STREAM TIN. GOLD IN RIVER SAND. 



297 



of the mines of Derbyshire ; whilst the same mineral rarely assumes 

 that form in the mines of Northumberland and Durham, but is crys- 

 tallized in other forms, which are equally rare in the Derbyshire 

 mines. Fluor spar, and sulphate of barytes, have appropriate forms 

 in different districts, from which any deviations may be considered 

 as varieties. The causes which occasioned this diversity of second- 

 ary forms in minerals, whose constituent parts appear by chemical 

 analysis to be precisely the same are unknown ; nor are we able to 

 explain in what manner the crystals before mentioned have disap- 

 peared ; but these facts prove, that the powers of nature extend be- 

 yond the present limits of science ; and it is more consonant with 

 the true spirit of philosophy, frankly to acknowledge our ignorance, 

 than to form systems from imperfect data, which can serve only to 

 perpetuate error. 



Metallic ores in rounded fragments, and grains of native metals, 

 are frequently found in the sands of rivers ; they have been car- 

 ried there by torrents or inundations ; the rocks in which they 

 were originally formed, having been disintegrated or decomposed. 

 The metals gold, and platina, being indestructible by the action of 

 air, water, or the mineral acids, remain for ages unchanged, in the 

 form of minute grains. The oxide of tin is a very heavy and hard 

 mineral ; and it is owing to its weight and indestructibility, that it is 

 found in the sands of rivers, or on the sea shore, where it sometimes 

 occurs in considerable quantities, and is separated from the sand or 

 alluvial soil by directing streams of water over it : hence such works 

 are in Cornwall called Stream Works. With the pebbles of tin- 

 stone, there are fragments of granite and other rocks, which serve 

 10 indicate from what mountains in the vicinity the stream tin has 

 been washed out. Particles and small pieces of gold are sometimes 

 found with stream tin, in the sands of Cornwall. 



Gold being, as before stated, less subject to chemical change than 

 the other metals, is found in the sands of rivers in various parts oP 

 the world, particularly in Africa and South America. A consider- 

 able part of the gold obtained frorn Africa is procured by washing 

 the sand of rivers ; it is found in small grains called gold dust. It 

 has been remarked, that in certain parts of rivers, the sands were 

 rich in gold, which seemed to be renewed after heavy rains, and yet 

 but litde gold was found in the sands higher up the river. No satis- 

 factory explanation has been offered, respecting the hmitation of the 

 auriferous sands to certain localides. Facts have, recently, been 

 stated to the author, by a gentleman connected with the gold mine 

 companies in North Carolina, which appear to elucidate the period- 

 ical renewal of gold in the African rivers. About the year 1810, 

 gold was found in the beds of several rivers in North Carolina : 

 one mass was obtained weighing 2Slbs. Afterwards grains of gold 

 were discovered in the beds of several of the rivers and brooks both 

 of North and South Carolina, and of Georsjia. For some years 



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