LAMPLUGH: GLACIAL SECTIONS. 
249 
And another possible explanation has occurred to me, which is 
plausible enough for our purpose, and enables us to dispense with the 
services of the dubious ice sheet. 
It is this. 
Though chalk when dry and open can swallow any amount of 
water, yet when saturated and frozen, and its joints choked with ice, 
it sheds water freely, as may occasionally be seen during melting of 
the snow on the Wolds. And if. during late glacial times the chalk 
were not buried beneath the ice, we may be sure it would not escape 
the effects of the prevalent low temperature, so that the above- 
mentioned conditions would not be wanting. Therefore we may, if 
we like, assume a more or less impervious subsoil of frozen chalk 
over the whole of the Wold area ; and thus, with the aid of the wet 
weather always allowed to theorists about this time, obtain a volume 
of fresh water in the valley amply sufiScient for our requirements. 
The origin of the Wold dales and the occasional presence of 
terraced gravels along their flanks may be brought under the direct 
action of the same agency. 
Now let us return to the mouth of the valley, and consider the 
effect of the altered conditions there. 
From the head of the valley to its embouchure at Bridlington, 
there is a steady and tolerably steep gradient, but when once the 
chalk slopes are passed, and the northern end of the Holderness 
district fairly entered, the fall is absolutely lost, and there is at 
present drift ground actually higher than the valley bottom, between 
it and the sea. The present stream has cut through this, and thus 
formed the deep channel which separates Bridlington Quay from 
Hilderthorpe, by this means reaching the harbour. This channel 
has evidently been cut quite recently, as the stream now flows for 
the last half mile of its course through a mere trench in a ridge of 
boulder clay, and abandons its old gravel-flat near the corner of 
Piercy Lane. This gravel, marking out the .old course of the drainage, 
is deflected to the south west, as shown on the ground-plan, and 
spreads out, often covered by the later marls and peat, over the 
whole of the low-lying ground in the neighbourhood of Bessingby 
and Wilsthorpe, its outer edge reaching the cliff near x\ubum as 
