178 2'he American Geoloyisl. March, 1897 
of water whicli the magma can retain is insufficient to offset 
the loss of heat due to the vaporization of water. It is clear, 
however, that with increased pressure solutions might be hot- 
ter and fusions more highly h3'^drated; and we see ro reason 
to doubt that at moderate depths in the earth heat and water 
may exist in equal and perfect cooperation. Whether at great- 
er depths igneous fusion prevails must depend, of course, upon 
the temperature and its relations to the elevation of the fus- 
ing point by increase of pressure. The absorption of M'ater 
under pressure by a liquid magma appears to be a chemical 
process, a true hydration, the water disappearing as such. If 
this view be correct, there is certainly some reason to think 
that we have here a reinforcement of Daubree's explanation of 
the downward progress of water in the earth's crust. It is 
not only urged down by capillary attraction, but also, as pre- 
viously stated, to make good the loss due to its absorption by 
deep-seated magmas. 
Pressure promotes aqueous absorption and solution, but re- 
tards fusion by raising the fusing point. High temperatures, 
on the other hand, favor fusion, of course, but are antagonis- 
tic to aqueous absorption, and hence to solution. If, as we 
must believe, the pressure increases more rapidly at great 
depths than the temperature, it may well be as has been clear- 
ly shown by others, that purely igneous fusion nf)where ob- 
tains, but the molten magmas at the greatest as well as at 
moderate depths are in a state of aqueo-igneous fusion. It is 
a necessary corollary to this view that as refrigeration pro- 
gresses and water is, in consequence, more abundantly absorb- 
ed, the degree of liquefaction at a given depth increases until 
heat and water are in perfect cooperation, and then declines 
with farther loss of heat, since it is manifestly impossible 
that sufficient water should be absorbed at any depth to give 
a general liquid zone by approximately pure solution. It is 
probable, therefore, that the continuity of fusion and solution 
is most fully realized during the differential solidification of 
a body of magma: and pegmatite is, in a truer sense than 
any other lithologic type, the connecting link between igneous 
and aqueous rocks. 
Strictly speaking, nearly all, if not quite all, known rocks 
are secondary. This is generally conceded for the sedimen- 
