3*2 On the Rocks that afford Gold Dust 



Mr Rengger some time ago gave an account of the auriferous 

 sand of the Aar, the Emme, and the Ilsis, in Switzerland, which 

 he had an opportunity of observing himself. It occurs diffused in 

 the sand and gravel of the bottom of the valleys watered by these 

 rivers. When the height of the water occasions the river to 

 cany off part of its banks, the auriferous sand is deposited at 

 the first place where the rapidity of the current finds an ob- 

 stacle. The sand, after it has been deprived of the lighter 

 parts, such as clay, calcareous earth, &c. consists of small grains 

 or plates of gold, magnetic iron, zircon, garnet, spinelle, &c. 

 The Aar, from its exit from the Lake of Thun to its arrival 

 at Jura, flows only through sandstone mountains, as is also the 

 case with the streams which it receives in its course. The 

 Reuss and the Limmat have deposited the debris of the Alps 

 in the bottom of a lake. The only exceptions are the Saune, 

 the two Emmes, and the Sihl, which rise in the alpine limestone. 

 The sandstone and coal deposits appear, therefore, to be the beds 

 from whence the different parts of the auriferous sand have been 

 carried into the basin of the Aar. 



The author has analyzed varieties of sandstone from different 

 countries, as from Staeffelbach, Maegenwyl, and Bollingen, and 

 found magnetic iron in them. He presented to the meeting 

 of Naturalists in Zuiich grains of iron taken from pulverized 

 sandstone from the latter place. If the proportion of the gold 

 to the iron be taken as a scale, the former must occur in this 

 standstone in so small quantity, that a trial made on the large 

 scale alone could succeed in extracting it. 



M. Roulein, however, some years ago, found gold in the 

 sandy marl which belongs to this formation ; and small scales 

 of gold have been observed in the pebbles of nagelfluh quartz 

 of the same formation. The constituent parts of the auri- 

 ferous sand seem to have been brought together from sand- 

 stone mountains, and deposited by natural washing. This 

 washing had undoubtedly commenced during the excavation of 

 the valleys. The heavy parts of the broken-down matrix re- 

 mained, the light parts were carried farther, and the parts of 

 the auriferous sand, after traversing large tracks of ground, 

 and after a long series of ages, were gradually compacted, until 

 at last they appeared under the form of mud. The opinion 



