NOTES ON THE MINERALS FOUND NEAR BRISTOL. 75 



found as a heavy black powder it is known by the name of 

 ^*'Wad." In many rocks of Carboniferous, Devonian, Liassic, 

 Triassic and Oolitic ages, it may often be noticed as delicate 

 dendritic, or tree-like tracery on their surface. I have also noticed 

 the occurrence of Manganese in the ashes of plants, especially those 

 growing on ooHtic soil. 



SILVJER. 



This has before been mentioned as accompanying lead, but it 

 has just been discovered in carboniferous limestone rock for the 

 first time. Some time ago Mr. Pass told me that he had noticed 

 its occurrence, together with gold, in a rock of this formation in 

 one or two places. 



The limestone on which the experiments were made was very 

 pure, so much so as to be used for glass making. The greatest 

 impurity was oxide of iron, about 3 or 4 per cent, of which was 

 determined. It is remarkable that no lead, sulphur or quartz were 

 associated with the silver. 



The following was an analysis of the limestone from a quarry at 

 Walton: — 



Calcic Carbonate 

 Ferric oxide 

 Alumina, &c. 

 Silica ... 

 Silver ... 

 Gold ... 



94.300 

 4.800 



.877 



.020 

 .003 

 trace 



This metal was obtained by cupellation after fluxing with 

 litharge, soda ash, borax, and argol. A very successful method 

 was to dissolve out the lime with Hydrochloric acid, and afterwards 

 treat the washed and dried residue with sodium amalgam. 



The proportion of silver obtained was from 97 to 300 grains per 

 ton. 



