250 MR. P. F, KENDALL ON A SYSTEM OF (| Aug.1902, 
275 feet across the middle of the valley. It is quite obvious that 
the valley was not cut by such runlets as now trickle through it, and 
we must seek an explanation in the diversion of the drainage by ice- 
obstruction, in the same way that similar phenomena elsewhere have 
been explained. Mr. Fox-Strangways has apparently not included 
this in his explanation of the vicissitudes of the Derwent, but 
it seems to me clear that whatever cause operated to produce 
Forge Valley, was equally in operation here to give rise to the 
Hackness gorge. 
The valley of the two Symes extends, as before remarked, to 
Harwood Dale, and it cannot be doubted, I think, that in pre-Glacial 
times whatever stream flowed in that valley must have come through 
to Burniston, and so to the sea. But the pre-Glacial drainage of 
Harwood Dale would have been less than that which now flows 
down the valley by all the captured waters from the Robin 
Hood’s Bay area, and so I think would not have produced 
unaided so large a valley as that of the Symes. If, however, we 
suppose that the Derwent also flowed in this direction, the 
difficulty is removed. ‘The Derwent flows in a course nearly 
parallel to Harwood Dale, to within a little over a mile of the West 
Syme, then turns eastward as though to make for the sea; then, after 
following this direction for about 200 yards, it turns again southward, 
and enters the great Hackness gorge, more than 300 feet deep. At 
the southerly turn it receives the stream from Harwood Dale that 
has flowed along the foot of the Corallian escarpment in a cross- 
channel, which is not only a direct continuation of the valley of 
the Symes, but resembles it closely in configuration. 
I therefore regard the Derwent as the stream primarily responsible 
for the cutting of the valley of the Symes, while the origin of the 
Hackness gorge I consider to have been somewhat as follows :— 
Before the Glacial Period, it was merely one of the many deeply-cut 
valleys which trench the Silpho and Hackness Moors, but this was 
one of the lowest. When the valley of the Symes was obstructed by 
the ice-invasion, the waters of the Derwent were impounded, together 
with those of the Harwood-Dale stream, and formed a lake which 
overflowed the rock-barrier about 550 feet above O.D., at the head 
of the Hackness gorge. With the augmented volume of water 
poured over, the barrier was cut down to such a level, before the 
withdrawal of the ice, as to prevent any resumption of the drainage 
along the old line through the valley of the Symes, which was left 
by the ice much obstructed with an infilling of Glacial deposits. 
There are two features of the Symes Valley which are peculiar 
and rather perplexing. On the north side of the valley, nearly 
as far as the transverse watershed, is a great accumulation of 
gravel in steep-sided hills, elongated in the direction of the valley. 
The most remarkable of these ‘extend for, say, half a mile about 
the Thirley-Beck Farm. To the south-east of the farm they are 
hog-backed hills of gravel some 30 feet high, with sides steeper 
than I have ever observed in any other British Drift-mounds. To the 
north-west they are much broader, and enclose a deep longitudinal 
