On the Geological Distribution of Gold. 29 



quiet process during a great lapse of time. It thus appears 

 beyond any doubt that the pleistocene epoch partook of 

 a preliminary period of inactivity or rest, and that the geo- 

 logical operations Avere carried on in two distinct divisions, 

 which by the existing productions from that time show one 

 partial or peculiar distribution limited to certain localities of 

 our globe, and another more extended or general distribution. 

 The latter is represented by the fluvial detritus, to which 

 has been given the distinctive term of diluvium, and this 

 period and the detritus then distributed shows the earlier 

 of the two fluvial operations carrying gold — the latter of them 

 receiving its distinction by the name of alluvium. 



Diluvial detritus carrying gold and covering the auriferous 

 strata. — The lowest stratum resting on the denuded rock will 

 generally be found auriferous, consisting frequently of sand 

 and pebbles, or sand and gravel, in South America and Cali- 

 fornia, with very rare exceptions, perfectly rounded or 

 waterworn. Boulders and other smaller fragmentary rocks 

 are also found in some localities all more or less waterworn. 

 Clay is not frequently found in admixture with the 

 strata of sand and gravel. Clay, more or less arenaceous, 

 constitutes separate layers, and on the top of these, sands and 

 mud (or finely pulverized mineral compounds) with more or 

 less argillaceous matter, colored by per-oxide of iron, of 

 a variegated hue. Among these superior strata, gold is 

 occasionally found, in the elevated tracts of South America, 

 from about 5,500 feet to 10,500 feet above the sea. Strata 

 of mud, of considerable thickness, occupy the superior 

 portion of the diluvium, being covered with a thin coating of 

 vegetable soil. These depositions consist of most diminutive 

 particles of silica and talc, occasionally mica, being co- 

 loured with per-oxide of iron, light brown and yellow — 

 when in their natural moist state, unctuous ; but when the 

 mass becomes dry, it is nothing but a fine loose powder. No 

 argillaceous matter is found with this, called by the natives 

 "soapy earth," which is well known for its sterility, and 

 where it prevails it seldom covers any productive aurifer- 

 ous detritus. In some localities of South America, a ferro- 

 argillaceous compound with silica, of the colour of rust, 

 several inches thick, appears on the top of the diluvial detritus, 

 covered with a thin coating of vegetable mould. In other 

 localities the very same compound is found at a further depth, 

 covering in the same manner the lower auriferous stratum. 

 This hard compact cement has not proved auriferous. 



