Tlie Diammifi/cro/is Arfns. 213 



distaixce of ;il)i)ut five miles from tlie Mazaruiii River, its width being 

 about three miles. The diamaiitiferous beds are gravels situated at a 

 level of about seventy feet aljove the Mazaruni River, and lie on the 

 summits and the sides of low hills and stretches of rolling country. 

 They appear to be in the position of their deposition, and they hive 

 been derived, in part at any rate, from the degradation of the sand- 

 stone and conglomerate formation, outliers of which occur in the 

 neighbourhood. Diamonds are found in the lower layers of these 

 gravels, and also in places in gravels in the valleys which have been 

 eroded through the bedded gravels into the more or less decomposed 

 residua of the granitic and basic rocks which underlie the sandstone 

 and conglomerate formation in this part of the country. The valley 

 gravels are more angular in character than are the bedded ones, much 

 of the quartz they contain having been direct!}^ derived from the 

 decomposed, igneous rocks. 



The characters of the gravel beds on the hills are as folI(jws : The 

 surface layers, as they do in many other parts of the interior of the 

 colony, consist of, in places, almost pure white quartz-sand, and in 

 others of a similar satid more or less stained by the presence of oxide 

 of iron. These surface layers extend to about eighteen inches in depth, 

 and rest upon a varymg depth of a yellowish sandy clay, which contains 

 small angular fragments of quartz, and here and there small patches of 

 sand and gravel cemented by oxide of iron. The sandy clays are of 

 varying depths, from eight to fifteen feet, and h\ their deeper parts 

 graduail}^ become more gravelly : the pebbles also are there more rounded 

 and larger 'u\ size, whilst the pieces of ceuiented material are more 

 abundant. The diamonds are irregularly distributed through this 

 lower deposit, a very few small-sized ones occurring in its upper parts, 

 whilst they are found more abundantly and of larger size as the work- 

 ings gradually pass through the lower parts of the gravelly clays tf) 

 the layers of diamaiitiferous gravel which rest on the bedrock. Mr. 

 Braddon gives two sections of the gravels, in one of which is shown 

 six feet six inches of barren sand and gravel resting on fifteen inches of 

 gravel and grit and four feet of fine sanrl. The latter strata contained 

 a ftw small diamonds. Below them three feet of grey-coloured gravel 

 and sands are shown, which yielded a fair number of diamonds, and 

 rested upon four feet of red-coloured compacted gravel, which contained 

 a relatively large number of the gems. Under the gravels, as bedrock, 

 an absolutely barren kaolin or a red-coloured laterite occurs. The upper 

 layers in these sections undoubtedly owe their grey tinges to the 

 leaching-out of the ferruginous constituents by water charged with 

 organic acids percolating from the humus-bearing topmost stratum. 

 The other section shows a covering of one foot of humus-bearing loam, 

 underlain by three feet of sand and gravel not showing signs of bedding, 

 which rest on a like thickness of grey-coloured bedded sand and 

 gravel. This lies on four feet six inches of red, grey and white grits, 

 sands and gravels, which are underlain l)y one foot of white and 

 red clayey diamantiferous gravel. The gra\"el rests on a bai'ren 

 laterite. 



