Vol. 58.] THE GLACIATION OF TEESPALE, WEARDALE, ETC. 587 
which took place during the phase of advance, as the ice must have 
stood successively at the same levels during both advance and 
retreat. In the whole of Upper Teesdale I have not observed any 
well-marked terminal moraine, unless the mound of clay and gravel 
at the junction of the Tees and Harwood Beck can be considered to 
be of that nature. 
The absence of terminal moraines produced during the phase of 
retreat seems to point to a very rapid removal of the ice after it had 
once ceased to be confluent with that of Kdenside. ‘The ice of 
Lunedale shrank somewhat, and then stood at a constant level for 
a considerable period; after which it seems to have disappeared 
rapidly from the valley, probably because the ice from Hdenside 
was no longer able to surmount the high watershed above Brough- 
under-Stainmoor, and the supply of the ice was thus cut off. The 
level at which the ice stood at this stable period is indicated by the 
level of the lower outlet of Lake Wemmergill. 
At the time of maximum glaciation this lake stood at a level of 
1600 feet, and overflowed by way of Merry Gill. . At a later epoch 
the ice had retreated sufficiently to allow the waters of the lake to 
escape, by way of the hollow between Merrygill-Head Moss and 
Sleight Edge (56), and the large size and great depth (about 75 feet) 
of this channel bear witness to the long time during which the ice 
stood at this level. 
The valley is now quite streamless; and although the floor con- 
sists of limestone, the fact of its dryness cannot be attributed to the 
absorption of a former surface-stream by the rock, as there is no 
catchment at the head of the channel capable of yielding a stream 
competent to produce so large a valley. ‘The waters of the lake 
overflowing by this channel at a height of 1475 feet, produced a 
large gravel-fan above the farm of Low Wythes (57). This halt 
of the ice during its retreat is not confined to Lunedale, but is 
just’ as well marked in Teesdale itself. 
The best evidence in Teesdale is te be seen on the _ basalt- 
escarpment which runs along the Yorkshire side of the valiey 
opposite Middleton-in-Teesdale, and extends to High Force. During 
the stable period the ice appears to have filled the inner valley, but 
to have been unable to surmount the basalt-cliffs. The result of 
this was that a system of streams was produced, flowing parallel 
to the side of the glacier, along the summit of the cliffs. . 
These streams have left records of their presence in a series of 
gorges and channels which run parallel to the line of cliffs, in some 
cases only a few yards from their edge. The summit of this line of 
cliffs at its northern end is at a level of 1175 feet, while opposite 
Middleton it stands at about 1000 feet. A series of gorges cut 
back into this cliff-line, approximately at right angles to its face. 
These gorges have very steep sides, and the streams which 
occupy them have very steep gradients; they have been started by 
the ordinary drainage of the wide outer valley, the floor of which 
is formed in this region by the upper surface of the basalt-sill. 
Connecting these normal valleys with each other is a series of 
