72 DOMESTIC WATER SUPPLIES FOR THE FARM 



structure and texture of the water-bearing beds that the amount 

 of water which they will give up depends. A close-textured clay, 

 for instance, may hold as high as 50 per cent, while an open- 

 textured sand may hold as little as 25 per cent of its volume. 

 Notwithstanding this, a sand will ordinarily yield large sup- 

 plies, whereas a clay will yield little or no water. In quick- 

 sands water is usually present in large amounts, but owing to 

 the absence of good foundations for the curbing and the ready 

 flow of the fine sand through the minutest crevices, ordinary dug 

 wells in such material are generally out of the question and even 

 driven wells equipped with the ordinary strainers usually soon 

 become clogged. Driven or drilled wells equipped with special 

 screens and sunk by experts familiar with the various methods 

 of handling quicksand are usually the only types entirely suc- 

 cessful in such material. 



Structures, such as solution passages, bedding planes or joints, 

 play an important part in determining the yield of a well. 

 A solution passage in limestone may afford inexhaustible supplies 

 where the mass of the rock is practically destitute of water. In 

 other rocks the bedding planes and joints may afford excellent 

 supplies where no water is found in the rock itself. The amount 

 of water present in the pores of different rocks is indicated by the 

 following average porosities: Sandstones 10 per cent, shales 4 per 

 cent, limestones 5 per cent, crystalline rocks i per cent. The 

 water present in the larger openings mentioned, though small in 

 amount in comparison to that held in the pores, is yielded much 

 more rapidly and, except in sandstones and similar porous rocks, 

 usually affords the principal source of supply. 



The facility with which water enters the well depends in part 

 on the rock features enumerated and in part on the nature of the 

 well. In loose materials water accumulates most easily in stone- 

 curbed and similar types of dug wells and slightly less so in tightly 

 curbed dug wells with open bottoms. Where the water bed is a 

 strong one and the materials are sufficiently consolidated to pre- 

 vent them from entering the well the water will freely enter an 



