1867.] On the future Wafer-supply of London. 53 



exhausted, the Oolitic formation — including the Coralline Oolite, and 

 the Lower Oolite of Gloucestershire, Somersetshire, and Oxford- 

 shire — forms a very large tract of water-bearing strata, from which 

 vast quantities of water might be obtained by pumping, at eleva- 

 tions varying from 400 up to 900 feet. If we project on the map 

 a right-angled triangle, having its base formed by a line stretching 

 from Salisbury Plain to the Cambridge Hills, and its apex in Kent, 

 we shall have an area of not less than 1,500 square miles of water- 

 bearing Cretaceous rocks, from which, if the whole of the water 

 which percolates were utilized (after making deductions for local 

 supply and the area covered by London clay, and loss), ought to 

 yield 150,000,000 gallons per day, giving 50 gallons per day to 

 each inhabitant of London.* 



If to the above be added the area of the Lower Oolite from its 

 outcrop to the margin of the Oxford Clay, we have a tract composed 

 of water-bearing strata of even larger extent ; but owing to irregu- 

 larities, and interruptions in its horizontal range, scarcely so well 

 adapted as the Chalk for the supply of large quantities of water 

 from wells. Nevertheless the yield from this tract might probably 

 be set down at 100,000,000 gallons per day, while very large 

 quantities could be tapped from the springs which now form the 

 sources of the Thames, Isis, and other streams. An idea of the 

 quantity of water which might be derived by pumping from the 

 southern slopes of the Cotteswold Hills may be gathered from the 

 fact, that many of the streams, owing to the porosity of the Oolite 

 rock, lessen in volume while flowing over it. Thus, it is stated that 

 the Churn loses as much as 3,000,000 gallons per day before it joins 

 the Thames at Cricklade ; | and this is only one of several others 

 similarly constituted. This water percolates into the rock, and 

 escapes in springs somewhere probably along the western slopes of 

 the hills, but certainly not into the watershed of the Thames. There 

 are also springs of extreme purity and persistence bursting forth 

 from the base of the Chalk and Upper Greensand in Berks and 

 Wiltshire, besides those which feed the Yedding, Brent, Lee, Eoding, 

 and other small streams w T hich join the Thames eastward of 

 Teddington. J To tap these springs at their sources, and conduct 

 them by pipes and open channels to the reservoirs, as also to utilize 

 to some extent by pumping the internal resources of the strata, 

 which we have shown to be ample, is not we conceive beyond the 

 power of engineering enterprise, and may perhaps be worth dis- 

 cussion before more elaborate schemes are undertaken. 



The objections to a proposal which would necessitate the 

 employment of machinery on so large a scale are obvious. A large 



* Allowing one million gallons to every five square miles of area ; deducting 

 one-third for the latter and one-fourth for the former items, 



t Mr. J. Bailey Denton : Letter to ' The Times,' October 15, 1866. % Ibid. 



