236 Notes on the London Clay and Bagshot Beds.
south-west, some remnants of pebble-beds remain,—the
pebbles enclosed in a bright reddish sand,—a specimen of
which is exhibited. These are probably remains of the
pebble-beds. At Theydon Mount and Brentwood the beds
are very similar. They are best exposed at the latter place,
where they have been extensively worked. The Bagshot
Beds in this part of Essex unfortunately appear to be entirely
unfossiliferous. The sandy beds of the London Clay at Oak-
hill Quarry have some traces of organic remains, but I have
not been fortunate enough to find any fossils. The upper
part of the dark clay is said to contain sharks' teeth and
shells, but I have seen none. I have mentioned Septaria
being found there, and these are also constant at Theydon
Mount and Brentwood;3 and from Theydon Mount I exhibit
two sharks' teeth, lent me by W. Bonner, of the brickfield
there, 1/4 mile north of Hill Hall.
In conclusion, the section at Oakhill illustrates the great
denudation which, has taken place in the river-valleys of this
neighbourhood; it shows the conformity of the beds of the
London Clay and Bagshot Sands, the latter strata being
evidently of the same formation as the Clays, revealing the
history of the beds, the deposition of which commenced in a
deep sea during a period of depression, and continued possibly
during a period of elevation. It shows, at all events, after
the deposition in deep water, a gradual shallowing until the
shore deposits, becoming more and more sandy, at last ended
in pure sand and pebbles; and these patches of sand and
pebbles on the highest grounds show the greatly extended
area formerly covered by the Bagshot Beds, of which these
isolated outliers once formed part. The dip of the beds has
yet to be ascertained, and when this is found there still
remains to be verified Mr. Searles "Wood's statement that
there are faults on the western sides of the hills. Until this
is accurately decided the actual thickness of the London Clay
at High Beach cannot be given ; it may be nearer 600 than
400 feet, but if so, it is exceptionally thick. The denuding
power of aqueous and atmospheric agencies over a soft
stratum like the London Clay is well illustrated by the
section, as well as to the amount of elevation which took
place subsequent to the deposition of the Clay. In con-
clusion, I must thank one of our members, Mr. E. Heathfield,
for assisting me in measuring and examining the beds at the
quarry.
3 The specimen of Septaria exhibited from Brentwood was remarkable
for its nucleus.