128 RET. J. C. CLrXTERBUCK — GEOLOGY AND WATEE SUPPLY 



the existence of some fault or fissure in that direction. After 

 heavy rain the pool becomes slightly turbid, and in a chy season it 

 has been known to cease liowing over the dam by which it is con- 

 fined and over which the water usually falls. There are other 

 swallow-holes to the north and south of Bushey Grove, in the 

 direction of Hillfield Lodge, and Cold Harbour ; in the latter the 

 overflowing water might be seen this year running to waste in 

 augmentation of the floods in the rivers across the park. Again 

 there is a remarkable instance in a meadoAV through which the 

 footpath runs from ('rook Log to Bushey Church, the orifice some- 

 times being insufficient to take in all the water flowing down the 

 watercourse. "When the water thus finds its way through the 

 sand, or in some cases direct into the chalk, it here as elsewhere 

 causes a rise in the water in the chalk sometimes of 20 feet at a 

 distance of say half a mile from the river or outfall. By the slow 

 discharge of these waters that of the river is augmented, though 

 from the uncertainty due to the confined area of the chalk which 

 can receive the rainfall south of the river, the perennial flow 

 cannot be great. The amount to be calculated on as delivered fi'om 

 this source might be to a certain extent estimated by the measure- 

 ment of any wells in a line between the swallow-holes and river; 

 the wells near the river will not only rise with the irruption of the 

 water at the swallow-holes ; but whether they be shallow or deep 

 shafts sunk into the chalk, or deep borings, they will, if near the 

 river, rise and fall as the river may be flooded, or in diy seasons be 

 reduced in volume or level. 



It is well known that the Chalk and Tertiary strata, such as 

 they are seen in the district under consideration, dip towards 

 London, that their outcrop is in the bed of the Thames above 

 Woolwich, and that the lieight to which water will rise between 

 "Watford and the Thames mean tide level would be described by a 

 line di-awn from a point about 20 feet above the River Colne to 

 mean tide level in the Thames, or an inclination of about 13 feet 

 per mile, and that within a certain range near London the deep 

 wells are reduced 60 feet at the point of greatest depression, by 

 the aggregate pumping from the wells sunk into the sand of the 

 Tertiary beds and the Chalk beneath, and that when there is a rise 

 in the wells which receive the drainage of the Tertiary clay 

 through swallow-holes, the deep wells in London are also found 

 to rise. The depression of the water-level under London 60 feet 

 below Trinity high-water mark among other things shows clearly 

 the fallacy of the assertion that the water in the Chalk might be 

 aiTcsted in its passage to the sea by deep wells sunk near Watford, 

 whereas under London the drainage is absolutely reversed. 



Kow to turn to the district north of the Colne. The Chalk 

 district within the limits assigned by this paper forms but a small 

 part of an extensive area which reaches from the Colne to the 

 range of the Chilteni Hills. Though only a part of this area, the 

 water falling on its surface and given out in rivers is regulated by 

 the same laws and presents the same natural phenomena as the 



