8 THE NEW RAILWAY BETWEEN UPMINSTER AND ROMFORD.
sible for the most careful observer to note, with any approach to
accuracy, the limits of a terrace of river deposits cut in so soft a
formation as the London Clay. But the straight streets and open
squares of the district south of Endsleigh Gardens, in which these
excavations were made, afford much better views than usual of the
shape of the ground. And they reveal the perfect flatness of an
old river terrace, averaging originally about 75 feet above Ordnance
Datum, though now with a surface elevation of five or six feet
more, owing to the overlying "made ground." In short, the
appearance and position of this level tract seem to me to suggest
nothing whatever but an old terrace belonging to the present
Thames Valley system.
Then, if we consult the Geological Survey Map, we find that the
area between Euston Square and the river is coloured as one of old
river deposits, a little bare London Clay being shown here and there
along the course of a valley. Mr. Whitaker, in his memoir on the
"Geology of London and of part of the Thames Valley,"3 has the
following remarks on the boundary of the River Drift between the
Serpentine and the Fleet:
"The boundary-line follows the course of the Serpentine Brook
northward as far as the Great Western Railway, whence eastward by
Paddington to the southern part of Regent's Park it is doubtful. In
Mr. Mylne's map the gravel is coloured farther to the north than on
the Survey map, perhaps rightly.4 From Regent's Park the
boundary runs eastward to Euston Square, beyond which the tunnel
of the. Metropolitan Railway is in London Clay." And in another
part of this memoir (vol. ii., p. 321), we learn that at Gower, Street
Station and at Euston Square, on the Metropolitan Railway, there
was at the first-named spot, "sand and gravel with yellow clay,"
thirteen to seventeen feet, resting on the London Clay, and at
Euston Square gravel and sand up to eight feet. The made ground
at the surface varied from four to seven feet in thickness. Indeed,
in spite of the obscurity arising from the buildings and the "made
ground," which cover the surface, the Geological Surveyor has been,
on the whole, by no means at any special disadvantage hereabouts,
owing to the record of the deep and continuous sections on the
Inner Circle Railway. Thus the general evidence bearing upon the
affinities of. the beds overlying the London Clay around Endsleigh
3 Vol. i., p. 398.
4 Mr. Whitaker holds that where the boundaries of a superficial formation are doubtful, it is
better to err on the side of under-estimating the area it covers, than of over-estimating it.