NOTES ON THE GEOLOGY AND MINERALOGY OF NATAL. 



By J. A/ H. ArmstroxGjF.C.S. 



• As is already well known, there exists within the limits of the 

 Colony of Natal a narrow belt of granite, gneiss and schistose rocks — 

 extending from the Mapamulo District, in the northern part of 

 the Colony, to near the mouth of the Umtamvuna River in the south. 

 The Table Mountain Sandstone Series rests unconformably on these 

 older rocks. The name Palaeozoic Sandstones has been adopted by 

 some, but a study of the series, in the various Colonies in which they 

 occur, cannot alter the fact, I think, that these sandstones, in being 

 designated Table Mountain Sandstones, possess their right title both 

 in name and correlation. The other rocks then belong to the 

 Archaean System, and are known as the Swazieland Series and 

 Intrusive Granite. To a study of these a great part of my time 

 has been devoted for some time past. At various localities, through- 

 out this narrow belt, the soil and subsoil found covering these 

 ancient rocks is of comparatively no depth. At times it is to be seen 

 not more than a few inches deep. This fact no doubt accounts for 

 the absence of bush and forest from large tracts of land on the belt. 

 The country is very broken and at times rugged. The pictiu'esque- 

 ness of the scene is often enriched by the occurrence of an outlier 

 of the Table Mountain Sandstone Series resting on these older rocks 

 and forming a flat-top})ed hill. The proportion of subsoil to the soil 

 is often infinitesimally small and at the junction of the subsoil and 

 rocks there can be seen occasionally the sites of the ancient courses 

 taken by surface waters in their flow to lower levels. The granites 

 for the most part consist of aggregates of quartz, felspar and mica. 

 The quartz is usually of a clear glassy nature, though I have seen 

 pieces of it exhibiting at times a bluish or reddish tinge. The felspar 

 is usually the flesh-coloured variety of orthoclase though triclinic 

 felspar is also to be found. The mica grouj:* is rejiresented by either 

 or both Biotite and Muscovite, but the latter variety of mica I have 

 come across usually in the more coarsely crystalline varieties of 

 white coloured granite. 



One cannot help being struck at the variability in colour that 

 occurs in the felspar in the granite within certain areas. In some 

 specimens, within a distance of but a few inches, I have seen the 

 colour of the felspar vary from a light reddish brown to almost pure 

 white. In fact in some places the granite has its felspar constituent 

 so white that, were it not for the similarity in mineralogical com- 

 position, and the variability in colour of the felspar, one would be 

 apt, at a first glance, to subdivide them, and to assign them to, 

 separate ages. 



These granite rocks can be well examined along the beds and banks 

 of streams where their outcrops are often visible. Overlying them 

 are to be found true gneissic rocks. These likewise differ in the 

 colour of the felspar constituent present, but the remarks applicable 

 to that mineral in the case of the granites are equally applicable 



