ON THE LEA VALLEY. 22g 



and one also the result of erosion in either Pre-Glacial or early 

 Glacial times. In this case in the valley of the Lea there is 

 quite as strong a probability against the agency of a fault as in 

 that at Littlebury ; while local chemica! dissolution, which 

 formed a possible cause on the Cam, either of making or deepening 

 the channel, is out of the question with the London-clay of the 

 Lea. 



I have already remarked that at Littlebury glacial deposits 

 are seen only on the high ground east and west of the rivei 

 valley, Boulder-clay alone having been noted there. But at 

 Newport, also on the Cam, and about three miles southward, the 

 Glacial sand and gravel is found in the sides of the valley 

 between the river-deposit at the bottom and the Boulder-clay 

 above. In the valley of the Stort this is the case everywhere 

 from its source to its junction with the Lea at Hoddesdon. 

 From Hoddesdon southward the Glacial Drift, whether gravel 

 or Boulder-clay, or both, is seen only on the high ground at 

 some distance from the river. But both on the eastern and 

 western sides of the Lea it has been noted as far south as 

 Hendon, Finchley and Muswell Hill in Middlesex, and Wood- 

 ford and Romford in Essex/ So that there can scarcely be any 

 doubt as to the Post-Glacial age of the valleys of the Cam about 

 Littlebury and the Lea at Tottenham and Walthamstow. Of 

 course I use the word Post-Glacial in its only legitimate sense 

 as meaning of later date than the Chalky Boulder-clay of Essex 

 and Middlesex. 



In the north of England, as Topley remarked in the dis- 

 cussion on Mr. Whitaker's paper, many examples are known of 

 the Pre-Glacial and Post-Glacial valleys of rivers and the 

 relations between them. In illustration he stated that in 

 Northumberland the Blyth was in Pre-Glacial times a tributary 

 of the Wansbeck, and a deep Pre-Glacial valley, which was 

 filled with Glacial Drift, occurred between the present valleys. 

 Many other cases might be mentioned in which the Pre-Glacial 

 drainage system, having been in its general features like that of 

 Post-Glacial times, the river valleys in the two periods have 

 here and there coincided. In this part of the south-east of 

 England the Glacial deposits have covered the Pre-Glacial 



4 Q-J- Geo/. Soc.. vol. Ixviii., p. 365(1892); Q J. G. S , vol. 1., p. 443 (iSg4), Also Essex 

 Naturalist, vol vii. (1893). 



