29 
ECONOMIC GEOLOGY 
mountain folding. The material of the ore-zone and bary- 
sphere may be regarded as igneous in the sense that they are 
holocrystalline and are formed of minerals that consolidated 
under high temperatures and pressures ; but metallic ores 
do not appear to be primary constituents of the ordinary 
igneous rocks of the earth's crust. Even the deepest seated 
plutonic rocks have received the metals in their lodes—except 
such as iron, manganese, and aluminium— rom an underlying 
layer. 
PLuTtonic, JUVENILE, AND MAGMATIC WaTERS—The normal 
influence of igneous rocks in ore formation is indirect. Their 
intrusion produces fractures and fissures along which solu- 
tions can pass, and they raise the temperature so that the 
gas pressure forces the water upward. The main intro- 
duction of metals into the upper layers in the lithosphere, 
in addition to its normal constituents, is by the ascent of 
deep-seated water. This water is known as plutonic from 
its deep origin, or as magmatic after its derivation from 
igneous magmas, or as Juvenile (Suess) since it is making 
its first appearance on the earth's surface. 
A large quantity of this water is constantly arising from the 
interior (cf. Chap. XIX, Pp. 220-2). It must begin its ascent 
through minute spaces. The liquid cavities in quartz often 
occur in lines passing from one crystal to the next, showing 
that the entrance of the liquid was after the consolidation of 
the quartz. This movement must be very slow. At depths 
of 6 to 12 miles the temperature is probably above 687° F,, 
the critical point of water, which at it can exist only as 
steam. Below 30 or 40 miles, the temperature would be 
above 3600°F., and water would be dissociated into its 
constituent gases, which could combine only in a zone cooler 
than their dissociation point. Water after its formation 
would gradually work its way upward into a zone where 
fissures and cracks would enable it to ascend more freely, 
That fractures happen at great depths in the crust is shown 
by the evidence of earthquakes which result from deep- 
seated disruptions. Ruptured rock surfaces at great depths 
would remain in close contact, but not too close for the passage 
of films of superheated water. Ruptures must occur below 
the level where plutonic water begins its ascent in innumerable 
tiny trickles through thin spaces or scattered pores. This