140 Trmisactions of the Boyal Society of South Africa. 
brack, and although the gypsum in these layers may minimise to some 
extent the evil effects of the black brack by converting it into sodium 
sulphate, it is not probable that it will do away with these effects entirely. 
There is a general resemblance between the soils K and M, the former 
being an improvement on the latter. The worst kind of brack, sodium 
carbonate or black brack, occurs in the soils L, N, and P. At L it makes 
its appearance at the fourth foot, at N it rises to the third, and in larger 
proportions, while at P it appears at the surface, and is distributed 
through the soil profile in amounts averaging from two to three times 
those in the corresponding soil layers at N. 
It will be noticed that the magnesium salts exceed, on the whole, the 
lime salts in quantity, and I may here say — what does not appear from 
the figures already given — that the soils K and M show a small propor- 
tion of the rather undesirable magnesium chloride in the first couple 
of feet. 
The amounts of alkaline carbonates in the Thebus samples are lower 
than in the soils of the Tulare Experiment Station, California, as reported 
by Professor Hilgard, and the alkaline salt present in largest proportion 
is sodium sulphate at K, and sodium chloride at the other points where 
samples were taken ; but then the Californian Station may be taken as 
representing an extreme case, and there is no saying whether much 
worse instances than the present may not be found at Thebus if a more 
complete investigation be undertaken. 
It will be noticed how irregularly the soluble salts are distributed 
through the soil ; this irregularity is caused by the varying permeability 
of the soil layers, and by the bands of gypsum which traverse the valley. 
This variability also showed itself in the peculiar nature of results obtained 
by ordinary agricultural chemical analysis from other samples collected 
at Thebus. These samples were evidently not typical, and may even, in 
some cases, have been taken out of the very bands of gypsum just men- 
tioned, hence they showed abnormal percentages of lime. Irregularities 
of this type are of common occurrence in alkali soils ; King (" Irrigation 
and Drainage," p. 283) states that " in examining soil for alkalies it is a 
matter of the utmost importance to recognise that the distribution of them 
is extremely liable to be capricious, and that it is easy to overlook their 
presence by stopping the sampling of the soil just short of the level at 
which all the alkalies had chanced to be concentrated ; or, again, by 
taking a sample of the first, second, and fourth feet, or of the first, third, 
and fourth feet, when, owing to the capricious distribution, all of the salts 
had been collected in the second and third foot, and thus were overlooked 
because it may have been thought not worth while to make a complete 
section of the soil in question." 
An analysis was made of a sample of efflorescence from the soil in the 
