Scale 
Vol. 58.] GLACIER-LAKES 1N THE CLEVELAND HILLS. 529 
been cut below the level of the lowest part of the moraine, while the 
ice still stood against it. Ihave mentioned that a moraine, the 
highest in Eskdale, extends across the valley near Lealholm. The 
lowest point in this moraine is at most 433 feet above Ordnance- 
datum; yet there is a pair of channels, giving twofold proof that 
water was flowing from a diminished Lake Eskdale round the end 
of the moraine at altitudes exceeding 500 feet. 
The highest channel is a small, but very definite overflow, known 
as Wild Slack, which cuts the southern limb of the moraine 
immediately south of Crunkley Gill; it is not more than 20 feet deep, 
but is very well defined. It notches slightly the 525-foot contour, 
although from the gentleness of its slope I am convinced that the 
fall was very small beyond this: indeed the Slack dies out at the 
500-foot contour. It is just possible that the lake into which 
this drained overflowed by Fen Bogs, although the facts next to be 
mentioned render it very improbable. 
A small shrinkage of the ice opened a slightly lower gap in the 
moraine on the site of Crunkley Gill, where a spur of rock was 
covered by about 50 feet of Drift. A new notch was started here, 
and the level of Lake Eskdale was lowered from about 500 feet, the 
original level, down to 450 feet, when the outlet began to cut into 
live rock. By this time it had probably passed the critical level of 
the moraine, and any further withdrawal of the ice could not affect 
the position of the overflow. Subsequently, perhaps in post-Glacial 
times, the final drainage of Lake Eskdale was achieved, and the 
great gorge of Crunkley Gill, 125 feet deep, completed. 
Fig. 19.—Section across Crunkley Gall and the Leatholin moraine. 
West Mire Howe. 
Cleveland Dyke. 
Wild Slack. 
Crunkley Gill. 
LE) 
Railway. 
i) 
g/. 
Yi YY yy, yy : Te 
YY YU 
/ YY Yi 
Y 
Yi] Yy Y] i/ - ou: 
° 
rr 
° 
tesa) (a we OLS Oho OO oe 
100 200 300 400 500 Vertical 
— t Feet F 
200 400 600 800 1000 Horizontal. 
It may be objected that a simpler explanation would be to 
suppose post-Glacial denudation to have removed 100 feet of Boulder- 
Clay from the central part of the moraine. It appears to me 
exceedingly improbable, however, that such excessive denudation 
has taken place, judging by the remarkable perfection in which 
many small features of the Glacial deposits have survived. 
Moreover, the small overflow at Wild Slack demonstrates the 
existence of a constraining mass of ice. Whatever defect or 
