220 FIELD GEOLOGY. 



rainfall occurred in the Lake District, in 1872 ; 

 in the Southern and Eastern counties, in the 

 same year, it was 27 inches. The rainfall of 

 1872 was 36 per cent, above, and of 1870 18 per 

 cent, below the average. 



One very large portion of the rainfall runs away in 

 rivers to the sea ; another is given back again by evapo- 

 ration. But in every year and in every locality there 

 remains, as stated above, a quantity which, economised 

 and utilised, would be much in excess of our require- 

 ments. And this quantity finds its way into the hidden 

 recesses of the earth, to be given or drawn forth from 

 the natural and artificial founts described in the follow- 

 ing sections (2 and 3). In proportion to the size of the 

 collecting area will be the quantity, and according to 

 the nature of the strata through which it passes will be 

 the quality of the water supplied. 



2. Streams and Springs. The water-supply of a 

 district is not, by any means, necessarily proportionate 

 to its rainfall. So much depends upon its physical 

 geography, its height above the seaj and especially upon 

 the nature of its soils, subsoils, and underlying strata. 

 So far as natural founts are concerned, the valleys will 

 be better off than the hills, and the low-lying districts 

 than those of greater elevation ; while permeable soils 

 and subsoils receive, and for a while retain, a much 

 larger quantity of water than do those that are imper- 

 meable. For, as the rain falls on the ground, it is 

 drawn by the law of gravitation to a lower level ; if the 

 surface be impervious, it runs off by the ditches and 

 rivulets to the larger rivers, and thence to the sea. If 

 the surface be wholly or partly pervious, a portion only 



