A DEEP CHANNEL OF DRIFT IN THE VALLEY OF THE CAM, ESSEX. 333 



19. On a Deep Channel of Drift in the Valley of the Cam, Essex. 

 By W. Whitaker, B.A., F.E.S., P.G.S. (Eead March 12, 

 1890.) 



For many years the rising-up of older rocks beneath the Cretaceous 

 beds of the London Basin, and beneath the Jurassic rocks to the 

 north and to the west, has been brought in evidence before us by 

 means of deep wells and borings. It may therefore be a welcome 

 change to notice an occurrence of an opposite kind, the evidence of 

 which is, in like manner, almost wholly owing to the well-sinker. 



In Scotland long and deep channels, filled with Drift, have been 

 noticed, and have been referred to river-action *. In the northern 

 part of England, too, the like has been observed f ; but I am not 

 aware of the occurrence of such channels in Southern England, 

 except on a small scale, having been described. It is perhaps well, 

 therefore, to bring before the Society evidence that shows a sudden 

 and deep extension downward of beds of late geologic age, namely 

 the Glacial Drift, which are usually of no very great thickness, and 

 which, in the tract in question, occur chiefly on the higher grounds. 



In the Geological Survey Memoir that treats of the part of 

 Essex that borders on Hertfordshire and Cambridgeshire, there is 

 an account of a well-section at Wenden, showing an unexampled 

 thickness of Drift at a comparatively low level, and also a descrip- 

 tion of two railway-sections that show the Drift abruptly abutting 

 against the Chalk J. 



Although my former colleague, Mr. Penning, who mapped the 

 tract in question, near Audley End, wrote that " The Drift here- 

 abouts fills an old channel, one slope of which is shown in [one] 

 section, whilst another slope in a different direction, and at a 

 distance of half a mile, is exposed near the station," he did not 

 then think the evidence clear enough to warrant further remark. 



Lately, however, a good deal more evidence has turned up, for 

 which we have to thank Mr. G. Ingold, well-sinker, of Bishop 

 Stortford. It is not proposed, however, to lay before the Society 

 the detailed accounts of the various new wells, these having already 

 been more fitly given to the Essex Field Club §. 



In the well-sections to bo referred to there is, in some cases, a 

 certain amount of Post-Glacial Drift at the top ; but this is com- 

 paratively small (in no case, for certain, more than 20 feet thick), 

 so that it may be disregarded as a separate feature, and may be 

 massed with the underlying Glacial Drift. This latter consists 



* A. Greikie, "Ancient River-courses underneath the Boulder-clay," Trans. 

 Geol. See. Glasgow, vol. i. pt. ii. pp. 49-52 (1863). J. Croll, "River Channels 

 Buried under Drift," ibid. pp. 330-345. 



t T. M. Reade, " The Buried Valley of the Mersey," Proc. Liverpool Geol. 

 Soc. Se.ssion 14, pp. 42-65 (1873), &c. 



+ " The Geology of the N.W. parts of Essex," &c., pp. 38, 39, 80 (1878). 



