176 Transactions of the Boyal Society of South Africa, 
It is for these reasons that the close-grained Lower Beaufort Beds 
yield supphes which in many places seem extravagantly in excess of what 
would be expected from the closeness in grain of the individual beds. It 
follows that the supplies to be obtained from such formations will be 
drawn principally from the surface zones within which fissures and joints 
exist, and deep borings will generally not be more advantageous. 
The results of boring in the Karroo entirely support these contentions, 
for it must be noted that the numerous dolerite intrusions cutting through 
the strata cause the shallow ground-waters to become concentrated at 
certain points and thus enable wells to be sunk at such spots with 
success. 
Permeability of Strata. 
It is very unfortunate that all the experiments upon the permeability 
of sandstones have been carried out upon varieties possessing a porosity 
of over 15 %, usually a much higher value. The rate of flow of water 
under pressure through such weakly permeable sandstones as those of the 
Beaufort Beds of the Cape Province is therefore quite uncertain, though, 
from the rapid falling off of permeability with diminution of porosity as 
shown in other more open-grained sandstones, the figures would appear to 
be very low for the formation in question. 
As regards the Transvaal, the figures given in the table apply to 
material from quarries only, and it is likely, judging from analogy with 
the data available from the Cape, that the porosity in depth of the Coal 
Measure grits and sandstones will range most probably from about 5 % 
to 12 %. 
Experiments like those carried out by Baldwin-Wiseman * upon the 
rate of flow of water under varying pressures through unweathered blocks 
of such sandstones, are much to be desired, because in the Transvaal 
these rocks in a number of places occupy gentle depressions in the older 
impervious formations, they are invaded by dolerite to a limited degree 
only, and they crop out in regions of fairly good rainfall. 
The question of the permeability of these sandstones is therefore an 
important one in view of possible deep boring in certain localities. It is 
to be hoped that in the near future determinations may be made of the 
permeability of the sandstones of the Karroo System, a representative 
set being selected which will cover the wide range in porosity possessed 
by the various types as brought out in the following tables. 
With such data secured, many problems of underground water supply 
could then be attacked with more hope of success. Upon the results 
obtained the policy of deep boring would perforce be based, while the 
ideas of boring engineers upon this subject would necessarily become less 
nebulous, and the scope of their operations more extended. 
* Min. and Proc. Inst. Civil Engineers, vol clxv., part 3, 1906. 
