548 



EEPORT 1882. 



tunnels at Goldstone Bottom two enormous fissures -were pierced at about IGO feet 

 distant, each of whicli delivered at once quite H million gallons per day. The 

 total length of the tunnels at Brighton is 4,200 feet, or four-fifths of a mile. The 

 quantity supplied is about 3 million gallons per day, hut the amount that can 

 be pumped daily without exhausting the wells is not less than 8 millions.^ 



Appljing these fncts to the case of the Southampton Well, it is obvious that 

 the extent of the chalk north of Southampton is much greater than that to the 

 north of Brighton. And if, as is probable, the rainfall on this area (about 1,000 

 square miles) is onlj^ partially accounted for by the rivers which flow through it, 

 it follows that a portion must escape to the sea by permeating through the mass 

 of the chalk ; and if, as elsewhere, this permeation takes place along vertical 

 fissures, there may be plenty of water in the chalk beneath Southampton, although 

 little has been found by boring, for the chance of hitting one of these fissui'es by a 

 bore-hole, 6^ inches in diameter, is obviously very small. 



We have now to consider the beds below the point reached by the boring. 



With reference to the depth of the Upper Greensand. The only place where 

 the chalk has been penetrated in the Hampshire Basin is at Chichester. It is there 

 790 feet thick. In the Southampton well 850 feet have already been passed through. 

 Since the chalk becomes thinner towards the west we might have expected that 

 the thickness at Southampton would have been less than at Chichester. At any 

 rate this consideration, taken with the fact that the boring is now in chalk with 

 seams of clay (doubtless the lower part of the chalk marl), renders it probable that 

 the chalk is now nearly peneti-ated, and that of the 20 to 50 feet estimated by Mr. 

 Ranger as still remaining to be pierced, the smaller estimate is the more probable. 

 The thickness of the upper greensand in Compton Bay and the Isle of Wight 

 generally is 150 feet, and the gault 100 feet. At Devizes and Swindon, Mr. 

 Prestwich gives the same thicknesses. Phillips also gives the gault west of 

 Devizes at 80 feet. At Petersfield the greensand and malmrock is 80 feet and the 

 gault 100. In the Vale of Wardour, Mr. Andrews estimates the upper greensand 

 at about 150 ft. and the gault at 75 ft. 



From these data we infer that the thickness of the upper greensand beneath 

 Southampton may be taken at from 100 to 150 feet, and that of the gault at about 

 100. Its area of outcrop extends around Southampton in a roughly elliptical 

 form, and distant from it from twenty to thirty and forty miles. The extents of th& 

 different areas in square miles as drawn on the Geological Survey Maps are given 

 in the following table ; also the average rainfall on the same areas (for which we- 

 are indebted to numerous local observers). Taking the absorption at one-third of 

 the rainfall, the quantity passing underground from each district is as follows : — ■ 



» These particulars are from a valuable paper by Mr. Easton (Keport of the 

 Brighton Health Congress, 1881). == Traced, and weighed to 01 of a mile. 



