ENGLISH AGRICULTURE. 99 



the downward passage of water, such lands cannot be wet; 

 but if such lands are wet at all it must be from the presence, 

 at some distance beneath the surface, more or less, of an 

 obstructive substratum. The presence of. an obstructive sub- 

 stratum may therefore in such a case be assumed. In some 

 cases this porous soil may be wet from rainfall upon its 

 own surface, but in more ordinary circumstances it is also 

 wet from the soakage of soils from higher lands. This is shown 

 by the accompanying diagram. The portion marked A B may 

 be considered to extend over several acres. At D there is a 

 porous soil upon which water falls and passes away, and so 

 far as the summit of the hill is concerned it is completely 

 dry. The water, however, passes downwards until it meets 

 with the obstruction at c c, and there it collects. Here 

 we have the case of a retentive soil, resting at the tail 

 of a gravel bed, and such a soil becomes wet not only 

 from the downward passage of water from direct rainfall 

 upon it, but likewise from bottom water. Water rises up- 

 wards as well as sinks downwards. Here is a case in which 

 a porous soil is not only wet from direct rainfall, but from 

 position. The first class of soils, that is the clay soils, may 

 be said to be wet from top to bottom. If we take the surface 

 of a clay field, the twenty-six or thirty inches of rain which 

 annually falls upon it is stated by our great authority, Sir John 

 Lawes, to be disposed of in the following manner seventy to 

 seventy-five per cent, is evaporated, or exhaled from the leaves 

 of growing crops, and the remaining twenty-five or sometimes 

 thirty per cent, percolates. Therefore in the rainfall of 

 thirty inches we may readily calculate how much evaporates 

 into the air and how much percolates, or is disposed of in 

 other ways. 



Impervious soils must become wet on the top. It is the 

 upper portion which will become puddled and wet with 

 rainfall to its great injury, and the water instead of passing 





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