160 Tlie Geoloipj of lUc G.(>ld FicUh of Jirifi^h Guiana. 



mud or a feldspathic tuff. One mile south-west of the Kuribrong, near the 

 site of the abandoned mission at Ichaura, are the Ichaura or Mission 

 Rapids. These rapids are over compact quartz-porphyry, which is suc- 

 ceeded by feldspar-porphyrite about a quarter of a mile south of the 

 main rapid ; the latter rock is traversed by a broad reef of quartz 

 running east and west ; parts of this quartz-reef, which is slightly 

 auriferous, have been worked for gold at a small stream known as 

 Anderson's Creek, but without much success. 



One mile south of the Ichaura llapids the series of rapids and small 

 cataracts known as the Cobanatuk Cataracts commences. Near the 

 foot of Auritout Rapid, the lowest of the series, large quantities of 

 concretionary ironstone coat the surfaces of quartz-poz'phyry rocks. 

 Masses of quartz occur in the quartz-porphyry near this place. The 

 Col)anatuk Cataracts extending from Auritout to Maurasema, the 

 highest, are over compact quartz-porphyry traversed here and there by 

 thin veins of quartz, and in j^laces containing a little pyrites. Both 

 at the Cobanatuk Cataracts and at Ichaura Rapids the sands lying 

 below them on the sides of the river contain large (juantities of 

 titaniferous iron-ore, and yield an occasional colour of gold. 



From Maurasema to near Pakatuk Cataracts, a distance of about 

 one and a quarter miles by river, or about half a mile as the crow Hies, 

 the rocks are fine-grained, compact quartz-porphyry, this is traversed 

 a little below the lowest Pakatuk Cataract by a dyke of epidiorite 

 trending south-east and north-west, while a little west of this dyke a 

 narrow one of similar rock trends east and west. Below the cataracts 

 a fine-grained diabase occurs, forming some rocks in the river. Near the 

 diabase-rocks the quartz-poi'phyry is of a schistose character, whilst 

 the foot of the lowest of the four Pakatuk Cataracts on both sides of 

 the river consists of compact, fine-grained quartz-porphyry. The 

 Pakatuk Cataracts are over coarse granitite, a broad belt of which 

 crosses the river for a distance of about two and a half miles. The 

 gi'anitite is a handsome grey, somewhat gnei«sose, variety containing pink 

 porphyritic crystals of orthoclase and microcline, and with veins and 

 patches of greenish epidote. In places the granitite contains small 

 crystals of iron and copper pyrites. Near the second cataract from 

 the foot, a narrow dyke of a porphyrite runs through the granitite, 

 while a bx'oad el van of quartz-porphyry traverses the granitite, which 

 is here very porphyritic, at the third cataract. Al)ove the cataracts 

 is a series of small rapids, where in places the quartz-porphyry 

 is traversed by veins of granite. 



A little more than two miles from the top of the cataracts the 

 river crosses a narrow d3^ke of epidiorite, trending from north- 

 east to south-west ; and in the neighlwurhood of Ekureparu Creek, 

 about four miles south-west from the head of Pakatuk, the many 

 rocks which are exposed on the banks and in the river consist of 

 epidiorite. Near the mouth of the Ekureparu Creek the river flows 

 for about three miles from the north-west, and about two hundred 

 yards north of the mouth of the creek a dyke of dial)ase trends north 

 east and south-west, while about one hundred yards further another 



