Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/153

 It is only visible at the lowest parts of the river-valleys and near the coast, in fact wherever the river, by its erosive action, has removed the sedimentary rocks. If we draw a straight line from the Umtwalume river due north, we shall touch all those parts of the country where granite and gneiss reach the surface through the covering of stratified rocks. Granite, as Livingstone correctly observes, forms the bones of the country, which at places are seen through the skin. It only forms hills and the bottoms of river- valleys. The granite is mostly a fine-grained grey variety ; sometimes it becomes very coarse and contains large crystals of feldspar ; altogether it has the same appearance as the granite at the Cape, which Hochstetter first described as similar to the Karlsbad granite. At some places there is a red variety, in which the quartz and mica nearly disappear, being a mere feldspathic rock, in which decomposition reaches a great depth, when it presents a kaolin-like appearance, similar to that found by me at the Umzinto and at the Jfafa river. Further to the south, at the Umtwalume, Ehlongeni, and Umkobe rivers in Alfredia, the belt of granite becomes broader, and represents a distinct zone. The greatest elevation is reached by the granite in the counties of Victoria and Umvoti, where the Noodsberg group of mountains and all the surrounding country, and the bottoms of the valleys of the rivers Umvoti and Tugela, in the latter very far up, consist principally of this rock. I have found gneiss at several places, as, for instance at the base of the Sluten-Konga (Mount of Mist), at the head-waters of the Umtwalume, &c. ; but nowhere was it practicable to map it, as the high grass vegetation rendered surveying quite impossible. The granite is traversed in all directions by quartz-veins, which seldom have a thickness of more than from about 1 inch to 2 feet. The quartz itself is a beautiful white variety, almost like glass, which, besides occurring in veins, is very frequently met with in large masses, called " reefs," which usually very soon thin out towards their base. These quartz masses were always a subject of great interest in Natal, as it was thought that they would yield gold in paying quantities. Such is actually the case at almost all places, but not in sufficient quantities to yield a profit for crushing it. At the Umzinto-river valley, after a long time occupied in searching, I succeeded in finding small traces of gold in a variety of grey granite, which also reminds one much of the granitite of Bohemia. The alluvium there also contained gold, but only in traces, and not nearly sufficient to pay any one to work at it.

2. Mica-schists, Clay-, Chlorite-, and Talcose Slate formations. — All these slate formations are to be met with at places where the granite base is laid bare ; and everywhere the slates stand nearly upright, at an angle of 70-75°, with a strike from north to south. The clay- and talcose slates are very well seen at the Umzimculuana (little Umzimculu), in the county of Alfred, and at the Tugela, at the junction of this with the Umziniaty river, and also at the Itemani, a small tributary of the Tugela. At the Umpampinioni river a dark grey clay-slate, dipping at an angle of about 40° and striking from south to north, possesses considerable thickness (about 200 feet or more). It rests on granite, and underlies and is conformable