“That an abundance of water is stored up in the new red sandstone, and may be obtained, by sinking shafts and driving tunnels, about the level of low water.
“That the sandstone is generally very pervious, admitting of deep wells drawing their supply from distances exceeding one mile.
“That the permeability of the sandstone is occasionally interfered with by faults or fissures filled with argillaceous matter, sometimes rendering them partially, or wholly, water-tight.
“That neither by sinking, tunneling, nor boring, can the yield of any well be very materially and permanently increased, except so far as the contributing area may be thereby enlarged.
“That the contributing area to any given well is limited by the amount of friction experienced by the movement of the water through the fissures and pores of the sandstone; and
“That there is little or no probability of obtaining, permanently, more than about 1,000,000 or 1,200,000 gallons a day from each well, and this only when not interfered with by other deep wells.”
Statistics of the flow of the Windsor well show that the yield, in 1843, was 1,152,000 gallons per day; in May, 1848, 807,061 gallons; in January, 1850, from 705,667 to 634,752 gallons. The observations of the Green Lane well, in the same city, give the decrease in flow, per annum, at 4.7 to 6 per cent.
A plan has been proposed, by Mr. Bailey Denton, that, in order to increase the water-bearing stratum under London, sufficiently for a water supply, and also secure the well-known benefits of the filtration powers of the chalk, to let the Thames water pass down to the chalk, through the London clay, by means of wells sunk or bored. The objections raised against this plan is the possibility of the wells becoming choked by accumulation of impurities.
Mr. J. T. Fanning in his valuable “Treatise on Water Supply Engineering,” says: