8 
now languishing gold industry, an outline of the main principles 
concerned in the formation of ore deposits, particularly of gold 
deposits. 
I have already indicated to you the widely scattered nature 
of our original elemental supplies and their low concentration, 
with very few exceptions, in the great mass of the earth’s crust. 
Wliat are the nature and origin of the concentrations upon which 
we must depend for our industrial supplies ? Of the three com- 
ponents of the outer accessible portion of the earth, the atmosphere 
will yield us only oxygen, nitrogen and water amongst all the many 
elements and simple compounds we require. The second great 
crustal division, the ocean and lakes, or hydrosphere, now yield 
and will continue to yield us, in addition to water, sodium and 
chlorine, and possibly in the future potassium, which it contains 
to the extent of four parts in ton thousand. It is evident that it is 
on the lithosphere, or solid crust of the earth, that the chemist is, 
and will be, dependent for most of his material, whether he is en- 
gaged upon purely scientific investigations or on industrial manu- 
facture. To appreciate the facts and problems of ore deposition 
some knowledge of the earth’s crust is essential. 
The model’ll geologist has used a chemical basis for his division 
of the lithosphere into several concentric zones and belts. The 
upper zone or zone of katamorphism. is characterised by exothermal 
reactions and by the preponderating formation of simple compounds 
from more complex ones. It is divided into two “belts,” the 
upper “ belt of weathering ” in which aqueous solution, oxidation 
and carbonation are the most prominent features .* the lower “belt 
of cementation ” in which hydration of pre-existing compounds 
and filling of spaces by deposition from solution are predominant. 
At a depth of approximately 10,000 metres begins the second 
great zone of the lithosphere, the “ zone of anamorphism,” char- 
acterised by the predominance of endothermal reactions, particu- 
larly silication and dehydration, and by the building up of complex 
molecules from simpler ones. Under the enormous pressure exist- 
ing at this depth all known mineral masses are plastic, and therefore 
cavities, other than sub cap illary ones, must be absent. 
l^eneath the zone of anamorphism and at times bursting through 
both this and the overlying zones, is the zone of actual or potential 
fluidity, actual probably only under local conditions of reduced 
pressure. 
Beneath this again is the “ barysphere. ” The average density 
of the whole earth as determined by astronomical methods is f>-6, 
whilst the average density of the lit hosphere, i+e. f the top 10 miles 
of the solid crust, is given by competent authorities at 2-7. We 
must therefore assume that below the lithosphere there is a bary- 
sphere, i. e . , a mass of minerals with high specific gravity. The 
