224 ARTESIAN WELL 



Where gmvol only is found, water cannot generally bo procured by short holes, but 

 whore gravel rests on an impervious clay, success is almost certain. 



In cases where there is apparently a considerable hydrostatic pressure, there is a 

 condition which will prevent any largo quantity of water falling upon porous strati, 

 passing to subterranean depths. Should any river emanate from, or pass through, 

 such strata, the river will probably carry away a large proportion of the water which 

 otherwise would have saturated the permeable rocks. 



It will be understood that the geological formations in which Artesian explorations 

 can bo made with most prospects of success are those which combine compact and 

 impermeable strata with porous and open rocks. The particular systems of rocks 

 which appear to present as a rule these conditions are those contained by and lying 

 adjacent to the chalk series, embracing the London clay, the chalk, upper grecnsand, 

 the gault, and the lower greensand. These rocks present the necessary conditions, 

 and in the sites where they are chiefly found, the north of Franco and south-east of 

 England, a large number of wells have been put down, many of which are producing 

 largo volumes of water. 



In older formations it is much more difficult to discover rocks of sufficient openness 

 to carry large quantities of water, and further than this, as the older rocks lie very 

 irregularly, and frequently at a heavy inclination, they are not so suitable for tho 

 purpose of obtaining water by moans of boring. Hence it is usual in districts where 

 such rocks prevail to obtain tho water-supply, where river-water either is not used or 

 is not obtainable, from reservoirs situated at some high level where they can bo 

 arranged to catch tho surface-drainage. 



The hot springs which burst out of the ground in districts whero the so-called 

 primary formations are found, came undoubtedly from a great depth beneath the 

 surface, and derive their heat from an exalted subterranean temperature ; but it 

 would not be practicable to bore to such extreme depths as would be necessary in these 

 rocks. A miniature representation of such springs is exhibited in tho intermitting 

 fountains of fresh water on the shoulder of Vesuvius. 



It will be interesting to record the results of some of the chief artesian borings 

 which have been made in this and other countries. The most famous example is that 

 of the boring commenced in 1833 at Crenelle, a suburb of the SW. of Paris whero there 

 was a great scarcity of water. Here the chalk was overlaid by gravels, marls, and clays, 

 which were known to bo capable of intercepting tho passage of water. Hence, as it 

 was known that below tho chalk water-bearing sand would be met with, M. Mulot, tho 

 engineer of tho well, supported by the authority of MM. Arago and Walferdin, 

 resolved to seek a supply of water by boring through the chalk into the sub-cretaceous 

 strata. At Elboeuf the chalk had been traversed in this manner, and the water had 

 risen to a height of 82 feet above tho level of tho ground, or 109 feet above the level 

 of the sea, and it was considered that as the surface of the ground at Crenelle was 

 about 104 feet above the level of tho sea, and as the outcrop of tho water-bearing 

 strata was nearer to tho proposed borehole than at Elbceuf, tho water at Crenelle 

 might be expected to flow over the surface. This reasoning was found to bo correct, 

 and in February, 1841, after eight years' labour, the rods suddenly descended several 

 yards, having pierced into the vault of tho subterranean waters so long sought after 

 by the indefatigable engineer. A few hours afterwards he was rewarded for all his 

 anxious toils ; for tho water, rising to the surface, discharged itself at the rate of 

 881,884 gallons in every twenty-four hours ; the temperature of tho water being 

 nearly 82 F. At first it brought up so great a quantity of sand that the tube was 

 several times choked up by it, and even now it is not free from occasional though 

 rare interruptions, but tho force of tho column of water has always proved sufficient 

 to clear its way after a short interval. The water flows in a clear, continuous stream, 

 and is carried by pipes to a reservoir near tho Pantheon, whence it is distributed over 

 the adjacent parts of the city, as well as along tho lino of the Boulevards from tho 

 abattoir to the Observatory. By means of small pipes, the Ecole Militaire, the Inva- 

 lides, and two or three other public establishments, are also supplied with this water. 

 The surface of tho ground at tho well is 102 feet above the level of the sea, and the 

 water is capable of being carried above this to a height of 120 feet. The exposed 

 surface of tho water-bearing beds which supply the well of Crenelle is about 117 

 square miles ; the subterranean area in connection with these lines of outcrop may 

 possibly be about 20,000 square miles, and tho average thickness of the sand of the 

 gres verts, serving in their underground range as a reservoir for the water, does not 

 probably exceed thirty or forty feet. Prestwich on the Water-bearing Strata of 

 London. 



After the completion of the Crenelle well others were quickly undertaken. Amongst 

 tho most important of these were the borings undertaken in tho Khenish provinces 

 for bringing to tho surface the waters of the brine-springs of that district, some of 



