On the Origin of Certain Cañon-like Valleys associated with Lake-like Areas of Depression

The discovery of the Glacial origin of some gorge-like valleys in North-East Yorkshire by Mr. C. Fox Strangways and Prof. P. F. Kendall has suggested a new method of physiographical research. It is clear, moreover, that such cases must be typical and not anomalous. In all glaciated regions, whether in Great Britain or abroad, the invasion of any district by an ice-sheet, especially where its movement was upstream, would obstruct the natural drainage, producing lakes, the level of which would rise until an outlet for the water was established in some new direction. In some instances the overflow might take place over the advancing ice, or between it and the hillsides; in others, where the obstruction was of sufficient thickness, water might escape laterally, in a direction at right angles to the longest diameter of the lake and to the course of the pre-existing stream. An overflow-channel so caused, excavated rapidly by a considerable volume of swiftly-running water, would assume a gorge-like character, and originating no farther back than Glacial times would present a comparatively recent appearance. It would differ essentially from the Midland type of valley with gently-sloping contours, produced by the gradual and combined processes of atmospheric and fluviatile erosion. Typical examples ofeachkind are here given. Fig. 1 (p. 472), from a photograph taken a short distance above Bath, shows the valley ia which that city stands. :Excavated out of the Jurassic limestone of the Cotteswolds, it has rather a rapid fall, presenting, nevertheless, a characteristic example of