Soils of the South-Western Districts of the Cape Colony. 1438 
influence of the underlying limestone. A diagram (see Plate X VIII.) 
enables us to grasp the continuous diminution of lime at a glance. 
About Hopefield:-and to the north-west of it there is again an 
increase of lime in the soil, clearly traceable to the compacted sand 
dunes previously referred to. In some cases—samples 99 and 102 
for instance—the amount of lime is very large proportionately to the 
other constituents of the soil, for here, on the clay slate, the 
simultaneous increase of potash is not so noticeable as, for instance, 
in soils 25 and 29 where the underlying rock is granite. 
Diverse from the changes in the lime content of the soil, strangely 
enough, is a marked increase in the phosphoric oxide as one travels 
northwards from Durban. Taking the clay slate soils of the Cape 
and Malmesbury Divisions as a whole one may conveniently divide 
them into three sections as regards the amount of phosphates the 
soil contains. First of all may be taken the area south of the farm 
‘‘Uitkyk”’ in the Koeberg district, then the stretch of country 
between ‘“‘ Uitkyk” and the Great Berg River, expressly excluding 
the Zwartland soils, and finally the area covered by the Zwartland 
Field-Cornetcy. The first of these three areas comprises samples 40 
to 58—19 in all; they average ‘029 per cent. of phosphoric oxide. 
The samples taken from the next area are 34 in number, comprised 
in two sets, namely Nos. 59 to. 76 and 92 to 107. In these the 
-average percentage of phosphoric oxide is respectively 041 and 
‘046: the former represents the country north, and the latter that 
south of Zwartland. The Zwartland area comprises the 15 samples 
77 to 91, and they yield an average of -058. 
There is a diminution of potash, somewhat similar to that 
already noticed in the case of the lime, as we proceed from south to 
north within the area under consideration, but in this case it is not 
as striking nor as regular. Several of the southernmost soils contain 
a respectable proportion of potash—for instance, Nos. 41, 45, 49, 51, 
and 54, the percentage of potash in which averages °32: these soils 
may all be said to berich in potash. In the Zwartland area there is a 
noticeable difference in respect of potash between the western soils 
and eastern soils ; the former, comprising Nos. 77 to 84, contain on 
an average "102 per cent., the minimum being -077, whereas the 
samples taken from the more easterly part of the Field- Cornetey, Nos. 
85 to 91 yield an average of only -060 including a minimum of -020. 
Summarising our results with respect to the clay soils of the Cape 
and Malmesbury districts we may say that no less than 16 out of 
the 68 soils examined were poor in all three of the essential inorganic 
elements of plant food; there is one such poverty-stricken patch 
about the middle of the Koeberg district, represented by samples: 50, 
