388 Report S.A.A. Advancement of Science. 



FLOWING WELLS. 



The principal yield of flowing water ha.s been from the Karroo 

 Beds, which have been subjected to more recent vf)lcanic movement, 

 and where dolerite has intruded into fissures formed in the sedimentary 

 crust with very little disturbance of the strata. These ridges of 

 igneous rock are quite impervious to water and extend to unknown 

 depths, so that they are practically underground dam-walls, cutting 

 off the flow of water along inclined strata of porous rock, and, where 

 these are covered by watertight beds and have also the strata im- 

 mediately below impermeable, the w^ater rises to the surface or above 

 it. In other parts of the countr)' also water flowing at the surface is 

 tapped, but the occurrence of the necessary conditions at shallow 

 depths is less frequent. However, there can be little doubt but that 

 great numbers of sites can be selected among the folded rocks of 

 the pre-Karroo formation where flowing water could be successfully 

 tapped by artesian wells at greater depths than tho.se reached up tO' 

 the present time. 



PUMtABLE WATER. 



With regard to water under ordinary conditions, standing in 

 saturated porous strata, moving slowly through them, or passing by 

 fissures, joints and cleavage planes into more ojjen channels or 

 subterranean reservoirs,' this in less or greater quantities exists every- 

 where in the Colony, except over some small areas of igneous rock. 

 in the Karr(K) Beds the strata are porous, the sandstones more so 

 than the shales, to a depth of 100 feet, and then become compact and 

 impervious. The Ecca Beds of the Central Karroo yield good supplies 

 at depths of 50 to 200 feet, and the Bokkeveld Beds of the Southern 

 Karroo at still greater depths, but the supplies tajjped toward the 

 coast line in the older rocks at these shallow depths are not so 

 plentiful as in the Karroo. In Bechuanaland, the relations of the- 

 water-bearing strata are not clearly understood, as the general 

 stmcture of the region has not l)een systematically examined, and 

 the boring done there, although in a measure successful, has been 

 executed without sufficient knowledge of the geological conditions, 

 while in the Transkeian Territories a sufficient number of boreholes 

 has not \et been put down to afford an idea of the volume and depth 

 of the supplies. .Since, however, the Ecca and KarroO' series are 

 developed there and the rainfall is far greater, there is every reason 

 to suppose that water will be found in larger quantities than in the 

 drier regions of the Karroo, although the igneous intrusions appear 

 at present to cause more trouble than those more to the West. 



QUALITY OF WATER. 



These underground waters are usually of excellent quality, though 

 occasionally they are impregnated with salts or sulphuretted hydrog'^n 



