Proceedi^'Gs of tee Polytechnic Association. 899 



running parallel with the drills are nnitbrmly more productive than 

 others ; and it not nnfrequently happens that a portion of the rock, 

 sufficiently rich to be worked with advantage, is separated from another 

 comparatively poor, bound by a distinct heading on false wall; that, 

 as a general rule, the most productive veins contains a good deal of 

 sulphide disjerminated. In 1862 the wn-iter could have purchased 

 1,000 tons in Grass Valley di tlie sulphide tailings from one mill for 

 twenty dollars per ton, which at present could not be had for $100 per 

 ton ; tliat, ais a gpneral rule, those veins which contains tlie sulphides 

 in abundance, and prove so rich in gold, are situated nearer the siir- 

 fkce, and having, after thousands of years, become decomposed, the 

 inclosed gold has been liberated, and the quartz is found to be 

 stained ; but when gold occurs in a hard white quartz, free of sul- 

 phides, it is mostly in visible flakes and granules, liot rich in veins ; 

 and though they afforded fine specimens in the early days of the gold 

 producing, such veins are not often regularly and remuneratively 

 productive. By taking the vein stone from a gold bearing rock, and 

 examining the wall rock carefully, we will find that the latter has 

 little furrows, as though the lode had been pushed upward, which 

 indicate the direction the dip of the rich streaks. Sometimes gold 

 occurs in nests and pockets apparently distributed without rule; at other 

 times it is more uniformly disseminated by cross sections of veins ; 

 there is also great density ; in one lode the metal is nearly all on one 

 side of the vein, in another lode, similarly situated, it is chiefly on 

 the other side, while in a third, but rarer case, it forms a plane or 

 leaf in the middle of the lode. 



Adjourned. 



December 16, 1869. 



Professor S. D. Tillman in the chair ; Mr. C. E. Emery, Secretary. 

 The chairman presented the following notes on scientific progress : 



New Crystallized Silver Amalgam. 

 From the Paris Comptes Eendus, we learn that at the government 

 mint, in Bordeaux (France having two other mints, one at Paris and 

 another at Strasbourg), there was left standing in an ii*on bottle ^ 

 quantity of about ten kilos of that metal, which had been used to 

 extract silver out of some refuse residues. On filtering chamois 

 leather, there remained upon the filter a certain number of well- 



