556 Thames Water. 



shown by the late Professor Rogers that all springs 

 contain an appreciable proportion of common salt 

 besides other ingredients in solution. This being the 

 case, and rivers* being fed by springs that rise in rocks, 

 in addition to the water drained from the surface, it is 

 obvious that all rivers must contain various proportions 

 of substances soluble in the rocks, and, indeed, it is 

 known that even small quantities of silica may be dis- 

 solved in pure distilled water. 



The Thames is a good type of what may be done in 

 this way by a moderate-sized river, draining a country 

 which, to a great extent, is composed of calcareous 

 rocks. It rises at the Seven Springs, near the western 

 edge of, and therefore not far from the highest part of 

 the Oolitic tableland of the Cotswold Hills, and flows 

 eastward through all the Oolitic strata, composed mostly 

 of thick formations of limestone, calcareous sand, and 

 masses of clay, which often contain shelly bands and 

 scattered fossil shells. Then, bending to the south- 

 east, below Oxford, it crosses the Lower Greensand, the 

 Grault, the Upper Grreensand, all calcareous, and the 

 Chalk, the last of which may be roughly stated as 

 consisting of nearly pure limestone : then through the 

 London Clay and other strata belonging to the great 

 Eocene formations of the London basin, which are 

 nearly all more or less calcareous. The Thames may 

 therefore be expected to contain substances of various 

 kinds in solution in large quantities ; and to those 

 derived from the rocks must be added, all the impurities 

 from the drainage of the villages and towns that line 

 its banks between the Seven Springs and London. 



At Teddington, on a rough average for the year, 

 1,337 cubic feet of water (equal to 8,343 gallons) 

 pass seaward per second : and, upon analysis, it was 



