470 MR. F. W. HARMER ON THE [Nov. T907, 



29. On the Oejgin of Certain Canon-like Valleys associated with 

 Lake-like Areas of Depression. By Frederic William. 

 Harmer, F.G.S., F.R.Met.S. (Read May 15th, 1907.) 



[Plates XXXI-XXXV— Maps & Sections.] 



Contents. 



Page 



I. Introductory 470 



II. Lake Pickering and the Malton Gorge 475 



III. The Cheshire Plain and the Gorge at Ironbridge 477 



IV. Marrington Dingle 481 



V. A suggested Lake Trowbridge and the Gorges at Clifton 



and Bradford-on-Avon 483 



VI. The Gaps in the Jurassic Escarpment at Lincoln and 



Ancaster 486 



VII. The Chalky Boulder-Clav of Lincolnshire and the Mid- 

 lands ". 490 



VIII. A suggested Lake Oxford and the Goring Gap 494 



IX. The Pleistocene Erosion 506 



X. The Chalky Boulder-Clay and the Chalk-Escarpment ... 507 



XL General Considerations 510 



I. Introductory. 



The discovery of the Glacial origin of some gorge-like valleys in 

 North-East Yorkshire by Mr. C. Fox Strangways l and Prof. P. F. 

 Kendall 2 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 con- 

 siderable 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 



1 ' Jurassic Rocks of Britain : Yorkshire ' Mem. Geol. Surv. vol. i (1892) 

 p. 419 ; & Trans. Leicester Lit. & Phil. Soc. n. s. vol. iii (1894) p. 333. 



2 Quart. Journ. Geol. Soc. vol. lviii (1902) p. 471. The subject was also 

 discussed by the late Prof. H. Carvill Lewis at the Manchester Meeting of 

 the British Association in 1887 (Report, p. 692), and more recently by 

 Mr. F. R. Cowper Reed in 1901 (' Geological History of the Rivers of East 

 Yorkshire '). 



