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Wash were also held up by an ice sheet and another large lake was formed, Lake
Fenland, which coincided roughly in extent with Fenland today. For a time at least
Lake Humber was connected to Lake Fenland by an overflow channel, now
marked by the dry Ancaster gap west of Sleaford, and it is probable that the
combined glacial waters of these two lakes flowed into the southern North Sea via
a Pleistocene antecedent of the present Waveney Valley.
Whilst such pro-glacial lakes are well-referenced in the literature, another
example, termed Lake Oxford by Harmer, is not generally included and again
illustrates how his geological work has either been forgotten or not known. For
instance, without mentioning Harmer, the geographers Wooldridge and Morgan
(
1937
) state:
It has been suggested that Goring Gap was initiated by the overflow of a suppositious
''Lake Oxford,'' thus uniting the Upper and Lower Thames drainage. The hypothesis
remains worthy of investigation but presents many difficulties.
Although these authors refer to 'F.W. Harmer, Q.J.G.S. 1907 (vol. 63)' in their
'Bibliographic Notes', they do not mention the title of his key paper, 'The origin of
certain cañon-like valleys' as published in the Quarterly Journal of the Geological
Society, 63, 1907, 470-513.
Following reference to some of these pro-glacial lakes and cañon-like valleys,
Harmer discussed another less acknowledged such feature which he termed, Lake
Oxford. Glacial drift pebbles found in Gloucestershire over 32 km (20 mi) from
Oxford are believed to have been deposited close to the former shore-line of this
pro-glacial lake (Richardson
1910
). Such deposits apparently provide evidence of
the extent of this glacial water body over central-southern England during the
close of the Pleistocene period due to the damming up of its waters by ice filling its
former outlet valleys.
In connection with the development of the Great Ouse basin, Harmer, following
Prestwich, suggested that prior to the glacial period, the drainage of the Oxford
region had been directed northeast towards the Wash via Bedford. However, later,
as a result of the advance of North Sea ice, this drainage was ponded back, forming
an extensive lake (Lake Oxford) which ultimately found an outlet over the Chalk
escarpment of the Chiltern Hills at Goring, diverting a large amount of drainage
into the synclinal valley of the original Thames. This was of interest to Harmer due
to its bearing on the present oversize valley of the Great Ouse and the deep
excavation of the Fenland area both of which, he believed, had been caused by the
great volume of water carried down by the river to the Wash during pre-glacial
times, that is before the drainage of the upper part of its basin had been lost by
diversion into the Thames (Harmer
1907
).
As the present Great Ouse in North Buckinghamshire appears to be too small
for its wide valley it can be described as a misfit stream with the implication that
its discharge today has in some way been reduced from that of former times. In
1947 the author witnessed the rapid transformation of this small misfit stream into
a much larger river when, due to exceptional flooding, the valley was completely
filled. This occurred in March that year when a sudden thaw of heavy winter snow
