General Geology. '23 



country are covered up with strata of laterite, frecjuently over one 

 hundred feet in depth, and in places interspersed with nests of secondaiy 

 quartz, or traversed by veins and sti-ingers of quartz, or, less often, Vjy 

 lenticular layers of secondary quartz, closely resembling, when cut 

 through by mining, shafts, tunnels and trenches, true quartz-reefs. 

 The (juartz rock in all these forms is not unfrequently auriferous, the 

 metal being dispersed through it in a very irregular manner, especially 

 in the larger lenticular laj^ers, which in many parts are nearly, or even 

 entirely, barren of gold, and in others are " bonanzas " carrying at rates 

 from twenty to, in places, several hundreds of ounces of the precious 

 metal to the ton of the rock. Unfortunately hitherto these bonanzas 

 have proved few and far between ; but there is no reason for assuming 

 that they will not be found in many places in the enormous area of the 

 laterite deposits which up to the present has not been prospected, as they 

 have been in similar places at intervals in the past. Gold also occurs 

 as paint gold, as gold dust, and as nuggets of very varying sizes in the 

 laterite. 



Of earlier age than the diabase is the sandstone and conglomerate 

 series. It constitutes the greater portion of the Pacaraima mountains, 

 and spreads westwardly into Venezuela. A similar formation occurs 

 in Brazil, and in all probability is part of the same massif as the 

 Guiana one. Wherever it occurs it appears to be unfossiliferous, and 

 hence we have no palfeontological evidence with regard to the 

 geological period at which it was deposited. Two conjectures 

 have been made as to this. C. B. Brown arrived at the conclusion, 

 on what appears to me to be somewhat defective evidence (its, in 

 parts, reddish colour, its unfossiliferous nature, and its being penetrated 

 by masses, dykes and sills of greenstone — diabase — as are sandstones 

 of Triassic age in North America), that it is an equivalent of the 

 New Red sandstone. In Venezuela its relationship to rocks of known 

 age is said to be recognisable, and it is stated to be of Cretaceous 

 age. A like conclusion that the northern parts of the formation are 

 of Cretaceous age has been arrived at in Brazil. If these views are 

 correct, the later outbreaks of diabase, which are, directly or indirectly, 

 the causation of manv of the auriferous deposits of British Guiana, 

 must be either of Cretaceous age, or belong to the Tertiary or to a later 

 period. And as there is a very great resemblance in the magmatic 

 character of the Guianan diabase, and of the lavas of the West Indian 

 province, whose outbreaks are clearly of Tertiary and of present age, 

 the assumption of the relatively recent age of tlie diabase is a plausible 

 one. As will be mentioned in a later chapter, the diabase shows no 

 signs of the effects of the regional metamorphism which has materially 

 affected many of the rocks underlying the sandstone formation. 



The only evidence available in this colony with regard to the 

 sandstone and the geological period of its formation is that wherever its 

 base has been seen it occupies an analogous position to the Torridonian 

 sandstones of the Scottish Highlands, to which the sandstone has a 

 close resemblance in constitution. It lies invariably on the presumably 

 Archean rocks of the colony ; and its constituents, as far as I have been 



