— 
1871. J i] [ Dutton. 
under ordinary temperatures to which water is subjected, are in no re- 
spect changed, may be completely altered by water confined in strong 
s. Silicates, aluminates and calcareous 
matters in the amorphous condition, may not only be made crystalline, 
vessels and heated to dull redne 
but their degrees of hydration may also be permanently altered; and he 
also mentions the production of anthracite by a simi 
ir process, from wood. 
Indeed, the changes both of structure and chemical constitution, which 
may be produced in this manner, are very great, and extend, in all proba- 
bility, to nearly the whole range of mineral matters found in the rocks. 
Now, if as is generally believed and accepted, these are the changes in 
progress, while rocks are undergoing metamorphism, then, in all proba- 
bility, the rocks are undergoing at the same time «@ change tn their specific 
gravity. Itis highly probable, if water is the chief reagent, and if it 
constitutes a change both chemical and physical, that the specific gravity 
of the mass, into which it enters, is not the same as it was before such a 
change took place. Butif we admit this, then we have also admitted 
that the volume of those rocks has either increased or diminished. If we 
assume it to have increased, there must take place an expansion, and such 
an expansion must necessarily be upward. For, beginning at the lowest 
level, at which any such change may be assumed to supervene, the total 
weight of the superincumbent mass is the same as it was before, and 
hence there would be no change at that level. Nor could there be lateral 
expansion of any importance; all expansion would of necessity be verti- 
cally upwards. On the other hand, a decrease of volume would occasion 
a subsidence for converse reasons. 
If we were to assume a change in the specific gravity of 1000 fect of 
rock, to the extent of five per cent., we could account for a change of 
level of 50 feet, and a series of rocks as thick as the carboniferous in this 
State, would, with an equal amount of change, give an alteration of level 
equal to the average attitude of the North American Continent above 
the ocean. It is, of course, impossible to conjecture the depth to which 
metamorphic action may extend, though it is undoubtedly very great; at 
least eight or ten miles, and there might be no great improbability in 
supposing such changes to take place through a large portion of that 
depth at the same time. 
That the rocks far down below the surface take up under the influence 
of great pressure, aided no doubt by heat, large quantities of water, car- 
bonic acid, sulphydric acid, and perhaps other electro-negative agents, is 
manifest inthe materials issuing from voleanoes and from thermal springs. 
Water and gaseous acids issue in such enormous quantities from volea- 
noes, as to constitute a large fraction of the entire mass delivered, indi- 
eating that the solid materials have become super-saturated with them, 
and the association is resolved as soon as they reach the surface of the 
earth, and are relieved of the pressure to which they have been subjected. 
The overflow of volcanoes would, it is suggested, be susceptible of a 
similar explanation. Let us suppose a stratum ortwo, situated afew miles 
