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 80,^3 4 JUL 20 1^42 y 



OF THE Jr^^j ^^^ 



HKRTFOIIDSHIRE NATURAL HISTORY SOCIETY. 



I. 



THE RIVER-SYSTEM OF WESTERN HERTFORDSHIRE. 

 By Alfred Sutton, Assoc. E.S.M. 



Read at Watford, '22,rd October, 1905. 



Thk records of the Hertfordshire Natural History Society 

 contain several references to certain of the rivers of the county, 

 and a general description of them occurs in Mr. Hopkinson's 

 Introduction to Pryor's ' Flora of Hertfordshire,' l)ut the system 

 presents features of interest in relation to modern theories of 

 river- development which do not appear to have been specially 

 treated. It is the object of this paper to point out the bearing 

 of these theories in considering the development of this particular 

 system, and to suggest certain possible solutions of the problems 

 which present themselves, rather than to set forth the results of 

 my own investigations into the subject. 



The whole of western Hertfordshire, except two small portions, 

 one at the extreme north-west beyond Tring, and the other at 

 the south near Barnet, drains into the Colne, so that we are 

 concerned only with the head- waters and tributaries of a single 

 river, and indeed mainly with its upper, though principal, 

 tributaries, the Chess, the Gade, the Bulbourne, and the Ver. 

 These tributary streams all rise near the escarpment of the 

 Chalk in the Chilterns and adjacent hills. Thence they flow in 

 a general south-easterly direction until they are confronted by 

 the barrier of the Tertiary beds which rises along the Middlesex 

 border. They then unite in the Colne, which flows first south- 

 west along the outcrop of the Chalk, and then south through the 

 Chalk to join the Thames at Staines. The area they drain must 

 formerly have been much more extensive than it is now, for the 

 dip -slope down which they flow clearly extended much farther 

 to the north-west, and indeed Professor Eamsay gave it as his 

 opinion that the Chalk formation extended originally over the 

 Oolites away to the mountains of Wales. 



VOL. XIII. — PART I. 1 



