414 ME. W. GIBSON ON THE GEOLOGY OF THE GOLD-BEAEING 



has been exerted both on the conglomerates and on the adjacent 

 rocks. This band is about 45 feet thick, the quartzites (a) on either 

 side of it being the most highly metamorphosed of any in the mine. 

 It seems clear that this band (d) marks the place and the direction 

 in which the rocks have yielded most to pressure. The resulting 

 schist is probably chloritic. 



The dip of the reefs in the Henry Nourse Mine is nearly 90°. 

 In the deep level another conglomerate has been struck by a diamond 

 drill at a depth so slight as to lead to one of two suppositions : 

 either the dip of the reefs has decreased very rapidly, or the reef 

 passed through by the diamond drill is one of those in the cross-cut 

 north of the main shaft repeated hy faulting. 



The sections in the Salisbury and Henry Nourse Mines, described 

 above, undoubtedly prove that the strata have been considerably 

 disturbed, crushed, and metamorphosed. The succeeding descrip- 

 tions of the Main Reef Series, as it is developed in the mines east 

 and west of the typical locality along the line of strike, will show 

 to how small an extent the strata vary in their original lithological 

 character, and how widespread is such metamorphism as has 

 aifected them. 



(b) The Main Reef Series west of the Salisbury Mine. 



In the Eobinson Mine, which lies about a mile west of the 

 Salisbury, the Main Reef and the Main Reef Leader have approached 

 until they come close together, the surfaces on either side of the 

 divisional plane being smooth, and suggesting that the quartzite has 

 been nipped out. There are thus in this mine only three reefs — a 

 North Reef, a very thick Middle Reef, and a South Reef. The 

 lower levels alone reveal the true nature of the strata. The schist- 

 like character of the cementing-material is very apparent, portions 

 of it exactly similar to true silvery mica-schist being common. The 

 dip of the three reefs varies from 45° to 50° S., the change from 

 that observed in the Salisbury Mine coming in west of the spruit 

 which divides the Robinson property into two parts. 



In the Langlaate Estate Mine, situated still farther west, we 

 find a band 10 feet thick, lying to the north, called the Main Reef, 

 another 5 feet thick (to the south) called the South Reef, and a 

 very inconstant middle reef which may be the Leader. The true 

 North Reef, if it exists at all, has not been reached. 



In the Croesus and other mines west of the Langlaate only two 

 reefs, thinner than those described, are found, called respectively the 

 Main Reef and the South Reef. The dip is 30° S. The South Reef 

 is very variable, seldom exceeding 2 feet in thickness, while in many 

 places it disappears altogether. 



In the Durban Roodeport and Princess Mines this reef is some- 

 times represented by a single line of pebbles, while in other parts 

 of the mines it thickens out. The rocks in both mines are highly 

 cross-faulted. The composition of these reefs is almost identical 

 with that of the reefs in the Salisbury Mine. 



