FORMATION OF MINERALS, CLAYS, ETC* 
42 7 
become coal, silica takes the place of some of the organic 
matter; the sulphur and phosphorus, set free from animal 
matter, enter into new combinations; the mass in drying 
contracts irregularly, and is full of cracks and fissures, and 
in these water circulates, being forced through at a tem¬ 
perature corresponding to the depth. As it circulates, it 
carries with it, from place to place, various minerals; re¬ 
moving them from one point and leaving them behind at 
others, according to the nature of the chemical operations 
going on. 
W O 
After a time the beds sink lower, the clays become subject 
to greater pressure, the limestones get compact and pass 
into marble ; the metals combined with oxygen or sulphur 
group themselves together in cavities with other minerals 
earthy and crystalline. 
One step more—elevation begins. The clays are now 
subjected to the pressure from below as well as above, and 
under this double squeeze they become twisted and bent like 
pieces of cloth, and they also assume a new lamination. 
They become slates. Some of the sandstones have become 
by this time converted into quartzite, and the limestone has 
completed its crystallization. When elevation comes these 
hard beds, being brittle, are broken, leaving large open spaces 
and great cavities beneath the surface. Here also water 
collects. 
Yet again. Far down, at a depth of tens of thousands of 
yards, and therefore under great pressure, water, in com¬ 
pany with the minerals which form granite, accumulates in a 
mixed mass, and a slow but incessant crystallization goes on 
amongst them, in which the water is entangled with the 
other minerals, and helps to form a part of the substance of 
each crystal. 
But in all this there is no melting such as we have in 
volcanic rocks. In these latter water is not present in the 
same way; they were formed much nearer the surface ; and 
they belong to a different class of phenomena. Their origin 
is detected by the absence of water in them. 
Wherever great change has taken place at great depth— 
wherever is seen the rich variety of minerals and the valuable 
supply of metals,—there water has acted. 
Water carried down in the rocks that descend is worked 
up into new forms, and is only returned to the surface when 
it has done its work and when other supplies from above 
have replaced it. 
And in time the rocks thus elaborated rise again—some at 
small depth will have been little altered, and with their 
