U 
rome 
Vol. 58.] GLACIER-LAKES IN THE CLEVELAND HILLS, 593 
The pre-Glacial drainage-lines of this region differed in one 
very material respect from those now followed—the great wide 
valley of the Sea Cut which passes between the Corallian blocks of 
Suffield and Seamer Moors was occupied by a large stream, con- 
sisting of the confluent waters of the Black Beck, Sow Beck, Kirk 
Beck, and the stream which flowed down the Hackness Valley 
before the overflow of the Derwent. It is not improbable that the 
Sea-Cut valley remained open after the closure of the corresponding 
valley to the north, that of the two Symes. In that case the 
drainage of the whole country from Iburndale southward would, 
after passing into a lake at Harwood Dale, overflow down the 
Hackness gorge and come through the Sea Cut, but not even then 
would it obtain direct access to the sea. 
An advance of the ice-front to the Ragebron escarpment near 
Seamer Beacon would impound the drainage of the Sea-Cut valley. 
producing a lake, which may (for convenience) be referred to as the 
Hackness Lake. When the waters rose to about 400 or 425 feet 
O.D., the lowest gap in the Corallian escarpment, which was at 
Spikers Hill, would be surmounted, and a large volume of water 
would flow down the dip-slope of the Corallian rocks towards West 
Ayton, in the Vale of Pickering. I do not think that any con- 
siderable valley existed previously on this line, the contour of the 
country seeming opposed to such a view. 
The line of drainage thus initiated was rapidly deepened and a 
veritable cafion, Forge Valley, produced, which in the sharpness 
of its lines surpasses even the Hackness gorge. Some features of 
the emergence of the Glacial torrent into the Vale of Pickering will 
be described a little later (p:,557)s 
An ice-lobe appears to have penetrated far up the Sea-Cut valley, 
and I am disposed to regard the great mounds of gravel at Thorn 
Park, close to the Derwent, as of direct Glacial origin ; but I do not 
think that the ice advanced much beyond this point, for there is a 
second low gap in the Corallian watershed less than three-quarters 
of a mile beyond the entrance to Forge Valley, and had the invading 
lobe reached this point, Kimlin Slack would have usurped the 
functions of Forge Valley. The cutting of the last-named valley 
must have proceeded, during the maintenance of the ice-barrier, 
to a depth not far short of 135 feet O.D., as the present watershed of 
the Drift-obstructed valley of the Sea Cut only reaches that alti- 
tude, and a great artificial drain has been cut through from the 
Derwent to Scalby Beck, by which a considerable volume of water 
is discharged at normal seasons, and still more when the Derwent 
is in flood. Unless Forge Valley had been cut as deep as this, the 
Derwent would have reverted to the old channel. 
We may now consider the Glacial drainage of the Scarborough 
embayment. 
The Oolitic escarpment is much indented between the north-eastern 
angle of Seamer Moor and Wheatcroft, a hamlet about 1 mile east 
of Scarborough. Many deep valleys existed hereabouts in pre-Glacial 
