248 THE ESSEX NATURALIST.
spread, from the Henley loop to the Vale of St. Albans and thus
to the Essex border near Ware. If these deposits are to be
regarded as Thames gravels, then there can be no escape from
the conclusion that the Thames followed a north-easterly course
to Ware. The great stumbling-block to such an interpretation
seems to us to be the absence of any eastward gradient. The
300 ft. "terrace," if such it is, maintains its height unaltered
from the neighbourhood of Henley to the eastern end of the St.
Albans trough and the higher gravels terminate northwards at
or near the 400 ft. contour on the Chalk dip-slope throughout
this wide tract. At present these facts present an intractable
problem.
At a slightly lower level, however, there is a well-marked
terrace whose course can be traced, dropping steadily eastwards
around the northern side of the Henley loop. Whatever may
be said of the higher spreads, it can hardly be gainsaid that this
is a terrace of the Thames, for it follows the course of the river
faithfully. At Winter Hill, above Bourne End, it can be shown
that the terrace turns southward towards Maidenhead, as do
the lower Thames terraces up to and including the Boyn Hill
terrace. We propose to call this well-marked feature the
Winter Hill terrace and to regard it, as a working hypothesis
at least, as marking a stage in the excavation of the Thames
valley.
It is particularly important to notice that the Winter Hill
terrace turns southward at Bourne End, for this gives an indi-
cation of the date of initiation of the Henley loop. As already
noted, the 300 ft. gravels show no such turn, but pass on north-
eastwards. The Winter Hill terrace can readily be followed
across the block of country between the Thames at Maidenhead
and the lower Colne, and its relations to the Boyn Hill terrace
below are perfectly clear. At the line of the lower Colne valley
near Iver we reach a crucial point, for it becomes necessary to
decide whether the Winter Hill Thames turned north up the
line of the Colne, i.e., whether the Lea-Colne loop had been
initiated at this date. A consideration of the local evidence,
which must not detain us here, is definitely adverse to such a
northward turn. By the time it has reached Iver, the Winter
Hill terrace has dropped to about 200 ft. O.D. and there are
no gravels at the bend of the Colne near Rickmansworth with