DOLERITES AND EHYOLITES OF NATAL AND ZULULAND. 147 



Zululand, is doubtless a junction specimen of the enstatite 

 dolerite (426), described later on p. 148. 



NoRiTES, Pyroxenites, and Enstatite-Dolerites. 



The igneous rocks, of "granitic type," as desci'ibed by 

 Anderson,^ which form the Umqueme Range, and are stated 

 to be older than the Table Mountain sandstone, are mainly 

 norites or coarse-grained enstatite-dolerites. From their 

 mineral character they might very well be more deeply seated 

 rocks derived from the same magma which supplied the 

 dolerites just described. They occur about three or four 

 miles north of Dingatuli Hill, between the Hlabisa and 

 Lebombo Magistracies. They vary from dark pyroxenites 

 (81 and 85), consisting almost entirely of a slightly pleochroic 

 enstatite with very little felspar, to colourless granite-like 

 rocks (84, 8Q, 87, 411, 414) allied to anorthosites, since they 

 consist mainly of felspar (labradorite with symmetrical 

 extinctions of 22^-27°) with very sparingly distributed crystals 

 of pale brown enstatite. Iron ores in these particular extremes 

 are almost entirely absent. Of intermediate character is a 

 coarse-grained olivine enstatite dolerite, or olivine norite from 

 the eastern end of the Umqueme Range (408). This is a 

 dark brown gabbro-like rock, in which the enstatite and 

 olivine are in excess of the felspar. The enstatite is in large 

 crystals showing traces of prism faces, and depolarising only 

 in grey tints. It is of later growth than the felspars, since it 

 encloses or is penetrated by the latter in sub-ophitic fashion. 

 Associated with the enstatite is a more strongly refractive 

 augite, which in thin slices under the microscope is seen in 

 broad, irregulai-, ophitic plates, sometimes penetrated by 

 tongues of enstatite from an adjacent crystal, or enclosing 

 small fragments of enstatite in optic continuity with an 

 adjacent crystal (see PI. V, fig. 1). This structure is some- 

 what similar to that exhibited by intergrowths of hypersthene 



' See ' Second Report," p. 66, and • Third Report," p. 133. 



