9 
only minerals we can conceive of this nature are those containing 
a large proportion of the heavy metals, such mineral in fact as 
would, when found within reach of man, be considered as metallic 
ores. 
Having thus briefly considered the various zones of the upper 
portions of the earth we are in a position to consider the theory of 
origin of the more important of those primary subsurface concen- 
trations of metallic ores which we call ore deposits, and which 
supply us with all our heavy metals, particularly, so far as we are 
concerned, with gold. 
In the 80’s and 90’s of the last century two rival schools of 
thought as to the origin of these metalliferous ores waged a wordy 
warfare. The rival theories were those of “ lateral secretion ” and 
“ ascension.” The supporters of the former theory urged that 
these metallic ore deposits were precipitates in fissures or other 
cavities from solutions which seeped laterally into them from the 
walls immediately adjacent. That these solutions were aqueous 
solutions of metals derived from the widely distributed but minute 
amount of metals occurring in the surrounding rocks flanking the 
deposit. The bases of this theory were the known and assumed 
movements of water underground and the many determinations 
by Forschamrner and Sandberger of the presence of traces of heavy 
metals in the rocks, and rock forming minerals of mining districts. 
A]) art from the fact that it is just as probable that such traces may 
have been distributed from the vein into the surrounding rocks, 
as that the reverse movement took place, there is considerable 
doubt attaching to several of these determinations, particularly 
with regard to the methods used for the estimation of minute 
amounts of gold, silver, and zinc, many of the determinations of 
these being now looked upon with grave suspicion. 
The supporters of the now generally accepted theory of 
“ ascension ” consider that all the valuable constituents of primary 
ore deposits were brought into their present position in solution 
or as vapours from considerable depths within the zone of fluidity 
or the underlying b ary sphere. Ore deposits are notoriously associ- 
ated with intrusive rocks, which are known to carry much water 
and small amounts of heavy metals. During the consolidation of 
such rocks from fluidity, a chemical process goes on akin to that 
which takes place in the concentration of sea water. Large amounts 
of the most abundant components first crystallise out, leaving 
towards the end of the process a “brine” in which are concen- 
trated the valuable metallic constituents in the form of soluble 
salts and ions in solution in the residual water, which finds its 
way into adjacent and overlying fissures and cavities and often 
by energetic chemical action dissolves spaces in surrounding rocks 
and precipitates in these spaces new minerals partly of economic 
value. 
