138 The Geology of the Gold Fields of British Guuma. 



This dyke divides near the cataracts into one of about one hundred feet 

 in Ijreadth, of medira texture, trending north and south, and into a 

 narrower one of far more compact texture striking north-north-east and 

 south-south-west. On the north side of the main fall at Caburi Rock, 

 the gneiss is traversed by a dyke of mica-diorite, by veins of a pink 

 granitite, and by others of a greyish epidote-granitite, whilst it is 

 intersected by narrow veins of pegmatite showing small grains and 

 patches of galena and of chalcopyrite. A little above the Caburi 

 Cataract a narrow elvan of epidote-augite-syenite strikes east and west 

 through the gneiss. 



The channel above Caburi Cataract runs between numerous small 

 islands until at Mora Rapids, about a mile from the head of the cataract, 

 numerous rounded masses of gneiss occur, which are similar in structure 

 to that at and below the cataracts, and are traversed by veins of an 

 intrusive micro-granite. The Mora Rapids extend at intervals for about 

 half a mile to the Little Mora Rapid, a7id to the rapids known as 

 Little and Big Haiowa, where, at the lower ones, the gneiss is inter- 

 sected by a narrow Ijelt of granitite succeeded by a broad expanse of 

 granitite-gneiss, which shows at the head of Big Haiowa Rapids a 

 somewhat obscure foliation. 



Above the Big Haiowa Rapids the chaiinels of the river wind 

 through the Makari Cataracts and Rapids. The cataracts are 

 in a belt of augite-syenite, which is intrusive through the gneiss, 

 and of which there are two varieties, a very coarse-textured, in part 

 porphyritic kind with, in places, large phenocrysts of colourless 

 orthoclase, up to one and a half inches in length, thickly scattered 

 through a white matrix with many brownish -yellow crystals of pyroxene 

 and here and there with tufts of small yellow crystals and a close- 

 textured, almost compact, rock of similar composition. The Makari 

 Rock, a huge isolated mass weathered in an extraordinary manner and 

 characterised by its ragged, jutting outlines, consists of the former 

 variety, and rests upon a bed of the latter, which, weathering with 

 rounded outlines, extends for about a quarter of a mile along the course 

 of the river. 



The Makari Rapids, which extend for a long distance, are over 

 granitite-gneiss, which is the prevalent rock along the river for 

 many miles, from hei'e to the Turesi Cataracts. Above Makari Rapids 

 the course of the river, although winding between islands, is fairly 

 free from rapids, the channels being termed by the boat-hands 

 " still-waters." Near the lower end of Koimara Hole, a channel com- 

 mencing al)out two and a half miles above the Makari Rapids, is a 

 narrow dyke of diabase (altered to proterobase) striking through the 

 gneiss from north-east to south-west. About a mile and a half from 

 this dyke, near the head of Koimara Hole, a belt of red granitite 

 intersects the gneiss for about four hundred yards. Its course is not 

 interrupted by rapids to any noticeable extent through the reaches a])ove 

 Koimara, but gneiss is well-seen at Haiowa Island, at some small rapids 

 a little above that island, and at Kusawe Island. Kusawe Cataract 

 and Rapids are caused by a narrow belt of granitite, some two 



