6
THE ESSEX NATURALIST.
apart from picking up one or two flaked pieces that were lying
about, I saw nothing but the form of the bench with the wall
of country rock behind: which, I think, within certain limits,
tells its own story.
Solifluxion.—Interesting examples of sub-soil sliding are
often revealed in temporary excavations in a London Clay
country. For example, a section up to a depth of 3 or 4 feet will
show brown clay which one would naturally assume to be the
top of the London Clay, substantially in place apart from
weathering; whereas a section of twice that depth may show,
in the lower part, gravel in irregular pockets or strata dipping
at all angles. The A.R.P. trenches in Loughton, at the foot
of the hill going up to High Beach, were an illustration of this.
The solifluxion deposit known as the Trail, which belongs
to a late stage of the Pleistocene, as it overlies the Palaeolithic
river deposits, is a ubiquitous trap when collecting implements
from pits. This deposit is extremely irregular, it passes over
hills and valleys alike, and frequently plunges down as much
as 10 feet, or more from the surface. It introduces relics deeply
into the ground that do not belong to the main deposit present
there, and some may be earlier and others later. The literature
of Prehistory is full of questionable records of implements that
probably came from this deceptive Trail, rather than from the
main deposit present at the spot; or, if not from the Trail, from
some subsequent rearrangement or obscure remnant of a later
deposit.
Another fruitful source of error in the case of implements
purchased from workmen is the widespread custom of passing
implements on from one pit to another for sale. Moreover, when
relics are brought to museums for sale, a false locality is some-
times deliberately given, and duly recorded, in order to maintain
the secrecy of the actual hunting ground.
Correlation: the Date of the Lea Valley Tundra
Deposits.—On the general problem of correlation we are still
very far from having established the geological phases to which
the prehistoric industries belong, and, for my part, I have no
fixed scheme of correlation between the one and the other.
Worthington Smith referred his important discovery of the
Stoke Newington "floor" to the Mousterian Cave industry. We