kkndall: the glacier lakes of Cleveland. 
35 
to have been thrust far up the Sea-Cut. as great mounds of gravel 
at Thorn Park are probably of direct glacial origin. That this 
was the extreme advance of the ice-front seems clear, for a 
further movement westward would have obstructed the entrance 
to Forge \'alley. and the drainage would have overflowed at 
tlie next notch into Kimlin Slack, which then would have usurped 
the functions of Forge Valley. 
Tlie cutting of Forge Valley, during the maintenance of 
the ice-barrier, must have been continued to a depth not far 
short of 135 feet O.D.. as the present watershed of the drift - 
obstructed valley of the Sea-Cut reaches only that altitude. 
Otherwise the Derwent would have reverted to its old channel. 
Lake Scarborough. — The indented outline of the Oolitic 
escarpment west and south of Scarborough shows that a lake, 
or a series of lakelets, must have been held up by the advancing 
ice. Through one of the valleys — the valley through which 
the railway passes from Seamer to Scarborough — a great over- 
flow was cut (Plate XIV.). This channel is now encumbered 
with peaty matter, but borings prove the existence of a gorge- 
like glacial valley filled up with boulder-cla3\ It is probable 
that slight fluctuations of the ice-margin caused a reversal of 
drainage along the face of the escarpment, and the numerous 
lake overflows in the neighbourhood confirm this view, some 
of them draining northwards to Forge Valley, whilst others 
drain towards the Seamer Channel. 
(4) Lake Pickering. 
It is clear that the ice-sheet extended completely over 
the watershed from Scarborough to Filey, impounding the 
drainage of the great Vale of Pickering. This was the lowest 
lake of the series and for a long period received the whole of 
the drainage of the Cleveland area except, perhaps, its western 
margin, thougii even this is doubtful. 
The Vale of Pickering is a long, faulted trough of Kimeridge 
Clay, lying between the dip-slope of the Corallian Beds on the 
north, and the escarpment of the Chalk Wolds on the south. 
Eastwards it opens into Filey Bay. from whicli it is separated 
by a ridge of drift deposits, which attains a minimum heiglit 
