87
GEOLOGICAL NOTES IN THE NEIGH-
BOURHOOD OF ONGAR, ESSEX.
By HORACE W. MONCKTON, F.L.S., F.G.S.
THE following notes were made during the years 1887-88-89-90,
during which I had numerous opportunities of exploring the
country round Ongar when on visits to my kind friend, the late Mr.
A. H. Christie. One of the most interesting sections, and one which
I visited many times, is the sand pit, five furlongs south-east of
Chipping Ongar Castle, and three furlongs south of High Ongar Mill.
It was described by Mr. S. V. Wood in 1883 as a pit in Bagshot
Sand.1 Mr. Penning, who mapped the district, considered that the
sands belonged to the Glacial Gravel Series, and it is mapped
accordingly.
In Whitaker's "Geology of London," vol. i. (1889), it is referred
to on page 276 as a sandpit at High Ongar, and on page 314 as a pit
nearly a mile south-east of Chipping Ongar Station. Mr. Whitaker
considers it to be Glacial Drift made up of Bagshot Sand.
The section when I first saw the pit was as follows :—
1. Dark reddish earthy clay with numerous bits of broken
flint, small pebbles of flint and quartz, and some
pebbles of old rock, 2 feet to 7 feet.
2. Yellow and white sand stratified in a very irregular
manner and broken up by numerous small faults.
In one place the sand included a small patch of red
clay, 4 feet to 5 feet.
The sand bed extends from about 175 to 150 feet above ordnance
datum level, and there are small sections in it at various levels on
both sides of the road from High Ongar to Hallsford Bridge. I
agree with Mr. Whitaker that the sand is derived from the Bagshot
Beds, and that it is not Bagshot Sand in situ. I am inclined to
think that the following is its true history. There was a time before
the coming of the Boulder Clay when the Bagshot Beds extended
over all this part of the country. Through them and the underlying
London Clay the River Roding cut its valley, and the sands of the
High Ongar sand pit are the remains of a landslip which occurred
in the Roding Valley before the period of the Boulder Clay.
Subsequently the Bagshot Beds have been worn and denuded back as
1 Trans. Essex Field Club, vol. iv., p. 76.