104 Tlte Geoloiji) of the Gold Fields of British Guiana. 



from these effects, the movements can be regarded as " pseudo-olacial." 

 He stated that the downward movements of the deposits on hill-sides 

 resuhed in l)reaking up the quartz-reefs, whether original fissure-reefs 

 t)r veins of secondary quartz which occurred in them. And he described 

 the formation of the coarse angular quartz-gravel so characteristic of 

 many of the jjlacer-woi kings as follows : — 



" That we must discard the mechanical force of running water if we 

 wish to explain the origin of the Guiana placers may be inferred from 

 the fact that in many of the placers the gold-bearing gravel consists 

 entirely of sharp-edged quartz pieces, extends evenly from hillside to 

 hillside, clear across the valley, and is usually for the total distance 

 evenly productive. This angular quartz has not been carried from the 

 hillside to the valley by any running water, but, as I shall show, 

 exclusively by the pseudo-glacial movement of the cumulative clays. 

 The topmost layers of these clays is ever kept saturated with water, 

 which, while draining off, lessens the friction l^^ween the molecules of 

 the clay, and in this way becomes responsible for its plasticity. To 

 illustrate and to prove this contention I wish to cite the following 

 observations : — The Omai placers, situated on the left bank of the 

 Essequibo River, have yielded from a territory not exceeding 300 by 

 4,000 feet 65,000 ounces of gold. The gravel of this placer 

 consists of ironstone and quartz pebbles, with a liberal amount of 

 angular quartz, which occasionally exhibits large amounts of free gold. 

 The first owner of this placer spent some money to find the reefs to 

 which he attributed the placer gold. An Australian miner, whom he 

 employed, was lucky enough to strike a reef two feet thick, and of 

 wonderful richness. This vein dipped about 12° towards North-west. 

 Where it entered the clay it was split, but the main point of my 

 observation is that its outcrops, greatly broken up, were deflected in 

 the direction the clays were moving. Two i>ther reefs above this one, 

 but approximately parallel with it, outcropped on the west side of the 

 same hill, the slope of which was slightly steeper than the pitch of 

 the vein. Both reefs were broken up into pieces of different size near 

 the surface. Drifting upon them revealed the fact that the upper vein 

 was crushed for a greater distance than the lower one, but just this 

 part showed unmistakable evidence that the clays had been sliding 

 upon its surface, while the upper one was crushed to pieces, often 

 lying inches apart. 



" This jiseudo-glacial movement may even produce an inversion of 

 reefs. At Anderson Creek, a tributary of the Potaro River, I was 

 charged to examine a reef, whose outcrop could plainl}^ l)e followed for 

 some hundred feet. The outcrop appeared upon the left bank of the 

 creek, in the bed of which angular quartz pieces predominated. The 

 slope of the hill was slight. Throwing out ditches revealed the 

 presence of a layer consisting entirely of angular quartz pieces, which, 

 the nearer we approached the hilltop, were buried deeper and deeper 

 in the clay. This layer, however, came to a sudden stop, and then we 

 just as suddenly struck the reef about six feet below the surface. 

 Ditching higher up the hill failed to reveal a single piece of ([uartz. 



