228
ADDITIONAL GEOLOGICAL NOTES
resting in hollows on the Chalk. In one case at Newport, a
boring for a well for the Grammar School was begun in the
Glacial-gravel and sand. Instead, however, of the slight thick-
ness expected, "the boring tool, after passing to a depth of 340
feet, chiefly through loamy beds, did not succeed in reaching
the chalk, and the work was abandoned. The drift, therefore,
must here go down to a depth of about 140 feet below the level
of the sea, how much deeper we know not."
But the drift-filled channel which most perfectly resembled
that at "Lockwood Reservoir" is the one described by Mr.
Whitaker at Littlebury, a little more than a mile north-west of
Saffron Walden. There the valley of the Cam is cut in the
Chalk, and the Glacial Drift is to all appearance confined to the
high ground east and west of the river valley, which ranges
north and south. At the bottom of the valley are some River
Gravel and Alluvium, the village of Littlebury standing mainly
on the gravel, which is west of the stream. In five wells the
depth to the Chalk varied from 3 to 6 feet only. In two other
wells it was 15 feet from the surface ; while a third well ended
in sand at a depth of 22 feet. These wells are scattered through
the village. But near the centre of the village, and only a few
yards more easterly than the wells mentioned, a boring 218 feet
deep did not touch the Chalk, the whole of the material pierced
through being Drift. The length of this channel is doubtful, but
its direction is evidently that of the river valley, where the
surface is occupied by river-deposits, just as in the case of the
channel beneath the Lockwood reservoir.
As regards the nature of this deep channel in the Chalk,
Mr. Whitaker reviews the various explanations that suggest
themselves. These are, he says, "disturbance, sinking in of the
Chalk, and erosion." He dismisses, as extremely unlikely, the
idea of a fault, or that the gravel has filled in a hollow caused
by the local dissolution of the Chalk by chemical action, though
he admits that it may have deepened a hollow formed in some
other way, and decides that erosion of some kind must have
been the agent. And that the channel must have been cut
before the deposition of the Boulder clay on the higher ground
on each side of the river valley, in either Pre-Glacial or early
Glacial times.
It appears to me that in the channel under the "Lockwood
Reservoir" we have, in all probability, one of the same kind)