RETENTION OF WATER, 



83 



the ground preventing a flowing off on any side, and the ortstein 

 preventing its sinking into the ground, they were frequently flooded, 

 and in this state they continued till the water was finally evaporated 

 by the summer heat ; and then things went to the other extreme, 

 namely, a drought, because the vapour of the subterranean water 

 could not pass through the stratum of ortstein. But here and 

 there, where the ortstein was awanting, or had been broken through, 

 places might be seen which were not so water drenched ; on these 

 grew wood very well, and showed that the barrenness was not 

 attributable to the composition of the superficial layers. 



The level of the subterranean water is about 3f feet below the 

 surface. Water for drinking brought from that level is yellowish in 

 colour, and harsh to the taste ; it is only when brought from a depth 

 of from 12 to 15 feet that the water begins to be drinkable. 



In the wet localities desci'ibed no oak can grow, for during the 

 season of spring the whole heat is required for the evaporation of 

 the water lodged there, and the oaks then expand their buds, and if 

 these retain vitality at all it is only in the end of May, when the 

 excess of moisture has disappeared, that they can burst forth, and 

 then the delicate buds are exposed to the summer heat, and they 

 succumb to the scorching sun of July. 



The maritime pine has also its buds ; and the period of its vege- 

 tation is also reduced by about two months by the stagnant waters ; 

 and by the ground ever passing through the alternation between exces- 

 sive drought and excessive moisture, this tree also suffers in its growth, 

 and on spots which do not become dry until the middle of summer 

 it does not grow at all. 



The importance of effects produced by the ortstein, of which men- 

 tion has previously been made, under its local designation, alios, calls 

 for some additional information being given in regard to it. 



In writing of the Water Supply in South Africa, I have had occa- 

 sion to refer to an impermeable layer in the sands of Namaqualand and 

 other districts operating as does the ortstein here. There travellers, 

 when driven to extremity for water, have found, on hollowing out a 

 basin in the sand, that at a little depth they reached a layer of other 

 matter ; and after a time, more or less protracted, water collected in 

 this basin, draining thither from and through the permeable sand, and 

 retained there by the impermeable stratum, often not thicker than a 

 penny, formed probably of clay, lime, and other matter washed down 

 from the superincumbent sand. It is impermeable to water ; 



