Dr. D. Woolacott—The Interglacial Problem. 29 
the Cheviots,! and in the tributary valleys of the Tyne and Tees.? 
The overflow channels connected with the latter are one of the most 
marked physiographical features of South-West Northumberland and 
Western Durham. The glacier-lake of the Derwent valley? was 
formed when the Lake District-Northumberland ice was feeling the 
pressure of the coastal ice many miles inland. 
(8) The phenomena connected with the period of ice-retreat are 
specially well-marked in Northumberland, and have been very 
carefully worked out by Smythe.‘ He has proved that the first 
ice to retreat in that country was the western flow from South-West 
Scotland and the Lake District, while the Tweed—Cheviot ice still 
occupied the coastal border.’ A system of temporary lakes was 
formed ; the numerous overflow channels from these and the Kaims 
deposited by streams flowing into them from the free margin of the 
ice-sheets are among the most distinctive features of the physical 
geography of Mid-Northumberland. About the same time the gap 
at Ferryhill was cut by a stream flowing from waters held up by 
ice in the Tees valley,® and the gorge of the Wear near its mouth 
was probably started by an overflow stream when the Tweed— 
Cheviot ice was holding up temporary waters to the west and finally 
retreating from North-East Durham. Further to the west the 
phenomena connected with the retreat of the ice are also in places 
clearly observable. Beyond the limits of Western Northumberland 
the retreating ice held up waters of some magnitude, the overflow 
channel from which is the great swire of the Tyne Gap.’ The 
retreat of the Lake District (Shap) ice across Stainmoor is distinctly 
marked on Cotherstone Moor by the well-developed group of Kaims 
known as the Burners Hills. The contrast between these conical 
fluvio-glacial mounds and the flat-topped table-like Millstone Grit 
hills—butte- or mesa-like remnants of a small dissected plateau—ot 
Goldsborough and Shacklesborough on either side of them forms 
one of the distinct features of the country lying between Barnard 
Castle, Bowes, and Middleton-in-Teesdale. 
(9) While the position of many valleys now dry or still drainage 
channels was determined by the overflow channels from glacier- 
1 Kendall & Muff, Trans. Edin. Geol. Soc., vol. viii, 1902, pp. 226-30; 
Woolacott, Geogr. Journ., July, 1907; Smythe, Glacial Geology of 
‘Northumberland, 1912. 
2 Dwerryhouse, ‘‘ Glaciation of Teesdale,” etc.: Quart. Journ. Geol. Soc., 
vol. lviii, 1902, pp. 572-608. 
3 Herdman, “ Glacial Phenomena of the Vale of Derwent” : Proc. Univ. 
Durham Phil. Soc., vol. iii, pt. ii, 1909. 
4 Glacial Geology of Northumberland, 1912. 
® [bid., p. 104 
6 Woolacott, Geogr. Journ., 1907, p. 43, and Trechmann, op. jam cit., Quart. 
Journ. Geol. Soc., 1920, p. 192. 
7 Smythe, @lacial Geology of Northumberland, p. 106, The course of 
this valley was probably first of all determined in Preglacial times by the 
Irthing, which appears to have been then a tributary of the South Tyne. 
Woolacott, Geogr. Journ., July, 1909, p. 8. 
