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17. — The Geology and "Water Supply of the Xeighbotjehood 



OF Watioed. 



By the Eev. James C. Clutterbuck, M.A. 



Communicated by A. T. Brett, M.D., Vice-President. 



[Read Uth May, 1876.] 



The Geology and AYater Supply of any district are so inseparably 

 connected, that it needs no excuse for considering them together. 



It is proposed in the following paper to consider the one with 

 special reference to and as depending entii'ely on the other. In 

 attempting to describe the geology of the immediate neighbour- 

 hood of "VVatford, it will not be necessary to enter into minute 

 details, but to take a general view of the subject. First as to the 

 extent of the area which may be considered the immediate neigh- 

 bourhood of Watford. Taking the Parish Church as a well-defined 

 centre, a circle with a radius of five miles will include examples of 

 the characteristic features of the geology of the greater part of 

 Hertfordshii'e, which may be described as forming a portion of the 

 northern limb of the Chalk basin of London. The river Colne in 

 its course from north-east to south-west divides the district into 

 two nearly equal parts ; that to the north-west to be accounted as 

 Chalk, that to the south and south-west presenting a band or belt of 

 the Chalk bounded on the north by the river Colne and on the south 

 by the Tertiaiy beds which overlie the Chalk ; this band varying 

 fi'om a mile to two miles and a half in width. The physical 

 featui'es of the district are to a certain extent indexes of its 

 geological conditions. The centre of the northern portion of the 

 district is intersected from north to south by the river Gade, the 

 north-western limb by the river Chess, — two rivers characteristic of 

 their origin from the Chalk, which run in deep valleys, by which 

 the otherwise slightly undulating surface of the district is furrowed. 



The Chalk, whether to the north or south of the river Colne, 

 presents little if any exposed surface, being covered by beds of 

 flint-gravel, sand, or loam, vaiying in thickness ; with the excep- 

 tion of certain isolated and outlying patches of Tertiary clay and 

 sand, in situ, which again are frequently covered with beds or 

 traces of the higher level gravel. 



To the south the Chalk, except the belt or band before men- 

 tioned, is covered by the Tertiary strata. These rise in ill-defined 

 escarpments at their junction with the Chalk. The highest levels 

 are at Bushey Heath and Stanmore Common, being capped by 

 traces of the Bagshot sands and gravel in beds of considerable 

 extent. Such is a somewhat rough description of the leading 

 geological featui-es of the immediate neighbourhood of Watford. 



The cuttings of the London and Xorth Western Ilailway furnish 

 well-defined sections of the strata more or less exposed to view. 

 Beginning with that at the southern end of the tunnel, the Chalk 

 is exposed with very remarkable undulations of surface ; the 

 cavities (sometimes called pipes) being filled with sand or gravel. 



