elxxviii Proceedings of the Asiatic Society of Bengal. [N.S., XV, 
(2) Dharwar sediments and contemporaneous lavas. 
(3) Oldest gneisses re-melted—now post-Dharwar and pro- 
ba ai sears a considerable portion of the “‘ funda- 
(4) Post- Dhatwar aeitbbiaivee: 
(a) Peridotites and ater. ultra-basic rocks. 
(6) Granites and pegmatites 
(c) Epidiorites ated ie and gabbros). 
(d) Elaeolite-syenites. 
These intrusives, especially the granites and xeiated ri acer: 
tities, may belong to more than one period of eruption 
IIT. OR&-DEPOSITION IN THE ARCHAEANS OF INDIA. 
Br ocianeoa ct st fecal cota may now turn to the consideration of 
of Nature . : ore-deposition in the Archaeans of 
d . 
Mining Society some years ago, entitled ‘‘ What is an Ore? 
(Jour., Sibpur C.E. Col. Min. Soc., Vol. ahs p. 39, 1908), 1 
arrived at the following definition of an ore 
‘*A mineral substance containing an cuviaitianlly valu- 
able metal in such quantity that, given a sufficiently large 
deposit of such mineral substance and a favourable situa- 
tion of the deposit as regards transport and corre cen- 
tres, it will pay to work the mineral substanc 
And, ae he psi point of view, I showed eit we could 
rega ard an 
“ es res ay of the concentration by the processes of 
Nature of the originally very sparsely distributed metals, 
into mineral substances fulfilling the conditions as to com- 
position just stated.” 
We will approach our problem from this latter point of 
tinsel of oa iew. Theoretically, any of the Ar- 
posits inthe Archaeans, Chaean geological formations might con- 
tain concentrations of metalliferous mi- 
sone suitable for use as ores; but from the nature of things 
ust leave out of the question the hypothetical oldest 
seisinbea! From theoretical] considerations—which will appear 
later—it seems probable that the re-melted gneisses and granites 
1 The Mysore Geological Department has r enue % o less than 
three successive post-Dharwar granitic intrusives, known respectively as 
the Champion Gneiss, the Peninsular Gneiss, and the younger granites, 
e. The in 
the re-me Said war gneisses io de my division (3). 
