WELLS AND WELL SINKING. 29 



pf a good supply ; in the same way as dykes of 

 igneous rock in porous strata present a barrier in 

 the course of the flow of water along its natural 

 slope, and tend to force it upwards along the line 

 of this barrier. 



First of all let us consider wells of somewhat 

 large diameter and shallow depths in comparatively 

 soft earth. The practice generally consists of ex- 

 cavating the hole and lining it with brickwork, iron 

 or concrete as the case may be, the latter process 

 being technically known as steining, and is not re- 

 quired in hard rock and firm chalk. Those wells 

 in soft earth are for obvious reasons nearly always 

 circular, although the oval form seems to have found 

 favour with some engineers. 1 The excavation in 

 such cases is the same as any other engineering 

 work, shoring and strutting being required on loose" 

 sand and soft wet clay and loam, and any water 

 gaining access to the workings requiring removal, 

 or the use of cast-iron segments to keep it out. 

 Water of this description is especially liable to be 

 met with in sand springs present in plastic clay. 

 Boring will probably have to be resorted to in such 

 cases. The simplest case of a well is that sunk into 

 a bed of sand or gravel which rests on a bed of clay, 

 and this constitutes a shallow well. Such wells 

 generally reach a depth in the sand or gravel which 

 is permanently in a state of saturation, and this level 

 is generally above the clay. No estimation of the 

 depth can be formed with accuracy ; theoretically it 

 corresponds with the level of the lowest natural 



1 The use of the oval well is usually confined to cases where extra 

 width is required to place two pumps abreast. 



