H. J. L. Bcadnell—On Artesian Wells. 25 



Upper Well flowed i;>-2 u'.p.m. when Tiower Well was open (flow 50-3 g.p.m. ). 

 ,, 'JO-') ,, ,, had beeu closed 10 miuutes. 



.. -io-T „ ,, ,, 20 „ 



,. '-^O-S „ ,, ,, 30 ,, 



;i9-4 ,, ,, y, 24 hours. 



,, ,, 35-6 ,, ,, had been open 30 second.s. 



,. ,, 3'2-.'i ., ,, ,, 2 minutes. 



'i6-7 '„ ,, ,, 7 ,, 



,. 24-9 ,, ,, ,. i) ,, 



,. 23-4 ,, .. .. 16^ ,, 



19-7 ,. ., ., 45 



The rate of flo-n' of water through porous rocks has been investigated 

 by a number of engineers and geologists, among whom we may 

 mention Darcy, Hazen, King, Slichter, Knibbs, and Baldwin-Wiseman. 

 Tiie rate of flow through an underground sandstone depends upon 

 a number of conditions, the most important being the size and shape 

 of the pores between the component grains, the porosity or water- 

 holding capacity of the sandstone, the temperature of the water, and 

 the pressui'e acting on it. The yield of a well will depend not only 

 on these factors, but also on the diameter of the bore, its deptb into 

 the water-stratum, the size and number of fissures passing through 

 the bore, and last and most important of all, on the absolute height of 

 the outlet. Although some of the above conditions may be known 

 beforehand, the resistance to flow of the sti'ata immediately surrounding 

 a bore can never be more than approximately conjectured, as the size 

 and mode of arrangement of the individual grains of any arenaceous 

 sedimentary rock must alwaj's vary to a very considerable extent 

 both horizontally and vertically within compai-atively short distances, 

 and on these factors depends to a great extent the capacity of the 

 strata to transmit water. 



Considerable difference of opinion exists among geologists as regards 

 the relative importance of fissures in the production of artesian flows. 

 That fissures exist, and exist abundantly, in the Nubian Sandstone is, 

 I think, almost a matter of certainty; as I have shown in a former 

 paper, fissures arc visible to the eye in the upper sandstone (which 

 does not appear to differ in any important respect from the artesian- 

 water sandstone), and it is through them that the bulk of the sub- 

 surface water is obtained. jNIoreover, the above expei'iments appear 

 to almost demonstrate their existence, as it seems hardly conceivable 

 that the closing of a bore could markedly affect the flow of another 

 half a kilometre distant, if there were not a direct connection between 

 the two by means of fissures. 



It does not, however, necessarily follow that strongly flowing wells 

 cannot be obtained from an unfissured sandstone, for although rapid 

 .flow through a compact sandstone is impossible owing to friction, 

 which increases as the size of the channels decreases, the hydrostatic 

 pressure can never entirely disappear, the rate of loss of hydrostatic 

 head being dependent on tlie rate of flow. A rapid flow from a bore 

 does not in any way depend on an equallj' rapid flow of water through 

 the sandstone surrounding the boi'e; for instance, G.H. Knibbs, F.K. A..IS., 

 of the University of Sydney, has calculated ^ that although in a ten 



^ "The Hydraulic Aspect of tlie Artesian Problem": Proc. Roy. Soc. New- 

 South Wales, vol. xxxvii, p. 30. 



