94 TIN DEPOSITS OF NEW SOUTH WALES. 
T do not propose in the present essay to attempt any exact 
delimitation of the boundaries of the different systems of rocks, 
but heer are several points of interest which have come under 
, and which are, I trust, worthy of record although only 
illustrated Page sketch sections. 
ema nama of rocks which are represented in the district 
are as follow 
(a) IcNeous Rocks. 
1. Granite and Greisen, partly metamorphic and partly as 
dykes and bosses 
2. Acidie Igneous Rocks, consisting chiefly of quartz porphyry 
and felspar porphyry (a coarse variety of porpliyrite). 
3. Felspathic volcanic Ash Beds, which are Ag sage associated 
the acidic eruptions last mentioned. 
4, Basaltic streams, which overlie the felapathie ash beds in 
places. 
(6) Seprmentary Rocks. 
Probable Age. Characters of the Rocks. 
SUNLIAN CA ene es Slates, sandstones, quartzites, and conglome- 
rates, which are invariably standing A high 
angles and dipping away from the grani nites. 
Miocene aes alluvial leads or river beds, which are 
in some cases older than the felspathic erup- 
tions, 
Newer Pliocene and Pleis-- Shallow workings and terraces with alluvial 
tocene. tin. 
is one point that will be suggested by a perusal of the 
egias table of formations, viz., that si e granitic eruption 
no sedimentary beds have been deposited in the New England 
area, with the exception of those alluvial deposits which have been 
Jaid down under subzerial conditions; and, since it is pty, gener- 
ally accepted that the granites are of from Devonian to Carbon- 
aferous age (See p. 86, Mines and Mineral i the tableland 
of New England must have been subjected to the ravages of 
atmospheric ‘agents since the close of the Coates period at 
least. 
There is no evidence that, since the granitic upheaval first took 
place, there has been any cessation in the process of denudation, 
and in the period of time which has elapsed the quantity of 
material removed must be truly enormous. 
