186 



which holds many thousand millions of gallons of water, fairly extensive 

 irrigation has been practised for several years. Under this treatment the 

 barren area has gradually spread, and at present the nearest land that is 

 being cultivated below the darn is no less than seven miles distant there- 

 from. It is, nevertheless, 'estimated that about 20,000 acres of irrigable 

 land of good quality are still free from any signs of alkalinity, and avail- 

 able for cultivation. 



Two samples of water from artesian borings in the vicinity of the dam 

 were analysed with the following results, stated in grains per gallon : 



No. 1. No. 2. 



Sodium chloride 48'94 358'98 



Magnesium sulphate 49'20 177'57 



Calcium sulphate 53'26 76*86 



Calcium carbonate 10' 16 147'95 



A specimen of water from the dam itself was found to contain chlorine 

 in combination as chlorides to the amount of 1,1 54 '6 grains per gallon, 

 and, on another occasion, a sample similarly taken yielded the following 

 figures : 



Sodium chloride 862'9 grains per gallon. 



Sodium sulphate 226'3 



At some places in the neighbourhood, beds of limestone, containing 

 gypsum, occur; specimens of these were analysed, but did not prove of 

 good quality. 



The land most affected by alkaline salts is that in the immediate 

 proximity of the dam, and from there the saline area is working its way 

 downwards by degrees, the lands being drenched with water during the 

 season, and then left to the action of evaporation, which does not fail to 

 draw the salts to the surface, with the consequence that, in the long run, 

 one tract of land after another has been discarded as too salt for cultiva- 

 tion. Under such circumstances, the practice has been to transfer to a 

 plot of virgin soil, until that, too, in turn, becomes too alkaline for use. 



To test chemically the results that this mode of cultivation brings 

 about, samples of soil, T and V, were taken, respectively, from Lot 111, 

 which had been under cultivation for seventeen years, and had, during that 

 period, grown fourteen crops of wheat, and from Lot 94, which had never 

 been cultivated, at a spot 315 yards from that where T was collected. The 

 crops at T were originally as good as could be desired, but have been 

 gradually deteriorating. The sample taken at V is typical of the Van 

 Wyks Vlei soil in its natural state. 



The way in which these samples were collected was as follows: In 

 each case an excavation was made to a depth of seven feet, and, down one 

 side of the excavation, a vertical groove, of six inches square section, was 

 cut by removing for analysis blocks of soil of six inches cube at six-inch 

 intervals. The first sample of each series was taken from the surface to 

 a depth of six inches, and then samples of each alternate six inches below 

 that. In both cases, at a depth of six feet a stratum consisting for the 

 most part of large-sized stones was encountered; of this it was not con- 



