1 8 SiMALL WATER SUPPLIES. 



Now, besides being very absorptive, chalk is very 

 retentive. It is intersected with fissures along which 

 the water travels by capillary attraction, hence 

 although from chalk when exposed water will rapidly 

 evaporate, yet percolation is not the means by which 

 a supply can be looked for. Again, when chalk is 

 very low down below the surface it becomes subjected 

 to a superincumbent load, which tends to close up 

 these fissures, and the abstraction of water therefrom 

 is rendered more difficult, and borings in chalk are 

 generally made where (or near where) it outcrops at 

 the surface. On chalk beds near the sea the capil- 



Escarpment 



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Gaidt 



FlG. 6. 



lary attraction of the chalk will even cause an inflow 

 of salt water, and the supply from any wells in the 

 district may be brackish. Chalk, however, generally 

 lies in basins, the edge of which will be found to be 

 intercepted by rivers and sometimes by the sea. A 

 typical example is shown in fig. 6, in which the chalk 

 is on the surface overlying a bed of marl superim- 

 posed on greensand and gault clay. The probable 

 position of springs is shown. The surface of satura- 

 tion slopes at about i in 400. In cases of this kind 

 water obtained in this manner is usually of -finer 

 quality. The steep slope of the chalk shown in fig. 

 6 is known as the escarpment side. In fact, this is 



