Proceedings of the Polytechnic Association. 703 



in auriferous wealth. He was one of the first geologists to draw a 

 line between early and late rocks in geological history bearing gold. 

 Since then this distinction has been g,bundantly confirmed by Murchi- 

 son, Forbes, and Whitney, and other authorities. He was correct. 

 The Orinoco valley -has never produced gold, either from its rocks or 

 sand*. The Essequibo basin was never visited by Humboldt ; it has 

 never been explored by competent scientists. Much of it is terra 

 incognito to day. Schomberg visited the southeastern portion, but 

 the middle is entirely unknown, and the northwestern Jias been but 

 partially explored. 



In the year 1854, Dr. Lewis Plassard, a French physician, visiting 

 the old miss ion -village of Tubuken, situated on the banks of the Rio 

 Yuruary, went down to this stream for his daily bath, and there and 

 then discovered auriferous quartz among tlie water-worn' rocks of this 

 stream. The Yuruary is the northwest tributary of the Yuruan, 

 which empties into the Essequibo near Georgetown in British Guaiana. 

 Since then, with varying success, this portion of the valley of the 

 Yuruary has been producing gold. The extent, continuity, and rich- 

 ness, and produce of its quartz veins have been well proved, and the 

 fruits thereof have gone to Europe in annually increasing quantities. 



Opposite Tubuken, rising from the south bank of the Yuruary, there 

 stretches oif southwesterly a low. range of mountains for about fifty 

 miles. The width of this range varies from six to fifteen miles. 

 About twelve miles above Tubuken, the Yuruary commences to break 

 through this range of mountains, and by means of this natural excava- 

 tion we. are enabled to learn the mineral constituents of this range of 

 mountains. Expressed comprehensively, they are metamorphic ; in 

 detail, they are honiblendic, talcose, micaceous and brecciated slates. 

 Quartz veins are confined to the talcose and brecciated portions. •The 

 talcose have sufiiered much from decomposition, and appear more as 

 mottled and indurated clays, than as rock. 



The valleys of the Mocupio and the Iguan are the only ones of tliese 

 mountains, save the main valley of the Yuruary, which have been 

 searched for gold. These support, from vein and placer mining, a 

 population of about 2,000 people, living in seven palm-thatched, 

 mud-walled villages, the central one of which is IsTueva Providencia, 

 where is situated the church and oflices of the department, and where 

 resides the curate and prefecto. 



Gold is obtained from its mating in the most rude and'primitive 

 manner, no other machinery is used than the hammer and common 



