32 On the Geological Distribution of Gold. 



In South America, the fluvial gold (the miners' " oro-cor- 

 rido") in all auriferous localities, presents a characteristic 

 that is not so generally met with in other parts of the "world, 

 hecause the fluvial gold, whether from the North or the South 

 of this continent, is found of a flat, smooth, rather ovoid 

 shape with well-rounded outlines, sometimes bulky and more 

 irregular in form, but generally clean, and never attached to 

 any mineral or metallic compound whatever. There are cer- 

 tain localities where the gold-particles assume such an equality 

 in their exterior, that they may be compared to some of our 

 well-known cereal productions. This fact is so generally 

 known and attended to, that on viewing " the grain" of the 

 gold, the locality is recognized as well as the commercial 

 value. 



The Spanish Government obtained a considerable income 

 by the so-called " quinto-del oro," or the tax paid on gold- 

 dust, and it may be worthy of notice that during nearly 

 three centuries, while the fluvial mines produced great quanti- 

 ties of gold, there were not worked in the whole extent of 

 South America hah 1 - a- dozen auriferous veins, and these with 

 a very scanty produce. Even in later years, when more at- 

 tention has been given to the gold producing rocks, only a 

 limited number of the same have proved commercially pro- 

 ductive, and the greater number of such veins produce their 

 gold of a lower quality, containing, as it does, a greater alloy 

 of silver than the fluvial gold. 



One among several fluvial auriferous deposits of South 

 America, remarkable for their geological position, will here 

 be briefly noticed, as existing on the undulating table-land of 

 El Valle de Osos of Antioquia. This plain, at an elevation 

 of 9150 feet above the sea, constitutes one of the most 

 elevated, isolated flat localities of the district, presenting 

 no mountain ridges, or, as they have been called, 

 " backbones," diversified only by a single perpendicular hill, 

 bordering on the northern part of the plain — which is sur- 

 rounded with the valleys of Medellin and Cauca, over which 

 it is elevated from 4000 to 7000 feet. The fluvial detritus, 

 occupies somewhat more than 150 feet in thickness, and is 

 spread over an area of 100 square miles, resting on granite, 

 more or less decomposed. Here the observer certainly finds 

 no mountains where the auriferous rock might have contri- 

 buted to provide for the auriferous gravelly sands resting 

 on the granite bed. This deposit has been worked for about 

 1 50 years, though only in the rainy periods of the year, and is 



