THE FORMATION OF DEPOSITS 23 
water being superheated would be a powerful solvent, and 
would thus obtain alkalis, that increase its power of dissolving 
quartz and metallic sulphides. The metallic barysphere, 
like the iron meteorites, doubtless contains sulphides, such as 
the iron sulphide, troilite, and phosphides (e.g. schreibersite), 
and carbon as graphite. The solution of troilite would give 
rise to ferrous sulphate, which is a solvent for gold. The 
water would also include chlorides, and fluoric and boric 
acids. This complex solvent would work its way upwards 
through the rocks, dissolving from them silica and metallic 
sulphides. The small spaces would unite into large channels 
along major fissures and fault planes, and through them solu- 
tions would rise more quickly. From the lower zone of 
solution the water would reach conditions under which it 
would begin deposition. It would be constantly passing 
under less pressure and lower temperature, and both in- 
fluences would throw materials out of solution. Chemical 
reactions would aid, as contact with lime would neutralize 
acid solutions, while carbon by reducing the ferrous sulphate 
solution would precipitate metallic sulphides; and as gold 
would no longer be soluble it would be precipitated at the 
same time. Hence solutions rising up fissures, and especially 
up the great faults which mountain structures show to ex- 
tend over 100 miles deep, would bring to the surface metals 
from the ore-zone. 
Macwmatic OREs—The nature of these solutions is the main 
current problem in ore genesis. As the solvent must be 
mostly water and the temperature high, they are justly 
called hydrothermal ; but as many authorities held that all 
the water on or in the earth’s crust falls upon it as rain, the 
ore-forming solutions were attributed to surface water which 
had sunk underground, had there dissolved scattered metallic 
particles and deposited them in lodes as the water was forced 
to the surface by the gas pressure due to heat. Ores formed 
by this process of lateral secretion appear to be more abun- 
dant than has been generally admitted in recent years; they 
include not only ores of iron and manganese, but many 
others, such as the copper ores of Mansfeld, of Cheshire, and 
some of those of Katanga, some of the lead and zinc ores of 
Mississippi and the rich gold ores of Mount Morgan. 
For ordinary lodes the lateral secretion theory has been