The Lower Essequiho River and Cuyuni River District. 125 



It is intersected by a vein of a greenish-grey massive granitoid al rock 

 of medium texture, consisting of white zoisite with an abundance of a 

 very light brownish-green hornblende, and having a specific gravity of 

 2*97. This rock closely resembles that of the dyke of zoisite-amphi- 

 bolite which traverses the gneiss near Takkarri Rapids below the belt 

 of amphibolite. 



In the eastern channel, in a position corresponding to that where the 

 belt of amphibolite occurs in the main course of the river, there is a 

 small rapid, succeeded in the course of a mile or so by a long series of 

 rapids and low cataracts known as the Upper Mariwa Falls and as the 

 Akariwa Cataracts. Below the small rapid is a purplish-tinged mica- 

 gabbro or gabbro, in which the masses of augite have been changed 

 in places to chlorite and serpentine, and in parts to abundant plates of 

 brown biotite by metamorphic action. 



Below the foot of the long series of rapids is a dark-grey gneissose 

 rock of specific gravity 3-08. This is related to the one just described, 

 and consists in part of a fine-grained gabbro, and in part of a gabbro 

 with the augite more or less completely replaced by green hornblende. 



The foot of the rapids is over a fine-textured darker-coloured rock 

 of specific gravity 2-97. In this the progress of metamorphism has 

 extended farther than in the one last described, by far the larger ^jortion 

 of the augite being replaced by green hornblende, some large masses of 

 the latter, however, have scattered thi'ough them numerous small 

 kernels of unaltered augite. The rock shows clearly the commencement 

 of schistosity. The middle and upper parts of the rapids Jire over a 

 gneissose or schistose rock varying a good deal in texture, the finer- 

 textured varieties having a specific gravity of 2"81, the coarser kinds one 

 of 2*93. These vary mainly in their relative contents of labradorite, of 

 epidote, and of hornblende, and represent the completely metamorphosed 

 stage of the gabbro, being in places typical epidote-hornblende-schist.s. 



The Akariwa Cataracts are caused by one of the spurs of the Blue 

 Mountain Hills, as the Mariwa and Arawak Matope Cataracts are by 

 other spurs. 



In the western channel the zoisite-amphibolite band at Wariri, at 

 about 200 yards above the mine landing, is succeeded by granitite- 

 gneiss and hornblende-granitite-gneiss. A large I'eef of glassy-white 

 quartz traverses the gneiss about half a mile above the landing, the 

 quartz yielding to assay about twelve grains of gold per ton of the rock. 

 The Arimu Creek falls into the Cuyuni on its right bank about a 

 mile west of Wariri. 



About a quarter of a mile above the mouth of the Arimu are the 

 Maritout Rapids. The lowest rock seen in these is a white mass of 

 friable muscovite-grauite. The rapids are caused by a belt of epidiorite 

 passing to a hornblende-schist, probably an off-set from the broad belt of 

 amphibolite, epidiorite, and hornblende-schists described as occurring 

 near Wariri, and at the Akariwa Cataracts, and as giving rise to the 

 Blue Mountains. At the head of the rapids the rock exposed is an 

 epidote-hornblende-schist. Above Maritout a feldspathic gneiss occurs 

 made up of pink and greenish-grey layers of feldspar and fine-grained 



