SOIL ANALYSIS AND ITS INTERPRETATION 331 



district may prove very suitable for cultivation in a cooler 

 district where evaporation is lessened Potato soils afford 

 some good illustrations ; potatoes require a light soil, but it 

 must be cool and moist. The Nutfield soil (Table LXXXV.) 

 fulfils these conditions ; it is on a slope facing northwards not 

 very far above a stream, and, therefore, does not quickly dry 

 out, hence it is very good for main crop potatoes. The 

 Tolworth soil, on the other hand, although similar in com- 

 position, is so placed that it quickly dries and is of much less 

 value. Some of the potato soils of Dunbar, analysed by 

 S. F. Ashby (jd\ have all the appearance of soils readily 

 drying out, but in their cool climate this property does not 

 show itself to an injurious extent. 



Effect of Underground Water. When the underground 

 water is near the surface, but sufficiently far below to allow 

 of proper root development, the most important property of 

 the soil becomes its power of lifting the water by surface 

 action up to the roots. The silt and sands are in such cases 

 the useful constituents, the clay and fine silt being less neces- 

 sary. The Weybridge soil (Table LXXXVI.), at about 3 feet 

 below its surface, has a current of underground water which is 

 brought to the roots by the fine and coarse sand. It therefore 

 grows excellent wheat crops. The Bagshot sands, however, 

 although similar in physical type, have in general no such 

 water-supplies and are sterile because they lack the clay 

 which, in their circumstances, could alone confer an adequate 

 power of holding water from one shower to the next. 



TABLE LXXXVI. UNDERGROUND WATER AND MECHANICAL ANALYSIS. 



The Shalford soil is a light sand with too, little power of 



