part 2] GEOLOGY OF THE MABBLE DELTA. 12.'* 



to the east, which, where it crosses the road, is associated with a 

 dark-l>anded rock composed of diopside, calcite, and olivine, the 

 last-named mineral being altered to a mixture of serpentine and 

 talc. 



Then' are a few other patches of marble towards the north : 

 namely, two on ( 'lurry willingham Park and one on the road- 

 cutting nearly 2^ miles north-west of the Mehlomnyama police- 

 camp. 



Almost 25 miles in a direct line up the ravine of the Umzimkulu 

 River is another strip of dolomitic marble 1 flanked and invaded 

 "by gneiss, and of interest because, among the types present, 

 are some composed of chondrodite and calcite like those which 

 will be described below. 



III. The Gkamte a>\l> Gneiss. 



The plutonic rocks surrounding the Port Shepstone marbles 

 are orthogneisses or gneissose granites, generally coarse-grained 

 varieties with large porphyritic crystals of felspar, white or pink, 

 sometimes deep red ; the ferromagnesian mineral is biotite, less 

 commonly hornblende. There are also streaks and belts of horn- 

 blendic gneisses, schists, and granulites, and it seems more than a 

 coincidence that these rocks should so commonly be found along 

 or close to the contacts with the marbles : for example, on Glen- 

 dale, in the south-western corner of The Glen ; on F.A. Xo. 1, 

 Bavaria, and the northern end of Lot 21. 



Such evidence as is available from this district, backed up by 

 some from the Zululand border, leads one to infer that these 

 basic rocks are intrusions in the dolomites that have subsequently 

 been recrystallized by the gneissoid granite. In the narrow strip 

 of folded leaden-grey impure marble, on the right bank of the 

 (Jmzimkuluwana just below the quarries, there are layers of horn- 

 blende-granulite that behave transgressively towards the bedding, 

 and must represent altered basic sills. These are doubtless the 

 rocks called * chlorite-schists ' by Draper. 



A very conspicuous feature of the gneiss around the marble area 

 within a distance of from 2 up to 6 or 8 miles is the presence of 

 red and brown garnet, and such types arc frequently accompanied 

 by pale aplitic varieties sometimes gneissose- — with an abundance 

 of this mineral: for example, on Glendale, The Tops, and near 

 the Umzimkulu Trigonometrical Station. Apart from this the 

 plutonic rocks are normal, the only exception noted being a variety 

 containing a pleochroic enstatite at Bomela Siding, (> miles south 

 of The Glen. 



Of the offshoots into the marbles the largest is one forming 

 a lobe running up the [Jmzimkuluwana almost to the northern 

 boundary of F.N. On its western side the contact must be nearly 

 vertical, but on the east it dips at a gentle angle below the marbles: 

 and some good sections along the left bank show that the intrusion 



1 Ann. Rep. Geol. Surv. S. Africa for 1913, p. 88. 



