are of
comparatively modern date, yet it has not been uncommon at north-
east London to see sections exposed of brooks of Palaeolithic age:
these ancient brooks became filled in with sand, and then covered
by "warp and trail" at the close of the Palaeolithic period. An
experienced eye can point out the probable position of the beds of
such obliterated underground brooks at the present day, by noticing
certain slight continuous depressions in the present ground surface.
Fig. 15.—Section through bed of a brook of Paleolithic age, tilled with stratified sand,
and covered with "warp and trail."
An underground bed of a Palaeolithic brook exists in Bayston Road,
close to West Hackney Church, Stoke Newington High Street. At
the present day it may be seen that the houses in Bayston Road
very gradually descend from both ends of the road to a very slight
depression in the middle, and this slight depression in the road
answers to the bed of an obliterated Palaeolithic brook beneath.
The section in fig. 15 is engraved to the scale of one-sixth of
an inch to the foot, copied from an excavation made in 1883, at the
south of Tyssen Road, and immediately on the west of Bayston
Road; at the base of the illustration at ABC, different strata of
implementiferous gravel and sand occur; at D the bottom of an
obliterated Palaeolithic brook is shown ; the stratum at the bottom
of the brook is deep red sand, derived from the red gravel at D;
whilst the narrow black seam which is superimposed is London clay