336 On the Chemical Geology of the Gold-fields of California. 



lost in the water-bath 059 per cent, of moisture ; and by subse- 

 quent ignition the further loss amounted to 8*46 per cent., thus 

 making the total loss 9*05 per cent. Another piece of wood 

 from the same locality lost 0*56 per cent, at 212°, and 8'43 per 

 cent, by subsequent ignition ; in this case, therefore, the total 

 amount of water contained was 8*99 per cent. 



The assay of several specimens of the cementing pyrites showed 

 that it invariably contained a small but very variable amount of 

 gold. In order to ascertain whether this exists in the form of 

 water-worn grains mechanically enclosed within the sulphides, or 

 in the form of spongy and filamentary particles similar to those 

 met with in the pyrites of auriferous veins, I dissolved various 

 samples in nitric acid, and afterwards subjected the residues to 

 microscopical examination. In this way I detected granules of 

 the precious metal which had evidently been worn by the action 

 of water, whilst others appeared not to have been subjected to 

 such attrition. However, on examining pyrites forming the 

 substance of various fossilized trees, I was unable, when the 

 samples were taken from the inside of the trunks in order to 

 avoid the possibility of accidentally attached particles, to detect 

 an appreciable amount of gold, even when the assays were made 

 on several hundred grains of the material ; but my experi- 

 ments were conducted on specimens from one locality only 

 (French Corral), and in Australia very different results appear to 

 have been obtained. Mr. Ulrich states that l< in the gold-drifts 

 pyrites is often found incrusting or entirely replacing roots and 

 driftwood; such specimens very quickly decompose on exposure 

 to the atmosphere, and samples have, on assay by Messrs. Dain- 

 tree, Latta, and Newberry, yielded from a few pennyweights to 

 several ounces of gold per ton." According to Mr. H. A. 

 Thompson, "a beautiful specimen of crystallized iron pyrites, 

 deposited on a piece of wood taken from the drift immediately 

 below the basalt at Ballarat, gave, by assay, 40 oz. of gold per 

 ton ; and in another case, where only the pyrites from the centre 

 of an old tree-trunk was examined, the yield was over 30 dwt. 

 of gold per ton. Some of the fine dust obtained in washing out 

 the gold at the Royal Saxon claim, Ballarat, yielded, by assay, over 

 15 oz. of gold per ton. When placed under the microscope, this 

 dust was seen to be composed of minute crystals of pyrites ag- 

 gregated into round pellets from g^ to T J- ff of an inch in dia- 

 meter, the surfaces being roughened by the projecting angles of 

 the crystals, and unwater-worn"*. 



[To be continued.] 



* Notes on the Physical Geography, Geology, and Mineralogy of Vic- 

 toria. By Alfred R. C. Selwyn and George H. F. Ulrich. Pp. 36. (Mel- 

 bourne, 1866.) 



