Geoscience Reference
In-Depth Information
In suggesting possible pre-glacial drainage patterns for eastern England, Har-
mer anticipated current research regarding the reconstruction of pre-glacial river
systems which has shown that the region was drained by a major easterly flowing
river (possibly the Pleistocene 'Bytham River') which joined the North Sea near
Lowestoft (Bricker et al.
2012
). However, recent research has shown that the
'Bytham River' could not have existed in the form earlier suggested and that
further examination of ancient drainage patterns in eastern England needs to be
undertaken (Gibbard et al.
2013
). With his studies of variations in river flow before
and during the glacial epoch, Harmer would certainly have been interested to know
that the subject of variations in drainage patterns is currently being investigated by
British geologists.
Harmer also suggested that it would be interesting to investigate whether the
origin of two notable gaps in the Jurassic escarpment at Lincoln and Ancaster,
which connect in an apparently artificial manner, the basins of the Trent and the
Lower Witham, could be explained by applying the theory he had proposed
concerning major changes in river drainage due to ice-sheet action. Writing with
reference to Harmer's theory, Jukes-Browne stated:
The Honington [Ancaster] gap is, in fact, one end of a transverse valley which cuts
through the Jurassic escarpment, and the tract of gravel west of Ancaster is now the
watershed between the Honington Beck flowing westward and a nameless beck flowing
eastward to Sleaford. Like most other transverse valleys, it probably owes its origin to a
stream which ran eastward across the Jurassic area before the escarpment was developed,
and in that case it would be of pre-glacial age. Mr. F.W. Harmer (1907), however, has
recently suggested that both the Honington [Ancaster] and the Lincoln gaps were formed
during the Glacial epoch by the overflow of a large lake [Lake Humber] the formation of
such a lake being due to the advance of a massive ice-sheet from the north which dammed
up the outlet of the Trent and other rivers.
Mr. Harmer thinks that the lake so formed first found an outlet at Lincoln, and when this
was blocked by the further advance of the ice a second one was formed along the
Honington [Ancaster] gap. The exact way, however, in which these two gaps were formed
has nothing to do with the inference from the disposition of the gravels that in early post-
Glacial time the Witham ran through the Honington [Ancaster] gap and not through that at
Lincoln. .. In the same way there can be little doubt that at the time when the Witham
flowed through the Honington and Ancaster valleys the Trent flowed through the Lincoln
gap (Jukes-Browne 1910).
3.6 The Pre-glacial Course of the Thames
In early and middle Pleistocene times (about a million years ago) the Oxford basin
was drained by two rivers, the proto-Thames and its tributary, the Bytham with the
proto-Thames flowing northeastwards. During the Anglian cold stage of the last
glaciation, ice sheets to the north were melting and a pro-glacial lake was formed
to the north of Goring (termed Lake Oxford by Harmer); later its overflow channel
