he tin ore is invariably found in what Mr. Boyd describes as 
a “whitish cement” which softens readily in water, allowing 
the cassiterite to fall to the bottom of the washing troughs. 
_ Mr. Boyd thinks the character of this formation controls the 
purity of the tin. When it has a yellowish shade he expects 
to find the tin contaminated with arsenic, iron, and bismuth. 
If light gray or white, he notices that the vegetation is stunted, 
but the character of the tin produced is much improved. Ores 
yielding from eighteen to thirty per cent are very abundant, but 
0 not pay to smelt without concentration. Associated with 
the tin ores are found fluor spar, calcite, chaleedony, and topaz. 
old, silver and lead-producing formation. Sometimes a high 
ill or mountain top is seen to be capped with the tin formation. 
Over the entire tin fields prospecting holes have been sunk, 
the bed rock being reached at a depth varying from three to 
ten feet. These shafts have never failed to develop stream tin 
m greater or less quantities. During the wet season, com- 
Mencing in the middle of June, great quantities of rain fall. 
Advantage is taken of the abundance of water to sluice out the 
18 done in a rude way in furnaces built of adobes, yet it is 
Stated that metallic tin can be produced at a cost of two cents 
p : 
i of a man’s head. A curious form resembling small cylin- 
“ts or stalactites is not uncommon. : 
". Boyd estimates the number of veins known at six hun- 
dred, and the number of streams or arroyos yielding stream tin 
