Vol. 58.} GLACIER-LAKES IN THE CLEVELAND HILLS. 567 
130 feet; and unless the outlet had been lowered to some such 
altitude, the Drift-barrier would have been surmounted by the 
waters of the lake, and a new channel would have been rapidly cut, 
leaving the actual Kirkham-Abbey gorge as one more example 
of an abandoned channel. Testimony to the same effect is borne by 
Forge Valley, which has very narrowly escaped the resumption 
of its functions by the New Cut. The latter piece of evidence 
indeed proves that the level of Lake Pickering must have fallen 
well below this, for the fall of Forge Valley is considerable, and 
if the head of the valley was at 135 feet the outlet into Lake 
Pickering must have been much lower. 
Lake Pickering in its turn fell into Lake Humber, an extra- 
morainic lake held up in the great central valley of Yorkshire by 
an ice-dam at each of its exits. The late Prof. Carvill Lewis, 
to whom the idea of a glacier-dammed lake in this region is due, 
represented its extension in a very diagrammatic fashion in his 
maps, and showed no ice-barrier at the Wash, or even in such a 
position as to close the mouth of the Humber, but in the accom- 
panying letterpress he says explicitly, ‘The mouth of the Wash 
would be similarly qbstructed by the North-Sea Glacier.’ With 
this conclusion I entirely concur. Not only is such a lake necessi- 
tated by all the evidence regarding the extension of the ice, but the 
floor-deposits are present over an enormous area. The fine laminated 
mud, of identical character and appearance with that of the Cleve- 
land lakes, is widely distributed down the Vale of York, and far 
southward both in the Triassic valley and in the valley made by 
the outcrop of the Middle and Upper Oolitic clays in Lincolnshire ; 
but, so far as I am aware, there are no signs of beaches or deltas. 
Some other examples of floor-deposits of great interest will 
demand full consideration on another occasion, and for the present I 
must restrict myself to the question of overflows. Carvill Lewis 
boldly carried his rivers across whatever watersheds lay below the 
supposititious level of his lakes, and showed these streams as broad 
sounds 10 or 15 miles in breadth. My experience has convinced 
me that waters of such volume, with such a fall as the positions 
imply, would cut deep trenches of moderate breadth quite different 
from those which he imagined. Moreover, a lake would only under 
the rarest circumstances have two outlets operating simultaneously, 
and these never at different elevations. Now, Carvill Lewis’s Lake 
Humber is depicted with four overflows at widely different levels. 
{ mention these matters in order to make clear the way for a more 
satisfactory discussion of the problem, and not merely for the 
purpose of controverting the views expressed by Carvill Lewis, to 
whom I owe so much inspiration and encouragement in Glacial 
geology. 
In seeking an outlet for the waters of Lake Humber, I looked— 
as ‘direct overflows ’ across the Pennine range were forbidden 
alike by the altitude of the passes and the ice-bound condition of 
1 “Glacial Geology of Gt. Britain & Ireland’ 1894, p. 56. 
, 2a2 
