METAMOEPHISM. 
49 
been filled witfi calc spar. So tlie loose sands bave been 
cemented and compacted into sandstone_, and that again into 
quartz. The clays have become shales and slates. All together 
have become granite. But in what way has this been done ? 
What is the great agent of metamorphorsis in the earth ? We 
have yet to consider this question. 
A very superficial glance at the economy of nature in carry- 
ing’ on the daily routine of operations on om’ globe will satisfy 
any one that the circulation of water^ from the ocean and through 
the atmosphere^ upon and beneath the surface of the land_, and 
so back again to the sea_, is in the highest degree important. 
And the more the phenomena of water are studied the more 
important do they appear. ISTot only does the water in its cir- 
culation modify the main features of the surface_, but a large 
part enters beneath the surface and emerges only after having* 
travelled far and penetrated deep. In its journey through 
strata and among the deep recesses of the earth it performs 
work that most of us dream but little of. Distilled from the 
ocean as warm vapour_, the atmosphere becomes saturated and 
either as invisible vapour or cloud the water is drifted along 
for hundreds of miles with little change. But no sooner is it 
converted into rain and passes through the lower strata of the 
atmosphere to the earth_, than it absorbs carbonic acid and a 
few other ingredients. With these powerful but simple im- 
plements it soon works wonders. It dissolves a way for itself 
where it cannot run through porous rocks back to the surface,, 
it makes its way downwards,, now removing from^ now adding 
to the strata or the fissures through which it passes. As it 
goes down it acquires the temperature of the earth^s interior 
— a temperature increasing gradually with the depth to 
the greatest depths hitherto reached,, but nowhere becoming’ 
excessive. The warmer water is with respect to some 
minerals a stronger,, with respect to others a weaker,, solvent. 
The water makes its way silently^ but as it goes it everywhere 
promotes change. Some rocks it cements^ others it loosens ; 
in some the minerals and fossils are altered in material,, but not 
in form ; while in others the form is altogether obliterated^ but 
the material remains. Down to the greatest depths it is con- 
veyedj not rapidly perhaps^ but with a certain inevitable inexo- 
rable fate. Up from these depths it re-ascends^ governed by the 
same fate. While some water sinks,, an almost equal quantity 
is evaporated again^ and the water from below is constantly 
sucked up to replace that which is taken from the surface. 
This great law of nature is as certain and inevitable as the 
circulation of the blood in a living human being. It represents 
the life of the world. 
And this it is that promotes metamorphism. Uo sooner 
VOL. IV. NO. XIII. E 
