Vol. 67.] WORCESTER, ROBERTSON, AND ASHTON (CAPE COLONY). 713 



the gorge near its mouth, and close to the base of the Table 

 Mountain Sandstone, there is a narrow band of different character. 

 This is considerably harder than the rest, and forms a con- 

 spicuous ridge in the middle of the field. This ridge is about 

 30 yards long and perhaps 15 feet high, and is composed of thick 

 slabs of rock with their bedding (or schistosity) dipping steeply 

 southwards. This rock weathers in a peculiar manner, forming 

 smooth rounded surfaces with a high polish, and is locally known 

 as the Olifants Klip, or Elephant Hock. The same rock can also be 

 traced on the other side of the Coos River, just below the Table 

 Mountain Sandstone, and at this point it is highly disturbed. As 

 before mentioned (p. 707), what appears to be a much decomposed 

 representative of this band is to be seen in the Hex-River Pass ; 

 and this observation is of much importance, since, if this really is 

 the same band, an important clue is afforded as to the relation- 

 ship of the rocks of the Malmesbury Series at these two widely 

 separated points. According to this, the ottrelite-rock probably 

 forms a member of the lower division of the Malmesbury Series, 

 and it appears to lie to the north of the axis of the principal 

 anticlinal fold, as indicated in the section (fig. 1, p. 705). 



A small number of specimens of the prevalent rock of this 

 district were collected, and they were found to be for the most part 

 somewhat crushed and slickensided grits of moderate to fine 

 texture, consisting of angular and subangular fragments of quartz, 

 in a rather schistose ground-mass of white mica and minute grains 

 of quartz. The edges of the larger quartz-grains are usually more 

 or less corroded, and in some specimens the characteristic sutural 

 structure of a quartzite can be discerned. There is here evidence 

 of a high grade of dynamic metamorphism. These rocks do not 

 differ in any essential character from the grits in the Hex-River 

 section. 



A considerable number of slices was cut from the rocks of 

 Olifants Klip, but all of them showed very similar characters, and 

 they may all be included in one general description [9466-67]. 



The principal minerals of this rock are quartz, white mica, and 

 ottrelite. In most specimens the rock may be described as composed 

 of more or less rounded grains of quartz of obviously clastic origin, 

 sometimes compound grains or minute fragments of quartzite ; 

 along the planes of schistosity lie in great abundance flakes of white 

 mica, somewhat fibrous in character and often curved and contorted. 

 In some cases there is a development of strain-slip cleavage. Scat- 

 tered through this ground-mass, with a distinct tendency to aggre- 

 gate in certain bands, are a large number of crystals of ottrelite, 

 measuring up to 1 millimetre in diameter. They usually are 

 roughly hexagonal or rounded plates, thin in proportion to their 

 diameter, so that sections normal to the basal plane show a 

 prismatic form. The edges of the crystals are very irregular, and 

 consequently prismatic sections never show any termination, but 

 are rather fringed at the ends. 



The colour of the crystals is to the naked eye very dark blue or 



