162 Thd Geology of the Gold Fields of British Guiana. 



From Waracabra to near Waratuk Rapids the only rocks seen are 

 sandstone ; below Waratuk Ra^^ids the river traverses for some distance 

 quartz-porpliyry, and the lower parts of the rapids are over this rock. 

 The main rapids are over coarse diabase, which, in places, has an almost 

 granitic structure. The variations in its structure are well seen on the 

 portage-path round the rapids and at the upper landing. Two hundred 

 yards above the rapids the river passes through quartz-porphyry. 



About six hundred yards west of Waratuk coarse diabase is again 

 seen, and about half a mile from the rapids a dyke of fine-grained diabase 

 crosses the river from north-east to south-west. Half a mile south-west 

 of this dyke the river is crossed by diabase of fine texture trending north- 

 east and south-west. About a quarter of a mile further west diabase 

 rocks of medium texture are exposed on the north-west bank of the river, 

 near the moutii of a small creek ; while two hundred yards further 

 a belt of coarse-grained diabase trending- somewhat west of north occurs. 

 The hills from near Waratuk to near this place iti many instances resemble 

 more r iabase hills than sandstone ones. A little distance beyond 

 the diabase rounded masses of porpliyrite occur in the bed of the river 

 and on its south-east bank. Diabase is also seen beyond these exposures 

 on the northern bank of the river. Three-quarters of a mile from here 

 a broad dyke, apparently about eighty yards across, of very coarse- 

 textured diabase strikes north-east and south-west across the river ; and 

 two hundred yards beyond it a belt of light-red indurated sandstone, 

 altered to the hardness of quartzite, crosses the river, dipping at an angle 

 of about 20" to the south-east, this dij) being probably due to the eleva- 

 tion of the sandstone b}^ the intrusion of diabase which has induraterl 

 and partially bleached it. For the next three-quarters of a mile only 

 sandstone is seen, but at a little more than a quarter of a mile from 

 Tukeit Landing a dyke of very coarse diabase traverses it. All 

 the rocks at Tukeit, and above and below Tukeit Cataracts, are 

 much indurated sandstone. The sandstone not unfrequently shows 

 curre II t-bed ding. 



The gorge of the river from Tukeit to the foot of the Kaieteur is 

 through more or less indurated sandstone and conglomerate. The path 

 from Tukeit Landing to the Kaieteur Plateau crosses the Orimetuk 

 Creek at about a mile and a half from the landing. The creek aff'ords 

 a succession of excellent sections of the sandstone, which is, as a rule, 

 red in colour and not much indurated. In the course of the creek, up 

 its gorge at a level of about six hundred feet above the river, there is an 

 interesting section clearly showing the relationship of the sandstone and 

 diabase. Here a sill of coarse diabase, about eighty feet in thickness, 

 cuts through the sandstone. Below the sill the sandstone has lost its red 

 colour and is bleached ; in places it has been contorted by the intrusive 

 rock, and for a depth of two or three feet it has assumed the physical 

 characteristics of quartzite. At the contact the diabase of the sill is very 

 compact and fine-grained, but this chilled edge is thin, and soon passes 

 into the coarse-textured rock of which the mass of the diabase is composed. 

 The upper part of the sill shows another chilled edge, and the sandstone 

 above it is for some distance bleached and altered to a very hard 



