TIN DEPOSITS OF NEW SOUTH WALES. 107 ¢ 
The evidence adduced from Bailey’s mine shows us that tin- 
leads were in course of formation during the acidic eruptions, and 
that, in some cases at least, tin-leads may be overlain by felspar 
porphyries, but the nature of the rock itself will preclude the 
Mii 
(1.) That any widespread surface floes of these rocks could 
occur, because they are necessarily of too vi a nature 
to flow far from their vent, and therefore 
(2.) That tin leads could not be buried up by them unless 
the rocks had been inverted during a series of eruptions, 
as with the domites shown by Professor Judd in his 
work on volcanoes. 
WHat consTiTuTES PAayaBLe TIN. 
a. In lodes. 
b. In alluvial. 
It is a somewhat difficult thing to state with authority what 
proportion of tin will pay for extraction in a country like this, 
where the facilities for working vary so greatly in different local- 
ities, and I shall content myself with giving a few illustrations of 
what is considered payable. 
irst, as regards lodes, and in this category I would include 
those irregular deposits to which I have alluded, but which have 
to be crushed in the same manner as true lodes. 
At Butler’s lode, which is situated about 16 miles from Emma- 
_ ville, over a very rough track, 5 per cent. of black tin is con- 
sidered payable, a battery, driven by steam, being erected on the 
