222 ARTESIAN WELL 



fact that wells of this description were first known in North-Western Europe, in 

 the province of Artois in France, where this method of obtaining water has been 

 practised from a very early period. Properly speaking, an Artesian well is one in 

 which the water from the lower stratum rises above the surface of the superincumbent 

 impermeable stratum ; but by extension the phrase lias been applied of late years to 

 any well in which the waters of a lower stratum are enabled to riso sufficiently 

 near to the surface to allow of their being economically used. It will bo seen hero- 

 after that in many instances, borings, which wore originally strictly Artesian, have 

 at a later period lost the characteristic property of yielding waters flowing over the 

 surface. 



When the water falls upon the exposed surface of the outcrop of the permeable 

 stratum from which the supply for any Artesian well is derived, it passes under the 

 edge of the overlapping impermeable stratum, and over such inferior retentive stratum 

 as it may meet with. Then if it cannot find, or make to itself an outlet, it will 

 follow the surface of the impermeable upholding stratum, in strict accordance with 

 the laws which regulate the flow of water above ground. If, under these circum- 

 stances, an opening should be made through the overlying impermeable stratum, 

 the water will rise to a height corresponding to the level at which it passed under 

 such stratum, excepting in so far as it may be affected by friction, or by the existence 

 of any natural overflows, created by interruptions of the containing basin, or by any . 

 disturbance of the lower retentive strata of a nature to place the water-bearing stratum 

 in contact with still lower strata having no communication with the surface. 



M. Lefebvre (' Comptes Eendus de 1'Acad. des Sciences, 1838,') describes several very 

 ancient Artesian wells, which were discovered by M. Ayme in the Oasis of Thebes. 

 These appear to have been sunk through 80 feet of clay and marls, and then through 

 300 feet of limestone. M. Ayme states that in the Libyan desert, where there are 

 no rivers or springs, and upon which rain never falls, formerly a largo population was 

 supplied with water by Artesian wells, several of which have been cleared out and 

 restored by this French engineer with perfect success, The ' "Wells of Solomon,' iu 

 the plains of Tyre, are supposed to be of this description. 



The first Artesian well in London was put down in the year 1794. This description 

 of well has been used for a long period in the East and in Italy, 



The term Artesian may really be applied to all wells or borings which may be put 

 down, having for their special purpose the obtaining of water ; and the advisability 

 of endeavouring to find water by means of such wells will depend upon several 

 considerations, namely : on the quantity and quality of water required ; on the 

 physical position of the strata existing in the district where the water-supply is 

 required, and of the surface of the ground where the water-bearing rocks are known 

 to come to the surface, and on the outcrop of such rocks being denuded or covered 

 with any description of drift ; on the mechanical formation of the rocks to be perfo- 

 rated, with special reference to their compactness or porosity as the case may be, and 

 on the lithological character and thickness of the water-bearing deposit ; lastly, on 

 the application of the processes by means of which the impermeable strata can be 

 passed through, and the water-bearing strata reached. 



The first three of these considerations will now be dealt with ; the fourth point, which 

 comprises the engineering of the work, will be brought into notice under the head of 

 BOEING. Overflowing wells owe their origin, as a rule, to the infiltration of the 

 waters falling upon the surface of the globe, which, percolating through the various 

 pores and fissures of the strata, are passed into, and held by such strata of sand or 

 gravel as will contain water in very large quantities. If the water bo carried in this 

 manner from some high point on the surface of the globe to some subterranean point 

 where the surface of the ground is at a lower level than the point at which the source 

 of the water is formed, the hydrostatic pressure is sufficient in case a connection with 

 the surface is formed, either by faults or fissures in the strata, or by a borehole put 

 down from the surface, to cause the water to rise and overflow in a stream more or 

 less constant. 



In the case of all borings used for tho purpose of obtaining water, the chief consi- 

 derations are naturally^as follows.: 



1st. To obtain a certain quantity of water. 



2nd. To have such water pure. 



3rd. To have the position of the borehole so fixed as to make a constant supply 

 over a certain period of time to be depended upon. 



The site of a boring for water may of necessity have to bo fixed upon within a 

 certain limited space. The strata to be passed through, and tho physical character of 

 the surface of the ground adjacent to the site of tho boring, will probably partake of 

 one of the following conditions : 



1st. The ground to be passed through may have a Btcep inclination extending to 



