84 On the Sand-Pit at High Ongar, Essex.
plate to the paper in the 'Geological Magazine' I represented
by dotted lines "the great flexure, or rolling earthquake
surge," as I there (page 351) called it, from theoretical
inference only, at the very spot where the boring, made by the
Committee of the Essex County Asylum, begun ten years
after that, disclosed its actual existence, the fold in this flexure
being, of course, not shown.
In a communication to the 'Geological Magazine' for
November, 18818 I called attention to what I had thus
predicted, explaining at the same time that my study and
mapping (for my own use only) of the Glacial Beds on the
east side of England, subsequently to these papers in Phil.
Mag. for 1864, and Geol. Mag. for 1866, had shown me that
while the rectilinear ridges shown in the map annexed to my
paper on the River-valleys of the East of England, thus ==,
and as distinct from those of the arc systems, originated
during the Glacial submergence,9 I had been mistaken in
supposing the arc-disturbances to have originated during the
Glacial Period, as the position of the Glacial Beds relatively
to these arcs showed them to have originated prior to the
Glacial Period; and that I now regarded them as having
arisen from these radiating thrusts having taken place under
the old Tertiary sea, during the movement by which the
Upper Eocene or Oligocene sea-bed became land; the arcs
having acquired their character from the denudation which
occurred contiguous to the arc folded as this sea-bed emerged.
In a manuscript memoir on the subject of the Glacial and
Post-Glacial Beds which accompanies a Geological Map which
I made of sheets 1 and 2 of the Ordnance series (the first of
a set eventually made by the help of Mr. P. W. Harmer of all
those sheets between the Thames east of London, and the
north coast of Norfolk) for the purpose of showing the Glacial
8 ["Further Remarks on the Origin of the Valley System of the South-
eastern half of England, prompted by the result of a Boring near Witham,
in Essex." Geol. Mag. 1881. Decade II., vol. ii., pp. 502-504.—Ed.]
9 The lines of figs. ii., iii., iv., and v. of the plate to the first part of my
paper on the Newer Pliocene Period in England (above referred to) are
carried through these rectilinear ridges, and show the relation borne to
them by the gravel ("b") of the great submergence.