696 



THE COMPLETE GRAZIER. 



BOOK VIII. 



are mere drains, and (4) those maintained by condensation, the so- 

 called " dew ponds." Examples of the second class'are afforded by the 

 ponds which exist at high elevations on Chalk Downs, and which are 

 remarkable for the persistency with which they defy evaporation. 

 They are formed in, and maintained in water by, a superficial covering 

 of sand or sandy clay, which is apparently the argillaceous base of the 

 Thanet sand, or, where it is absent, of the Woolwich and Reading 

 Beds (Eocene) left adhering to the chalk. This argillaceous sand may 

 plainly be seen in and around the successful ponds, which often have 



old names. On the other hand there are 

 numerous cases of puddled ponds, resting 

 upon bare chalk on the Downs, which 

 are dry for months together. As to the 

 distinction between main springs and land 

 springs, it may be premised that a spring 

 involves the existence of water at a higher 

 level in the rock from which it flows. Land 

 springs are shallow springs due to rain 

 falling on soils, and confined* to waters con- 

 tained in or issuing from such soils, or from 

 superficial deposits of sand, gravel, or clay, 

 or other deposits which constitute the 

 " surface geology." Land springs are chiefly 

 of interest to the agriculturist, many villages 

 being still wholly dependent upon such. 

 Main springs arise from the water contained 

 in, or issuing from, all rocks constituting 

 the " solid geology." They are chiefly of 

 interest to the engineer, though not entirely 

 so, for many of the most successful ponds 

 depend upon main springs. 



Abyssinian pumps may be used with 

 great advantage in cases where the water 

 lies near the surface. Of course, it is ne- 

 cessary to pump the water before the animals 

 can drink, but the pumps and troughs are inexpensive, and take up 

 very little room. In establishing an Abyssinian tube-well, the tube is 

 driven into the ground until its perforated end reaches a stratum con- 

 taining water. The liquid will then flow through the perforations into 

 the pipe, so that, if a pump is attached at the upper end of the tube, by 

 pumping for a time all the particles of sand and fine gravel will be 

 drawn out, and the cavity thus formed will remain filled with pure 

 water, as shown in fig. 233. 



A very good way of utilising a spring from higher ground is to convey 

 the water by means of pipes to a convenient place, and run it into a 

 sunken trough, around which the ground has been made firm, so that it 

 is not trodden up by animals. A single spring may be made to supply 

 many fields, for if there are troughs connected by pipes for the water 

 to run into, very little is required for each trough. 



Fig. 233. Abyssinian 

 Pump. 



