112 TJie (Geology of the Gold Fields of British Guiana. 



crystals of over an inch in length ; the feldspar is milk-white and of the 

 same dimensions, while the mica is in crystals of one and a half inches 

 in diameter and half an inch thick, of a dark colour. On sjDlitting the 

 mica into thin plates it is of a fine silver-white colour. On all the sand- 

 banks at the bends of the river the plates of silver- white mica are to seen. 

 " A huge dyke of fine-gniined grey granite, running across the river 

 nearly east and west, and of about 200 yards in width, forms the falls, 

 which are about 20 feet in height. The rocks on this river vary in a 

 marked degree from those of the Barama, and on the whole are more 

 gneissic. Hills approach the river in many places, and around the 

 falls are about 120 feet above its level." 



The Fomeroon River. — At Santa Rosa in the Moruca River, at 

 Cabacaburi and at Macaseema in the Pomeroon River, there are low 

 hills of laterite, over parts of the surface of which concretionary 

 ironstone and blocks of quartz occur. These hills show evidence 

 that the laterite has been derived from a foliated rock, in my opinion, 

 probably an epidiorite or a hornblende - schist. Examinations of 

 specimens collected in the higher reaches of the Pomeroon River by 

 Mr. H. Rolleston in 1898, and by Mr. E. Beckett in 1906, showed 

 that it traverses a gneissose country, which is intersected by rolls of 

 a grey, somewhat gneissose granite. The Aranamai Creek, a branch 

 of the Upper Pomeroon River, traverses a country of somewhat 

 complex structure. Near Souarindu on this creek a micro-granite 

 traverses the gneiss, and a silicified tuff — resembling the altered 

 volcanic tuffs found on the Berbice River, and on the Potaro River, 

 above the mouth of the Kuribrong River — occurs. At and near 

 a place called Boatbuilder there are exposures of a fine-grained 

 quartzite, of quartz-porphyry, of feldspar-porphyry, and of a somewhat 

 fine-grained mica-gabbro, closely resembling the rock of the hill at the 

 Barnard Placers on the Isenaro Creek of the Upper Mazaruni River. 

 Near and at the Hiari Rapids on the upper part of this creek, 

 exposures occur of an epidiorite, which in places is much chloritised, 

 and the country consists, in part at least, of a mica-gal)bro very similar 

 to one which is found in the upper reaches of the Mazaruni River. 

 The country is traversed by dykes of diabase. One of these at the 

 Hiari Rapids consists of coarse-textured olivine-diabase, a variety of 

 rock of relatively rare occurrence in British Guiana. 



This country has not been prospected by gold-seekers to any 

 extent, although its geological structure closely resembles that of the 

 diamantiferous and auriferous areas traversed by the Mazaruni River 

 below the Peimah Cataracts. 



The Goldfields of the North-West District. — The principal gold 

 bearing area of the North- Western district is that near Warimba, 

 Arakaka and Manikuru, which extends from the northern bank of the 

 Barima River in a north-easterly direction, along the Kaituma Path 

 towards the Kaituma River, and from the opposite bank in a south- 

 westerly direction to some miles south of Hyma to the Barama River, 



