208 report— 1877. 



longitudinally down the valley-lines ; therefore, as a general ride, the flow of sub- 

 terranean water conforms to the surface-falls of the country. There are, however, 

 exceptions to this rule, as the author has found in several instances. 



An examination of a district having a number of contributing valleys shows very 

 clearly that tbe subterranean water moves down the subsidiary valleys into the 

 main valley ; and the confluence of the streams produces identically the same effect 

 in the underground channels as is observed by the junction of two streams or the 

 water flowing in two pipes. The increase of the volume of water brought into a 

 main subterranean channel from a subsidiary valley elevates the surface of the water 

 at the point of junction. This is clearly indicated by the longitudinal sections of 

 a main valley joined by contributory valleys at various points. Taking any one of 

 these examples, it is found that if a line is drawn from the surface of the water 

 at a point above where a junction is known to take place with the surface of the 

 water at another point below where the junction is effected, the result shows that 

 at every period of the year, and whether the water is rising or falling, there is 

 a considerable convexity in the longitudinal section of the water at the point at 

 which water is received. A number of examples of this character are shown in 

 making careful sections of the chalk valleys south of Croydon, particularly in a 

 valley about eight miles long, extending from Caterham to the river Wandle at 

 Croydon. Not unfrequently we find one valley runs across another, and such con- 

 tinuity of the surface may be observed which might lead to the supposition that 

 the flow of subterranean water is continuous down the valleys. This, however, is 

 not always the case, as is clearly shown by a section made above Croydon, in the 

 neighbourhood of Smitham Bottom, in the valley-line between Merstham and 

 Croydon. It might be supposed that the water flows from Merstham to Croydon ; 

 but this is not so, for the cross valley at Smitham Bottom intercepts the water and 

 conveys it away in another direction. This abstraction of the water is clearly 

 indicated by the depression in the water-line at the point where the water leaves. 

 A line drawn from a point in the water-line above the point of abstraction to a 

 point in the water-line below this point shows, during all periods, a concavity in the 

 water-surface at the point of abstraction. Where such a depression is observed it 

 is evidence of the abstraction of water. Just the same is observed by purnpin«- 

 froma well ; the water is generally lowered all round the point of abstraction. The 

 amplitude of the depression is greatest near the point of abstraction, and diminishes 

 as we leave that point. It thus becomes quite feasible to determine, by careful 

 survey, the exact direction in which subterranean water is flowing in such a dis- 

 trict as that which has recently been under the examination of the author, and also 

 to pretty accurately determine both the extent of the contributing area and the 

 probable quantity of water such an area will yield. 



A point of interest in reference to the rise of the water in the Chalk is that, takino- 

 a long valley, as, for example, the Caterham valley, observation clearly shows that 

 the water begins to rise in the wells located at the top of the valley before it rises in 

 the wells situated in the lower part of the same valley ; in fact the water in the 

 upper wells began to rise while the water in some of the" lower wells was still falling. 

 Here, again, there is a parallelism of what is observed with regard to surface- 

 streams — that the floods descend from the higher to the lower parts of the countrv. 

 _ It appears singular that the wells in the upper part of the basin should be^in to 

 rise first ; and the only solution that the author can offer for this circumstance is 

 that the rainfall is greater upon the higher lands than in the lower parts of the 

 valley; for it is quite clear that on the 25th November 1876 the water in the well 

 began to rise at Cambrian House, in the upper part of the Caterham valley, but it 

 was not until after the 3rd December that the water in the wells be°-an to rise in 

 the lower parts of the valley at Croydon ; and the water in an intermediate well at 

 the Rose and Crown Inn, Eiddlesdown, did not rise until about the 12th December. 

 In this case the water rose both in the upper and lower parts of the same valley 

 before it rose at an intermediate point. The rise in the upper part of the valley was 

 probably due to rainfall, and the rise in the lower part was probably due to the effect 

 of the united contributions of a number of short valleys discharging- into the main 

 valley. 



Another point which is deserving of attention has reference to the temperature 



