92 THE BLINK KLIP BRECCIA 



The fragments are invariably angular, and they are, 

 without exception, rocks of a type usually found near 

 the base of the Griqua Town series. The only change 

 they seem to have undergone is due to enrichment in 

 iron oxides. 



The hills made of the breccia are dark red, often 

 almost black in colour, and have steep, rugged sides. 

 One of the smaller hills, Kopje Alleen, is shown in Plate 

 II. ; it is rather less than 100 feet high and rises from 

 the Campbell Kand limestone which is exposed on the 

 surrounding flat ground. 



Where the Blink Klip breccia is absent the banded 

 and magnetic cherty rocks form the lower 2,000 feet or 

 so of the series. They are for the most part thin bedded, 

 the individual layers are rarely more than half an inch 

 thick. Silica in the form of chert, seen under a high 

 power of the microscope to consist of minute interlock- 

 ing areas of quartz, forms the base of at least a great 

 part of these rocks, but with the silica there occur red 

 and yellow hydrated oxides of iron in minute particles 

 and magnetite in rather large grains, often with octahe- 

 dral faces. Traces of carbonates, either irregularly dis- 

 tributed in short layers or scattered through the rock in 

 small rhombohedral crystals, in which the carbonate is 

 often partly or wholly replaced by chert, are frequently 

 seen. The magnetite is very much more abundant in 

 some layers than in others, and these evidently represent 

 originally richly ferruginous layers. 



Perhaps the most remarkable feature in this singular 

 group of rocks is the widespread occurrence in them of 

 the soda-amphibole, crocidolite. Crocidolite is a blue 



