106 TIN DEPOSITS OF NEW SOUTH WALES. 
Although this lead of tin is small and has no immediate 
onomic value, its occurrence is of great importance as furnish- 
ing evidence of the possible widespread occurrence of leads below 
some of these acidic volcanic rocks, more especially when it is 
considered that there are very widespread areas of these rocks, 
below some at least of which tin leads may yet be found. 
T have devoted a good deal of space to a description of Bailey’s 
mine in this essay, not because it is the only alluvial mine in the 
district, but on account of its value and the many interesting 
features which can be elucidated there. 
? 
present time, although they lie below the basalt and are subject 
to all the disadvantages of deep sinking, they do not appear to 
be sufficiently thick to pay. At the Brickwood claim the wash 1s 
load is not, I am informed, payable. 
Rewations or Icyrous Covertna Rocks. 
It will be apparent that a great deal of interest attaches to the 
period of the different eruptions of the igneous rocks of the dis- 
trict, apart from the economic aspect of the question, which is 
intimately associated with the period at which the deposits of 
alluvial tin commenced to be formed. 
With regard to the formation of the tin-leads, it will be well to 
the granites or as veins of segregation, and in both cases the 
tin was probably introduced into the rock contemporaneously 
with the formation (metamorphism) of the rock itself. Whether 
it originally existed as a fluoride of tin, and has since been con- 
verted into oxide, the numerous fluorides which are associated 
times, since all granite having been formed at gr 
