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SCIENCE PROGRESS 



whether they melted out a passage for themselves, or simply 

 occupied pre-existing fissures, is a problem with which we 

 are not concerned here. The folded mountain ranges of the 

 coast are a sufficient effect. Between the folded mountains 

 and the escarpment, where the dolerite sills begin, there is a 

 denuded area showing occasional flexures, but on the whole 

 consisting of nearly horizontal shales and sandstones traversed 

 by quartz veins. This last feature seems important, for it 

 shows that, while the disturbance of the dolerite intrusion was 

 being transmitted to the outer edge of the Neo-afric region, 

 the intervening tract was so far from being in compression as 

 to be traversed by open fissures, which subsequently became 

 filled in with vein quartz. Curiously enough, this last feature 



Fig. 2. 



is faithfully reproduced in miniature in Mr. Mellard Reade's 

 sink, for, in the centre of the sheet of lead, there are a number 

 of transverse fissures, in this case gaping and empty. 



Such, in brief outline, is the character of the folding in the 

 south-western portion of South Africa ; the period during which it 

 was in progress was approximately in late Jurassic times. The 

 details are almost infinite in their variety, and of never-failing 

 interest to the geologist, but I will confine attention here to the 

 following types, which are of more general interest : (a) Folds 

 in which the beds fail to adhere in the angles, (b) folds in which 

 stronger beds have caused the weaker ones to flow at a greater 

 rate than themselves, and (c) folds which have, as it were, 

 tumbled on themselves, and have produced vertical pressure. 



The area from which I will take my illustrations is that of 



