Its The Geohxji/ of the Gold Fields of British Guiana. 



The rocks at these catai'acts are vertically jointed and, on the 

 surface, appear to have a schistose structure. Broken masses of 

 similar rock, with numerous small outlets through which the water 

 falls, form a cataract about half a mile beyond known as Winter's 

 Falls. Some rocks exposed at a small rapid about a mile above 

 Winter's Fall are green- coloured porphyrite, and about two miles 

 Ijeyond a long shallow reach of river, known as Savannah Rapids, is 

 filled with small blocks of similar rock. About half a mile aljove 

 Savannah Rapids a diabase dyke of about one hundred feet wide trends 

 across the river. 



Above this dyke rocks of compact felsite are exposed as far as the 

 long and shallow rapid called "Tramway," where j)orphyrite forms 

 the rocky bed of the river. 



Below Manmakuri Rapid felsite also occurs. 



At Manmakuri Rapid the rock-formation is feldspar-porphyrite, 

 and varieties of this rock are exposed at S Rapids (so called from 

 their shape), Cham])ion Rapid, Guava Rapid, and as far as Haururaru 

 Creek and Landing, a distance of about nine miles along the river. 

 Just above Haururaru there is a small belt of granophyre, succeeded by 

 felsite, which gives rise to a series of rapids known as " Tacuba Falls." 

 The felsite along this series is much jointed at varyii\g angles, and on 

 the surface has a schistose appeai'ance. 



The great mass of rock forming the upper and lower parts of the 

 Christmas Cataracts, which are about one thousand one hundred yarrls 

 in length, is feldspar-porphyrite, vertically jointed in many places, and 

 varying in colour and texture. 



About the middle of these cataracts tlie feldspar porphyrite is 

 traversed by an intrusive dyke of diabase about three hundred feet in 

 width, causing a perpendicular fall of about twelve feet. 



Rocks of feldspar-porphyrite are exposed at intervals in the river 

 from Christmas Cataracts to Bullet Tree Creek. 



A little below Bullet Tree Creek rocks of porphyrite form shallows 

 and islands in the river, while at Brown Ci'eek rocks of feldspar- 

 porphyrite occur. 



