Descriptive Geology. 113 



between the landing at Mazawini and the Takutu Creek. This 

 country consists of many more or less parallel ranges of relatively low 

 hills with narrow intervening valleys, and it is intersected by numerous 

 gullies and ravines. 



The Warimba district is traversed by a range of diabase-hills, the 

 rock of which is intrusive through a country of sericite, chlorite and 

 actinolite schists, probably derived from the metamorphism of porphy- 

 rites and other rocks of intermediate composition. 



The Arakaka and Manikuru districts are of similar geological 

 structure. They consist of low ranges of hills of deep-red laterite, the 

 surfaces of which are in places covered with concretionary ironstone 

 and with quartz-gravel, whilst large blocks of quartz are frequently 

 found on them. The valleys between the ranges generally are eroded 

 into the schistose country, and contain alluvial deposits of very varying 

 thicknesses, consisting of auriferous quartz-gravel intermingled with 

 concretionary ironstone, and with small pieces of more or less decom- 

 posed schistose rocks, which are covered by ochrey-coloured layers of 

 alluvial earths. 



The general trend of the foliation of the schists and of the gneiss 

 in the neighbourhood of the Arakaka district is north-east and 

 south-west. 



The hill ranges follow this general direction, and in many places 

 along them great masses of diabase are exposed. 



The bulk of the massif of the higher parts of the hills appears to 

 have been diabase. But the numerous shafts sunk through the 

 laterite, resulting from the decomposition in situ of the diabase, have 

 frequently passed into dark-red laterite, showing a foliated structure, 

 and in some of them — the Barr- Robertson Mine, the Barima Mine and 

 the Gates Mine — the shafts have passed through more or less decom- 

 posing masses of grey rock showing foliation and which are altering 

 into dark-red laterite. These masses have been found on petrographical 

 examination to consist of an amphibolite or epidiorite, showing more or 

 less clearly a commencing schistose structure, or which are in places — 

 as, for instance, the country rock of the reef at the Barima Mine — well- 

 marked actinolite-schist. 



The laterites are therefore the products of diabase and of amphi- 

 bolite, epidiorite and hornblende-schist. 



In many places the altered rocks and their residuary decomposition- 

 products, so common in this district, are traversed by reefs of auriferous 

 quartz, and the residuary clays not unfrequently contain large 

 quantities of more or less auriferous quartz, either in the form of 

 angular gravelly fragments, or in that of narrow veins and intersecting 

 threads. 



The Five Star and Rocky River Goldfields are situated about 

 thirty miles west of Arakaka, and are in a district of epidiorite 

 and hornblende-schist, the workings being in laterite, and in the 

 alluvial deposits resulting from it. 



The auriferous district, situated mainly to the east of Hyma, and 

 bounded roughly by the Takatu Creek, the Barama River, and the 



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