Professor E. H. L. Schwarz—The Tygerberg Anticline. 489 
anticlinorium and an anticline. And whereas on the Alps the 
prodigious force has crumpled a whole succession of formations and 
has allowed recumbent folds to develop, in the coast ranges of the 
Cape there has been only a single formation folded into the main 
range, and where an overfold has taken place it is of restricted extent. 
All the subsidiary folds that develop on the inner or ‘stoss’ side of 
our ranges are upright folds, and I wish to lay stress on this point 
because the large number of papers recently written on recumbent 
folds in and around the Alps has directed attention to this peculiar 
feature. Dr. C. Sandberg has ascribed such an origin for the abrupt 
range of quartzites that rise from the plains north of Prince Albert," 
in spite of the photograph illustrating the nature of the range which 
Mr. Rogers published in his ‘‘ Geology of Cape Colony,” p. 141. In the 
accompanying photograph (Plate XXII) I show the eastern end of the 
Tygerberg, as this sharp crest is called, where the bare dip-slopes of 
quartzite are seen rising from out of the plain, composed of Dwyka 
conglomerate, almost as if they had been made of sheets of some 
pliable metal like zinc. There are features of interest enough in the 
Tygerberg without suggesting the additional one of recumbent folds, 
and however much I should like, for the sake of the interest which 
such a structure would evoke, that Dr. Sandberg was right, yet if 
the structure of the coast ranges of Cape Colony is misunderstood, 
much of the geology of South Africa would become unintelligible. 
The difficulty which the Tygerberg presents is that although the 
quartzites tower up in a narrow vertical anticline, the wyka shales 
and conglomerate around it are only moderately inclined, and indeed 
in some places lie actually flat. The Dwyka conglomerate is an 
exceedingly tough, close-grained rock, being in fact a glacial till that 
has been compressed and hardened by the pressure of some thousands 
of feet of superincumbent strata now removed by denudation. The 
Witteberg Beds, on the other hand, show in the extraordinary twists 
and bends that nearly everywhere characterise the series, that the 
rock was mobile when deeply buried; the rocks that form the chief 
bulk of the strata are fine-grained quartzites, and I ascribe this 
mobility to the fact that silica at temperatures and pressures found in 
the earth’s crust at a depth of a couple of miles is easily soluble. 
What has happened, then, in the Tygerberg, is that an earth-fold has 
developed with an east and west trend; the Dwyka conglomerate has 
yielded but slightly to the folding, but the underlying quartzites were 
reduced to such a state that they were ready to flow in any direction 
where there was relief of pressure, the process being one of solution 
and redeposition of the substance of the individual grains. Eventually 
the folding became so great that the Dwyka conglomerate had to 
yield, but instead of bending, a vast rent developed through the strata 
down to the underlying quartzites. This gave relief of pressure, and 
the quartzites came squeezing through the gap in the overlying beds 
much in the same manner that lead may be made to flow between the 
jaws of a vice. The process in the case of the Tygerberg was 
1 Trans. Geol. Soc. South Africa, vol. ix (1906), p. 82; Nature, August 22nd, 
1907, p. 423. 
