186 SCIENCE PROGRESS. 



supply the Trafalgar Square fountains and the London 

 breweries, and we can well afford to leave them to be con- 

 verted into beer. For dietetic purposes there is no better 

 water in the kingdom than the underground water of the 

 Thames basin. For sentimental reasons I should like to 

 see it conveyed to the works of the various companies in 

 special conduits ; but we have seen that, on hygienic 

 grounds, it may safely be allowed to flow down the bed of 

 the Thames if it be afterwards efficiently filtered. 



So much for quality, now as to quantity ; the basins of 

 the Thames and Lea include an area of upwards of 5000 

 square miles. Of this rather more than one half (including 

 the Oolitic, Cretaceous, and portions of the Tertiary Forma- 

 tions) is covered by a porous soil upon a permeable water 

 bearing stratum. The remainder is occupied by the 

 Oxford, Kimmeridge, Gault, and London Clays ; being 

 thus covered by a clay soil upon a stiff and impervious 

 subsoil. 



The annual rainfall of the district is estimated at an 

 average of twenty-eight inches. The rivulets and streams 

 of the Thames basin are formed and pursue their course on 

 clay land. There are no streams on the Chalk. That 

 which falls upon this porous stratum and does not evaporate 

 sinks, mostly where it alights, and heaps itself up in the 

 water-bearing stratum below, until the latter can hold no 

 more. The water then escapes as springs at the lowest 

 available points. 



Innumerable examples of these springs occur all round 

 the edge of the Thames basin, and at various points within 

 it. Thus from the Chalk they are ejected at the lip of the 

 Gault ; and in the Oolitic area by the Fuller's Earth below 

 it, or by the Oxford Clay, geologically, above it. 



According to the guagings of the engineer of the 

 Thames Conservancy Board there passed over Teddington 

 Weir, in 1892, 387,000 millions of gallons, equal to an 

 average flow of 1060 millions of gallons daily. In the 

 following year, 1893, their passed over Teddington Weir 

 an aggregate of 324,227 millions of gallons, or a daily 

 average of 888 millions, the average for the two years being 



