334 WATEE-BEAEIXG STEATA. 



of six to a maximum of five hundred cube feet per minute, 

 equal to 4J million gallons per day. 



Pumping in the chalk around London has had the effect of 

 permanently depressing the level of water, as evidenced b}^ 

 the sudden lowering of the water from an inclination of from 

 ten to fourteen feet a mile, to a sudden depression of from 

 twenty to thirty feet a mile at Kilburn. 



In the Kent district the inclination is about forty-seven 

 feet in a mile ; while between Dunstable and Hertford the 

 inclination is again fourteen feet a mile. 



Chalk absorbs water to a large extent in saturation in its 

 pores, viz ., about one-third of its bulk, that is, a cube foot cf 

 chalk will hold just over two gallons, and parts with it very 

 slowly ; the springs met with in sinking, it must be borne 

 in mind, being mainly due to free water passing along the 

 cracks and fissures which traverse it in all directions down 

 to its lowest portion. 



Before leaving the question of chalk wells, a description 

 of two bored at Southampton may be interesting. 



Trial bore-holes sunk to prove the form.ation yielding very 

 good results as to speed of work and quantity of water, it 

 was determined to sink with chisels two 6-ft. wells, 11 J feet 

 apart, centre to centre, instead of one of large diameter. 



The excavations for the engine-house over the wells was 

 made to the required depth, and at the bottom of these two 

 cast-iron cylinders, 6 ft. 6 in. diameter, were placed to form 

 entrances to the wells. 



A staging was erected above the water level, and from 

 this the work proceeded, the boring tools being lowered by 

 means of a 2-in. cable wound round a double purchase steam 

 winch, so that it tightened when the boring tools were raised 

 and slacked when they were dropped, thus giving the neces- 

 sary jumping motion to penetrate the strata. 



