50fi PROFESSOR J. W. GREGORY. 



granite bosses and tors. The rock is exposed in many railway cuttings, and the soil 

 is all a granitic wash. The most widespread variety is a massive biotite-granite. 

 The granite in places is coarsely porphyritic. 



After passing across the second plateau (the Cretaceous being the first), the 

 railway at km. 72h begins the ascent on to the third plateau. The level of 2972 feet 

 is reached at the Portella Coroteva at km. 95. Occasional exposures of gneissoid 

 rocks occur, as at the cuttings at km. 77 and km. 90. Portella Coroteva cuts 

 through a ridge of granitoid biotite-gneiss, intersected by numerous pegmatite 

 veins, and interbedded with some biotite-schist. The numerous tors included in 

 the magnificent view from the Portella Coroteva shows that the granite extends 

 far on both sides of the railway and eastward over the basin of the Catengue to the 

 hills around Cubal. 



The railway descends this ridge, passing massive porphyritic granite at km. 104^ 

 and also at km. 112. The granite is intruded by occasional altered basic dykes, as 

 at km. 108 and Portella Solo. At km. 114 the granite is light gray and porphyritic 

 and is associated with decomposed biotite-schist or biotite-gneiss traversed by many 

 quartz veins. 



Large exposures of foliated white granite occur at Catengue, km. 121, and the 

 brown soft decomposed biotite-gneiss reappears at km. 124 ; and it is here broken by 

 bosses of white granite weathering in large exfoliation surfaces. From Catengue the 

 railway rises to the Portella Solo, km. 134-|, 2972 feet. At this pass the granite is in 

 contact with a compact selvage of hornfels, which Mr Tyrrell has determined as a 

 recrystallised basalt hornfels or augitite. One and a quarter km. to the east of the 

 pass the granite becomes more basic ; at km. 143 the rock beside the line is a white 

 granite, which probably forms the picturesque tors to the north and the larger 

 granite hills to the south. Near Bombola, at km. 157, is another occurrence 

 of compact hornfels. Thence to the Cubal River (station at km. 197, 2976 feet) 

 the line continues through granitic country between numerous rugged and 

 picturesque tors. 



On the return journey Professor Martin followed the course of the Cubal for 

 some miles to the north, and found that the ordinary granites extend along the 

 river and are intruded by dykes of augitite or basic basalt similar to that of the 

 Portella Solo. 



Before reaching Cubal the general condition of the country improves owing to 

 increasing rainfall. After crossing the Cubal River there is a long level tract with 

 no rocks exposed beside the line ; and the improvement in the condition of the 

 country is shown by the large baobab at km. 205^, being the last beside the line. 



The granite continues for km. 70 east of the Cubal, and it rises in high tors and 

 bosses. The granite at km. 238 is hornblcndic ; but most of the specimens examined 

 consist of the ordinary gray biotite-granite, though some is more basic and there are 

 occasional exposures of granodiorites, 



