Dr. D. Woolacott—The Interglacial Problem. 31 
like in character with flat bottoms and have obviously been cut 
quickly under peculiar conditions. They breach watersheds, sever 
spurs, and trench hill-sides. Some of them cut through the drift 
into the bedrock, thus affording evidence of their origin in late 
Glacial times. Dr. Smythe has mapped about seventy in 
Northumberland, and in Durham there are many well-developed 
gorge-like examples. Owing to the Nunatakkr of the Crossfell 
ridge preventing the western ice from sweeping over South-West 
Northumberland and the west of Durham, this country was not 
glaciated to the same extent nor in the same way as the main part 
of Northumberland. (The Cheviot massif had its own local glaciers 
and its borders were swept by the Tweed ice on the north and the 
western ice on the south, and is therefore also a distinct area.) The 
glaciers in this protected region of West Durham and South-West 
Northumberland were valley-glaciers, Alpine in type, and on its 
northern and southern borders the glacier-lakes in the tributary 
valleys of the Tyne and Tees were formed on high ground, and the 
swires thus cut across high watersheds and are sometimes most 
striking in their appearance and position. In Mid-Northumberland 
the phenomena due to the retreat of the ice can, be very 
clearly studied. Dr. Smythe has shown that the line of junction 
between the Tweed—Cheviot coastal ice and the Western ice was a 
position of cleavage and weakness, and that temporary waters were 
held up on the ice-free country between these sheets as the ice- 
streams decreased, the overflow valleys and the fluvio-glacial 
Kaims being exceptionally well developed. 
(>) The glacier-lake phenomena connected with the Tees ice is 
specially interesting near Middleton. The tributary valleys of the 
Egeleshope Beck and the Blackton Burn had lakes formed in them, 
and here both direct overflow channels across the watershed between 
the Tees and Wear anda severed spur between the two minor valleys 
are clearly marked. Cutting across the ridge of Knotts Allotment 
beneath the Millstone Rigg, between the Eggleshope and Blackton 
Burns, are a well-defined series of flat-bottomed nicks, one below the 
other—notches in the spur developed by overflow marginal streams 
as the Tees glacier diminished in volume. This remarkable severed 
spur forms one of the most distinct features of the landscape between 
Barnard Castle and Middleton. It is perhaps worthy of note that 
some of these slacks afford a means of roughly determining the 
thickness of the ice in the main valley when they were formed; thus 
the trenches on this spur lie between the 1400 and 1500 contour, 
while the height of the base of the Tees valley at this point is from 
600 to 700 feet. As the highest notch was cut at the time of the 
maximum thickness of the Tees valley ice, the glacier occupying 
this valley between Middleton and Romaldkirk must have been 
700 or 800 feet thick.t 
1 The Tees valley glacier was probably held up for a time in this region by 
the Lake District (Shap) ice sweeping over Stainmoor. 
