On the Geological Distribution of Gold. 25 



Lower Fluvials. — (Diluvial). 



Plains of Supfa- — about four miles distant from the Marmato 

 veins. The gold is here found in somewhat larger flat grains, 

 thicker, of irregular shape, and rounded outline, even the 

 smallest particle showing a similar form — the larger grains 

 covered with a film of per-oxide of iron, 21. 13-44 carats.* 



Banks of the ancient course of the Cauca River. 



Upper stratum — The gold being lamellar, of irregular shape, 

 rounded outline, and having a smooth, clean surface, some 

 larger particles found with a film of per-oxide of iron — 

 quality, 16. 21-24 carats. 



Lower stratum, being found a few feet below the actual 

 course of this river, resting on a stiff arenaceous clay bed, its 

 gold, existing partly in larger grains, all flat, rather thick, 

 having well-rounded outlines and smooth surfaces, partly 

 with a film of per-oxide of iron, 18. 15-48 carats. 



Gold from the rock, found among the fluvial gold in the 

 Supia plains, distinguished by its fungiform, rough exterior 

 surface and pale yellow colour, some crevices being filled with 

 hydrous oxide of iron — occasionally found, and in very small 

 quantities — quality, 14. 9-12 carats. 



Gold from the rock, found among the fluvial gold of the 

 banks of the ancient course of the Cauca River, in the lower 

 stratum — well distinguished by its rough, irregular, sharp 

 outlines of a fungiform appearance, occasionally found in 

 very small quantities — quality, 15. 3-12 carats; silver being 

 the only alloy with the gold here referred to. 



In comparing the quality of the gold produced from the 

 veins in the porphyry, as already mentioned, where we see 

 that the prevailing quality of the larger quantities of this 

 metal gives, on an average, from 10 to 15 carats, whereas the 

 gold from the higher and lower fluvials of the said neigh- 

 bourhood shows a much higher carat, or ranging from about 

 18 to nearly 22 carats — we certainly have no inducement 

 whatever to presume that the gold among the fluvial depositions 

 has ever occupied the immediate veinstone above. Wherefrom 

 the fluvial gold of a purer nature has originated, as seen in this 

 and many other localities, when duly investigated, is a 

 secondary question ; suffice it, at present, to show, that in a 

 great many districts of the auriferous part of our globe the 

 fluvial gold presents no analogy with that at present existing 

 in the rock. 



* The bright yellow of the film has led to the name of " Oro Colorado" — 

 (red gold. ) 



