152 The (reolcxiy of tho. Gold Fields of British Gnlan-i. 



Horublende-granitite-gneiss is very frequently exposed in great 

 rounded masses for a distance of more than three miles from Moco-Moco 

 to Yukurisi Island, and about a mile south of Moco-Moco Creek is 

 traversed by a dyke of diabase striking north-east and south-west. About 

 half a mile south of Yukurisi Island a belt of coarse hornblende-granitite 

 commences, and extends to near the south end of Dehalibanna Island. 

 The granite is seen weathered into sub-angular blocks on the east of the 

 river near Arai-apira Point, and on the mainland, at the point, it contains 

 porphyritic crystals of feldspar, frequently from one and a half to two 

 inches in length. It also contains some caught-up pieces of hornV)lende- 

 gneiss. To the south of Ararapira Point a dyke of diabase, about twenty 

 feet wide, strikes through the granite east-south-east across the river, 

 giving rise to the Ararapira Rapids. The junction of the diabase and 

 granite is well seen. A hundred yards south two narrower dykes occur 

 running parallel to the Ararapira Dyke. About a quarter of a mile 

 north of Dehalibanna Island, granitite-gneiss occurs, and forms the 

 prevalent rock for fifteen miles until approaching the Omai Mountains. 

 At the south end of Dehalibanna Island a dyke, about fifty feet w'ide, 

 of a porphyritic epidiorite, with crystals of labradorite up to two inches 

 in length, strikes south-east and north-west through a sandbank. 



At the north of Arasaru Point masses of gneiss are exposed in the 

 river, giving rise to small rapids. Near Arasaru Creek the gneiss is 

 traversed by an elvan of aplite. At Arasaru southern point three dykes 

 of diabase occur, two narrow ones to the north of the j^oint, each about 

 eight or ten feet across, sending thin tongues into the gneiss, and one 

 to the south of the point, ai^proximately parallel to the others, which 

 curves in its trend across the river from north-north-east to south-west. 

 The latter varies in width from forty to sixty feet, and is capped, in 

 places, with concretionary ironstone. About one hundred yards from 

 the south-west end of the dyke a vein of non-auriferous quartz, about 

 five feet wide, runs through the gneiss in a north-easterly direction. 

 Aljout half a mile south of this dyke, at the southern end of Kwapana 

 Island, a diabase dyke passes through the island in a north-easterly 

 direction. It is visible again a little further south in the river, near 

 the west bank, trending to the south-south-west. In this dj^ke, which 

 is exposed for about a mile, the two directions of the main joints are 

 respectively parallel and at right angles to its trend. Half a mile 

 south of the south-west exposure of this the river is crossed from 

 north-east to south-west by a diabase dyke about twenty feet in width, 

 while between t,wo and three hundred yards south of the latter another 

 trends north-north-east and south-south-west. 



At Akenna North Point a broad expanse of gneiss is exposed on the 

 east bank of the river, with many narrow dykes and veins of diabase 

 traversing it in a north-easterly direction ; and a little south of the 

 Point the gneiss is crossed by two parallel dykes of dial)ase, one of 

 which is fifteen, the other eight feet in width, which trend from east to 

 west. A third dyke crosses the river in a north-easterly direction, 

 somewhat further south, and in part consists of a greenish -coloured 

 porphyritic epidiorite or proterobase. At about a quarter of a mile 

 below this a dyke of diabase crosses the river, trending north-east 

 and south-west. 



