120 Transactions of the South African Philosophical Society. 
The plates accompanying this paper afford, we hope, sufficient 
evidence of the real nature of the striae and hummocks, and will 
prevent any reference of the phenomena to subsequent move- 
ment of the rock-masses and resulting slickensiding. The low 
angles at which the striae are inclined, and the absence of 
evidence of any considerable movement or disturbance in the con- 
glomerate and horizontally overlying shales are alone sufficient to 
put such an explanation out of court: for many of the surfaces are 
inclined at an angle of less than 20°, and some are horizontal. From 
the nature of the case it is extremely improbable that the rocks have 
been so displaced as to bring highly inclined fault surfaces into a 
nearly horizontal position, so if these are slickensides the forces 
which gave rise to the faults must have been tangential thrusts of 
considerable magnitude, but it is impossible to admit that soft rocks 
of the nature of the conglomerate and shale of the moe have been 
subjected to any disturbance of this sort. 
It is sometimes suggested that the abrading action of wind-borne 
sand will account for such surfaces as we have described, but our 
experiences of sand-worn rocks does not at all bear out the sugges- 
tion. Wind-borne sand polishes rocks and eats out the softer parts 
more rapidly than the harder, whether these are in patches, as in 
granite, or in lamin, as in some of the Doorn Berg rocks, but long, 
clearly marked scratches, sometimes 45 inch deep, such as we are 
dealing with, are not, in our experience, produced in this way. 
Sand-worn rocks are frequently met with in the Colony, but are 
easily distinguishable from glaciated ones by any one who has seen 
both. 
The appearances seen in the three localities, Jackal’s Water, Klein 
Modder Fontein and Vilet’s Kuil, at considerable distances apart, 
can be satisfactorily explained only on the supposition that the 
country was traversed by land-ice; and the presence of the till-like 
variety of the conglomerate in the same district, probably about 
the same localities, confirms that explanation. Unfortunately, as 
we mentioned before, the exact nature of the conglomerate at the 
three localities is unknown, that is, whether it is a true till or 
whether it is a stratified rock with glaciated pebbles. We only know 
that the rock contains numerous scratched pebbles and boulders ; 
but this is a small point and does not affect the confirmation. It is 
evident that the country was depressed under water after the forma- 
tion of the till of Prieska, and it is quite possible that sedimentary 
rocks were deposited on a floor consisting partly of till and partly of 
the floor from which the soft till had been removed, or on which no 
accumulation had taken place. 
