20 Geology of the Gold Fields of British Guiana. 



argillaceous soils, and in others give rise to long narrow ridges somewhat 

 raised above the general level of the land which they traverse. Their 

 mode of occurrence indicates that they are purely local modifica- 

 tions of the alluvial deposits, — sands sejjarated from the mass of the 

 marine silt l)y the action of local currents and of the waves, — and thus 

 tlie sand-beds form more or less lenticular beds occupying, as a rule, 

 no great area. They are, in my opinion, very distinct from the beds 

 of sand which characterise various 2:)hases in areas where the land 

 is either rising or falling to any extent in the vicinity of a shallow 

 sea. 



The general evidence indicates that Bi'itish Guiana occupies one 

 of the most stable areas of the earth's surface, — one which has been \ ery 

 slowly rising through long ages, — this slow movement having given rise 

 to the low rapids which usually mark the termination of the tide-way in 

 the rivers, and possibly which has so altered the contour of parts of the 

 continent on which the colony is situated as to change the main lines 

 of drainage, and thus to make the rivers relatively small streams 

 traversing the deeper parts of the courses and valleys ex'oded by their 

 predecessors in earlier periods. During a stage in this slow upheaval 

 the low hills already mentioned as occurring in a few places in the 

 alluvial const-land were in turn rocks and small islands in the shallow- 

 ing sea which then surrounded them, as now they are surrounded by 

 an apparently unbounded expanse of forest or of marsh. 



A remarkable feature in parts of the alluvial coast-land is the 

 occurrence of extensive beds of a kind or peat. This is locally known 

 as " pegass," and consists of the more or less altered remains of ferns, 

 mosses and sedges, and of other marsh-loving plants. It resembles in 

 its general characters the upper layers of vegetable matter which are 

 found in peat-bogs in temperate climates. As far as my observations 

 go it is never as compact as in true peat. This is pro))al)ly due to the 

 deposits of it being seldom more than from two to four feet in thickness. 



As pointed out by Sir Charles Lyell in his " Principles of Geology," 

 a large portion of the sand and clays of the alluvial deposits has been 

 brought by the currents from the mouth of the Amazon River ; the 

 burden brought by the present rivers of the colony from the higher 

 districts through which they How having been, during recent periods, 

 a very subordinate factor in the accumulation of this widespread 

 formation ; although perhaps in earlier times, before the land had risen 

 to its present level, the river-borne silt may have contributed a larger 

 quota to the mass. 



The Foreat Lands and Residuary Deposits. — The alluvial strata 

 extend to depths varying from five to, in places, as much as thirty-five 

 miles from the coast-line, and rest upon beds described by C. B. 

 Brown as " sand and clay deposits." This widespread formation may 

 be seen for many miles along the courses of certain of the rivers, as, for 

 instance, the Barima and the Barama in the North-Western district, the 

 Essequibo and the Detnerara Rivers. I have included in the alluvial 

 deposits the portion of Brown's sand and clay deposits which appears to 



