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, 1881 8 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. F. 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. 
