Minutes of Proceedings. xiii 



percolates below the sand in the beds of the rivers, and can be 

 recovered by making shallow pits. 



Water accumulating in the soil tends to move towards lower levels 

 and is influenced by topographical features, dykes, fissures, &c. 

 Pans and patches of soil, covered by calcareous tufa, are first-rate 

 places at which to sink wells. The underlying formation is important 

 in connection with underground storage. 



Granite and gneiss are uncertain rocks in which to sink, though 

 sometimes they afford excellent supplies. The diabase comes next 

 in water-bearing capacity, but the dolomite formation of the Kaap 

 Plateau is certainly the finest water carrier. 



Of the other factors upon which the accumulation of water 

 depends, the most important is the rainfall. This varies from 15 

 to 26 inches, and takes place in the summer months ; practically 

 none of the water reaches the sea directly. 



The proportion absorbed depends upon the porosity of the soil 

 and the duration of the periods of rainfall ; the losses are caused by 

 evaporation from the surface and through capillary action, and owing 

 to transpiration by plants. 



In years of ordinary rainfall the additions to the soil must just 

 balance the quantities lost, and it is only when the rainfall is 

 abnormal that the level of the ground water is permanently raised. 

 When artificial openings are made the soil experiences a certain loss 

 which may not be made good afterwards, and the wells have to be 

 deepened until they attain their limiting depth. Boreholes can 

 be used to drain the greater depths, but no advantage will be gained 

 by going down more than a few hundred feet. 



There are no localities where large artesian supplies can be readily 

 obtained. In some of the valleys subsurface dams can be adopted 

 successfully. For ordinary requirements there is plenty of water 

 at the present time, but care should be taken that too great a drain 

 is not made upon the natural resources of the country. 



A paper by Dr. Thos. Muie, " A Set of Linear Equations connected 

 with Homofocal Surfaces," was read. 



Ordinary Monthly Meeting. 



March 28, 1906. 



Dr. J. C. Beattie, President, in the Chair. 



Mr. E. T. Mellor was nominated as an Ordinary Member by 

 Messrs. A. W. Eogers and A. L. du Toit. 



33 



