

Ch. XYIL] 



AETESIAN WELLS. 



389 



some 



" 



a 



instrument 



at various depths in the earth. The 

 excavating these wells is a large auger, and the cavity bored 

 is usually from three to four inches in diameter. If a hard 

 rock is met with, it is first triturated by an iron rod, and 

 the materials, being thus reduced to small fragments or 

 powder, are readily extracted. To hinder the sides of the 

 well from falling in, as also to prevent the spreading of the 

 ascending water in the surrounding soil, a jointed pipe is 

 introduced, formed of wood in Artois, but in other countries 

 more commonly of metal. It frequently happens that, after 

 passing through hundreds of feet of retentive soils, a water- 

 stratum is at length pierced, when the fluid imme- 

 diately ascends to the surface and flows over. The first rush 

 of the water up the tube is often violent, so that for a time 

 the water plays like a fountain, and then, sinking, continues 

 to flow over tranquilly, or sometimes remains stationary at a 

 certain depth below the orifice of the well. This spouting of 

 the water in the first instance is owing to the disengagement 

 of air and carbonic acid gas, both of which often bubble up 



with the water.*" 



Thames 



bored on a low tongue of land near the sea, through 300 feet 

 of the blue clay of London, below which a bed of sand and 

 pebbles was entered, belonging, doubtless, to the plastic cla} 



formation : when this stratum was pierced, the water burst 

 up with impetuosity, and filled the well. By another perfo- 

 ration at the same place, the water was found at the depth 

 of 328 feet below the surface clay ; it first rose rapidly to the 

 height of 189 feet, and then, in the course of a few hours, 

 ascended to an elevation of 8 feet above the level of the 

 ground. In 1824 a well was dup* at 



Fulham 



at the Bishop of London's, to the depth of 317 feet, which, 

 after traversing the Tertiary strata, was continued through 



6 7 feet of chalk. 



immediately 



and the discharge was about 50 gallons per minute. In the 

 garden of the Horticultural Society at Chiswick, the borings 



* Consult J. Prestwich, Water-bearing Strata around London. 1851. 

 V oorst. ) 



(Van 



