E. S. L. Schivarz — Hot Springs. 257 



I have always thought an explanation impossible, but accepting 

 the principle of isostacy, the whole matter appears simple and the 

 irregularities such as would necessarily be produced. For, regarding 

 the earth as a body that will respond to the smallest stress, provided 

 that it lasts long enough to make itself felt, we see a natural cause 

 for constant differential movement in the outer layers of the globe. 

 Eock is carried from the mountains and deposited in the sea as 

 sediment, ice weighs down the Poles, and even the waters of the 

 ocean in the ages seem to heap up at different places and produce 

 an additional weight on the crust. The differential movements 

 caused by this accommodation to varying stresses leads to the 

 formation of folds and faults; and while these are developing, some 

 of the motion is translated into a certain amount of heat. This has 

 been for many years our stock explanation of the origin of the heat 

 in the hot springs of the Colony, which occur for the larger part in 

 the folded mountain ranges, and I do not see any vital impediment 

 to pushing this principle somewhat further in order to explain 

 volcanic action as the result of earth-movements. 



In my recent survey of the Division of Willowmore I found 

 evidence of large movements which had affected the rocks near the 

 surface of the ground. The movement was a tearing one in two 

 directions, north and south, and east and west, and followed certain 

 lines which were separated by a considerable distance ; where the 

 two sets crossed each other some very wonderful effects were pro- 

 duced, the most remarkable being the brecciation of enormous 

 masses of quartzite belonging to the Table Mountain Series. In 

 one instance, at Land Kraal, in Baviaan's Kloof, there was in sight 

 a mass of this crush-breccia a cubic mile in extent, but how much 

 more of it was underground it was impossible to estimate. The 

 rock was in places coarsely brecciated, in others ground to fine 

 rock-powder like pounded glass ; it was either quite loose and 

 friable, or cemented together with silica or iron compounds.^ One 

 cubic inch of such a rock in the fresh state requires a load of 

 twenty tons to crush it up, but I am utterly unable to form an idea 

 of the force requisite to crush up even the amount that one could see 

 and measure at Land Kraal ; it must have been stupendous. This 

 case is very much more wonderful than any amount of contortion, 

 because the latter is aided by solution, and a very moderate tem- 

 perature and pressure will suffice to bend up the most resistant 

 rock, provided that it is allowed to remain under their influence 

 for a sufficient length of time. Had this enormous force been 

 concentrated over a less extensive area, and had the rock contained 

 a flux or been composed of a less resistant material than quartzite, 

 there is little doubt that the brecciation would have been converted 

 into fusion and a volcano would have been formed. The distribution 

 of the volcanoes, too, under this mode of origin would have closely 

 imitated that which we find in some actual volcanic areas, the 



' These crush-breccias will be described in the forthcoming Annual Report of th& 

 Geological Commission, Cape Town, 1904. 



DECADE v. — VOL. I. NO. TI. 17 



