PECULIAR ACCRETIONS. 729 



sulphate of lead. Whatever their origin, they are formed of galena. The sample 

 assayed was prepared from five specimens from the following smelters: 



dimming & Finn 2 



Grant 2 



Raymond, Sherman & McKay 1 



Total 5 



The whole accretion assayed 45 ounces of silver to the ton. It was separated by 

 the sieve into 



Powder 91.25 



Metallic lead grains 8. 75 



Total ; 100.00 



The powder assayed 35 ounces and the grains 148.5 ounces to the ton. 



When mattes and accretions are not thrown away pell-mell with the slags, they 

 are always roasted in heaps in Leadville. A mixture of such roasted mattes and 

 accretions from Billing & Eilers's smelter was assayed ; it consisted of two fine speci- 

 mens, yellowish white and reddish on the surface, full of large cavities, and having a. 

 blackish fracture ; free sulphur was visible throughout the mass. It was separated by 

 the sieve into 



Powder 97.96 



Grains . . 2. 04 



Total .' 100.00 



The powder assayed 8.25 ounces of silver to the ton. 1 



If we consider that the products roasted assayed 22.45 ounces (accretions), 102, 

 71.5, 99, and 66 ounces (mattes), respectively, we may well ask, what becomes of the sil- 

 ver in this ruinous operation of roasting in heaps performed at several smelters? A 

 definite answer is difficult, since if silver is volatilized it is not known in what form ; 

 but it seems probable that, since the roasting takes place in the open on the slag- 

 heap and the roasting heap is periodically leached by rain, silver may be carried away 

 in the state of sulphate. 



Peculiar accretions The following analysis has been made of a very peculiar 

 accretion found at Messrs. Gumming & Finn's smelter. This accretion is half black 

 and half yellow and looks like a mixture of galena and orpiment. It was separated by 

 the sieve into 



Powder 75. f>4 



Lead grains 24. 40 



Total 100.00 



The whole accretion, powder and grain, was analyzed (see Analysis XLIII), and 

 more interesting results than those obtained could scarcely have been anticipated. 

 The bright-yellow portion proved to be a peculiar Naples yellow formed of arsenio- 

 aatimonio-stannate of lead; and the whole of the constituents of that portion were in 

 the state of oxides. Here we find a most remarkable instance of concentration, that 

 of tin, which apparently exists ouly in traces throughout the camp, and that of anti- 



1 All the assays of accretions were made in the laboratory of the Survey. 



