12 NOTES ON THE GEOLOGICAL SECTION AT CHELMSFORD.
The surface of the ground at the spot where the Mammoth's
jaws were discovered in Mr. Brown's pit, is between 90 and 100 feet
above ordnance datum. The section1 there consisted of :
FEET.
Soil and very fine gravel, about 2
Yellowish brick-earth with a few pebbles here and there 4
Darkish loam with pebbles 1
passing downward into Ferruginous Gravel
(coarse), up to 2
Compact slate coloured sandy clay, with here and
there small pebbles of chalk . . . .7 seen.
We were told by the workmen that the jaws of the mammoth
had been found in the ferruginous gravel overlying the slate-coloured
sandy clay, a statement confirmed by their yellow-stained appearance
when exhibited at the evening meeting of the Essex Field Club.
Some account of this brick-earth is given in Mr. Whitaker's
Geological Survey Memoir on "The Geology of London and of Part
of the Thames Valley," vol. i., pp. 452-3. Mr. H. B. Woodward
has there drawn two sections illustrating the great irregularities in
its bedding and composition. And the late H. W. Bristow has given
the details of a section "at one of the large brickyards east of the
railway," the lowest bed in which consisted of a "pale bluish
sandy clay, with small pieces of chalk, etc.," in which the bones of
Hippopotamus had been found. This deposit is evidently much like
the lowest bed seen by us in Mr. Brown's pit west of the railway.
As to the age of this brick-earth, Mr. Woodward remarks that
though its relation to the Glacial Gravel is not clear, yet that "from
the absence, in sections of that gravel, of any similar brick-earth, and
from the position of the deposit, it seems best to regard it as Post-
Glacial."
And, indeed, I think that all the available evidence favours the
view that it is Post Glacial, or, in other words, simply a river-
deposit newer than the Chalky Boulder Clay. For while, as Mr.
Woodward remarks, sections in the Glacial Gravel have never shown
any similar brick-earth, it is very common as a river-deposit, and it
appears to me to exist just where we might expect, if anywhere, to
see a river-deposit of the kind. For, west of Chelmsford, seven
streams of various sizes unite to form the Can, which, below its
junction with the Wid, flows with a course nearly west to east. But
1 Though the section seen was as above stated, I am indebted to Mr. W. M. Webb for
pointing out that at one time there must have been seven or eight feet more brick-earth at the
surfaces as seen in adjacent pits where it is now worked.