24 KENDALL : THE (iLACIER LAKES OF CLEVELAND. 
Tlie levels show that the ice-barriers stood simultaneously 
here and at the gap in the Lealholm moraine, for the cutting 
commenced at Sunny Brake at a level above that at which the 
Lealholm gap would have been open. Between Crunkley Gill 
and Sunny Brake a narrow marginal lake probabty extended, 
much of it more river than lake. 
A third significant gorge occurs at Glaisdale, less than half 
a mile below Sunny Brake. Here the Esk has cut a deep gorge 
into the rock to evade a morainic obstruction, although the 
moraine is of less height (325 feet O.D.) than the top of the gorge, 
which is distant only 300 yards. (See maj), Plate XIV.) 
The three examples, Crunkley Gill, Sunny-Brake Slack, and 
Glaisdale, show that an ice-obstruction extended across Eskdale 
at the same time that a free fall for water could be obtained at 
the levels which I have indicated, namely, for Crunkley Gill, 
500 down to 450 feet ; Sunny Brake, 475 down to below 400 
feet ; and Glaisdale. about 350 down to 325 feet. 
Where, now, was the actual escape southwards ? 
One of the peculiarities of the Fen Bog overflow is that it is- 
the lowest outlet from Eskdale. saving only Whitby Harbour, 
and that appears to have been the actual outlet. This, of course, 
need not imply that the coast at W^hitby was free from the edge 
of the ice, for the cutting of the gorge may have been merely 
commenced at this stage, and marine erosion on this coast has 
no doubt removed a strip a mile or two in breadth since the 
Glacial Period. But there must have been a free fall to the 
southward, and this can have been obtained only by low-level 
channels in a coast- tract since carried away, or by actual open 
water. 
The stages of ice-retreat in Eskdale are indicated by a series 
of morainic ridges of sand and gravel that descend from the 
northern moors across Eskdale at Glaisdale. and a further chapter 
in the Glacial history of this district is ver}^ clearly recorded by 
a series of overflow channels cutting through the northern water- 
shed above Egton Bridge. 
The retreat of the ice from Eskdale carried the melting 
front, step by step, backward up the northern slopes of the Esk 
Valley, until it fell entirely behind the crest. It withdrew 
