Artesian Wells. 391 



In localities disturbed by volcanic upheavel, or by the more 

 lateral thrusts of cmstal movements due to secular refrigeration^ 

 faults and folding of the strata make the selection much more difficult 

 and uncertain than in regions where the rocks lie more or less as they 

 were deposited, because the faults and fissures lead the underground 

 water in directions impossible to estimate at the surface, and often 

 to inaccessible depths ; and it requires considerable experience, allied 

 with keen observation, to determine on favourable situations for 

 boring. By sinking a number of boreholes in it, a practical acquaint- 

 ance with a formation may be gained, which is of great value in this 

 work, and the local knowledge of the occupiers of the land is often 

 of assistance. 



GEOLOGICAL CONSIDERATIONS. 



In the younger rocks of the Karroo, where the beds of sandstone 

 and shale are almost horizontal and are traversed in all directions by 

 dykes of igneous rock, the selection of sites is fairly easy, as the im- 

 pervious dolerite obstructs the flow of subterranean water and 

 encloses .spaces of various areas forming underground tanks, which, 

 if the strata have any inclination and the denuded ends of the porous 

 sandstone beds are exposed, act as true artesian areas. An examina- 

 tion of the dip and strike of the strata and of the position of the 

 walls of impervious rock point to a situation for a borehole which will 

 drain the whole of the enclosed underground area, and, under favour- 

 able conditions, flow at the surface. But among the older rocks of 

 the South and West of the Colony, besides the supplies nearer the 

 surface, there would appear to be water stored in the trough-like folds, 

 due to earth-movements, lying, however, at considerable depths, 

 which, if it could be tapped, would require deep borings, from which 

 it must flow at the surface to be of material value for agricultural 

 purposes. Sites for .such boreholes must not be restricted in any 

 way, and must be placed in the position determined by a geologi- 

 cal sun-ey of the neighbourhood shewing the syncline in which the 

 water is stored, and the preceding and succeeding anticlines on 

 which the ends of the porous and impervious strata are generally 

 exposed by denudation, and alsO' the position of the axial bend, which 

 makes the folded rocks approximate tO' or fulfil all the conditions of 

 a basin. In like manner, if the high value of Avater for domestic 

 purposes makes it worth w-hile to pump it from a considerable depth, 

 a geological sun'ey must be made of the vicinity, and all available 

 knowledge relating to the water-bearing possibilities of the formation 

 should be collected, in order to ascertain if even a large expenditure- 

 would be likely tO' result in tapping a sufficient supply. 



THE "DOWSER." 



These considerations are, however, in the minds of some people,, 

 of no importance, and all that is necessar}- is to get a man called a 

 " dowser " or " water-finder,'"' whoi possesses some facult}- which enables 



