CHAPTER XV. 



THE MAZARUNI RIVER. 



The first rocks seen on the right bank of the Mazaruni at Bartica 

 Point, near the junction of the two rivers, Essequibo and Mazaruni, 

 are of a light-grey, finegrained granitite-gneiss, traversed by a 

 broad belt of hornblende-schist, with frequently much contorted 

 foliation. The schist is intersected by many thin veins of quartz, 

 while in places it changes to a biotite-schist. The general trend of the 

 belt of hornblende-schist is south-south-east and north-north-west, and 

 frequent exposures ot it and of the gneiss are seen on the right bank 

 of the Mazaruni to near a point below Susan Island nearly opposite 

 to the Penal Settlement. They are there succeeded by a broad belt 

 of gre}', medium to fine-grained granite with a somewhat gneissose 

 character. This extends for a distance of about nine miles alono- the 

 course of the river to the small rapids at Tutruba, and to near the 

 southern end of Karia Island. The granite is exposed on several 

 islands, and large and small rocks of it occur at intervals along the 

 river ; but its general character may be best seen in the quarries at 

 the Penal Settlement, in Ansdell's quarry at Palmer's Point, and along 

 the course of the Barakara Creek. It differs from the majority of the 

 granites of the colony by containing fairly plentiful large flakes 

 of original muscovite in addition to biotite mica. It is traversed by 

 many veins of fairly coarse-textured pegmatite, one of which exposed 

 near Kartabo Point, at the junction of the Mazaruni and Cuyuni 

 Rivers, has the structure of a well-marked graphic granite. A large 

 (luartz-reef is exposed in the bed of a creek about a quarter of a mile 

 from the banks of the river at Kalacoon. The quartz is auriferous, 

 assays showing it to contain about thirty-six grains of gold to the ton 

 of the rock. Near the north end of Karia Island on the right bank 

 of the river are situated the abandoned shafts of the D'Urban Mine. 

 These shafts were sunk through a red clay, proljably the decom- 

 position-product of either diabase or of hornblende-schist, to a rather 

 fine-grained granite similar in composition to the rock at the Penal 

 Settlement and at Ansdell's Quarry. In the bed of a creek near the 

 shafts veins and masses of white, glassy, barren (juartz are seen. 



The rapids at Tutruba are small ones, over very fine-grained grey 

 granitite-gneiss. Gneiss is very well seen at Brickbroke Rapids, 

 Marshall Rapids, Kesterbrake Rapids, Warimanibo Cataracts, Ishpot 

 Rapids, Ma|.ishako Rapids, near Tkurishi Creek, Kasira River, and at 

 Kwapanna Rapids, Mapituii Rapids, Espafiol Cataracts, Tarpe Rapids, 

 Crab Rapids, and at Yapemu Rapids in the left channel. The general 



