Descriplive Geolixjij. Ill 



From about half a mile above Mazawini Landing the river flows 

 through a district of gneissose granitite and gneiss. The rocks for about 

 fdur to live miles are mainly grey gneissose granitite. Above this the 

 country consists of a fine-grained grey epidote-granitite-gneiss, which is 

 traversed at the Towakaima and at the Mazawini Cataracts by veins and 

 narrow belts of grey and pink granitite and of diorite. In places 

 in this part of the district masses of amphibijlite occur in the gneissose 

 complex, and these may have given rise to the hills of red laterite which 

 are not unfrequent. 



The reaches of the Barama River above Towakaima Cataracts, as far 

 as they have been examined geologically, traverse a country of more or 

 less schistose porphyrite intersected by belts of hornblende-schist. 



The Waini River. — There are some rocks and a small island, known 

 as Granite Island, in the Waini River about a mile below the mouth of 

 the Baramanni Creek. These are formed by a mass of grey granite, 

 varying in texture from fine-grained to moderately coarse. On the left 

 baixk of the river, between three and four miles above Granite Island, 

 another exposure of the granite occurs, while about seven to eight miles 

 higher up the river, and about three quarters of a mile from its right 

 bank up the Canayaballi Creek, huge masses of a coarser-grained 

 variety of the grey granite are exposed. The low hills to the south and 

 south-west of this appear to be of granitic origin. 



These exposures of granite are of considerable interest, as true 

 granite, consisting of orthoclase with some oligoclase, quartz, biotite and 

 a good deal of muscovite, is of rather rare occurrence in the portions of 

 the colony I have traversed ; the only other localities known to me in 

 which granite is found being near the junction of the Cuyuni and 

 3Iazaruni Rivers, on the upper reaches of the Pomeroon River, and 

 above the lower cataracts of the Kuribrong River. 



I have not visited the Waini River ab(jve its junction with the 

 Barama. The following account of its structure is taken from pages 36 

 and 'il of Brown and Sawkins' geological reports, and, in mv opinion — 

 having examined their specimens from the Waini River petro- 

 graphically — is j^robably accurate : — 



" On the River Waini, above its junction with the Barama, the left 

 bank, close to the river's edge, attains an elevation of 1 5 feet above the 

 highest tide, and extends eastwardly and southwardly as a level table- 

 land. The soil is loose and sandy, and the few small rocks upon it are 

 granitic. All the right bank is low and swampy, and composed of 

 alluvium. Just before reaching Anapiri both banks become slightly 

 elevated, a foot or two above the river. This place is the head of the 

 tide, and no rocks whatever are to be seen on the river up to this poiiit. 

 They first appear a short distance above this, and continue to be seen 

 to and beyond the Waini Falls, and are chietlj^ gneiss or granite. Mica 

 schist and a grey granite also occurs in few spots, but chiefly at the 

 falls. Few true quartz veins are to be seen, but veins of a coar.se- 

 grained crystalline granite, having very much the appearance of quartz, 

 are of frequent occurrence. In these the quartz is semi-transparent and in 



