RECRYSTALLIZATION AND AQUEO-IGNEOUS FUSION. 327 
and that such supposed fused material is the source of molten material 
for voleanoes. Mallet supposes that the material is mechanically divided 
so fine that a sufficient amount of heat is developed to fuse the particles. 
However, he does not tell how fine this must be. although he speaks of 
reducing a rock to an absolute powder. What is meant by an absolute 
powder is not apparent, but one might suppose it means a powder the 
particles of which are of molecular size. 
It is apparent that the conclusions of the foregoing paper have an im- 
portant bearing upon the hypothesis of aqueo-igneous fusion. It appears 
that if water is present when the material, as a result of the mechanical 
subdivision or for any other cause, reaches the very moderate temper- 
ature of 180° C., the adjustment is accomplished mainly by recrystalli- 
zation, and that fusion is not necessary to account for the plasticity of 
the rocks. Probably a much higher temperature is required for aqueo- 
igneous fusion than for recrystallization. Barus* has failed to secure 
aqueo-igneous fusion at a temperature of 600° C., and at temperatures 
much lower than this it is certain that recrystallization of the rocks goes 
on very rapidly. 
So far as the typical crystalline schists themselves are concerned, it is 
certain that they are not the products of aqueo-igneous fusion. They 
have peculiar textures characteristic of themselves, which are wholly 
unlike textures of unmodified sedimentary rocks, and unlike those which 
are known invariably to appear in rocks which have crystallized from 
a magma, however the magma has been produced. Hvery magma crys- 
tallizes according to the laws of magmas, and produces textures which 
are characteristic of such crystallization, and these are widely different 
from those of the crystalline schists. 
It does not follow from the foregoing that the deeply buried rocks, in- 
cluding the crystalline schists themselves, may not become modified or 
even fused by contact with igneous intrusives. Indeed, I have held in 
another place that there are all gradations from water solutions to true 
maema;} but in proportion as the condition of the material approaches 
that of a magma, the textures produced approach those of igneous rocks. 
In some regions rocks occur showing remarkable combinations of tex- 
tures characteristic of the clastic rocks, crystalline schists, and the igneous 
rocks. The consideration of such rocks must be deferred for the full 
paper from which the present article is adapted. 
So far as my own observation goes, the phenomena which might be 
called aqueo-igneous fusion are generally local, and in connection with 
great intrusive masses such as batholiths; but in some great areas the 
*C. Barus: 14th Ann. Rept., U. S. Geol. Survey, pt. I, 1893, pp. 161, 162. 
} Principles, cit., pp. 686-688. 
