326 VAN HISE—METAMORPHISM OF ROCKS AND ROCK FLOWAGE. 
deformed by true flowage of the matrix and by slipping or shearing 
readjustment of the granules. So far as the average mass deformation 
is concerned, the result is substantially the same as though each rigid 
granule had not acted as a unit. Indeed, the same average mass de- 
formation may be accomplished wholly by granulation and welding, 
as in Adams’ experiments (see page 310); but it may, perhaps, be 
doubted whether this is ever strictly the case with rocks in nature, for 
some small amount of water is always present, and probably, even in 
the cases of apparent perfect granulation, some degree of solution and 
recrystallization from solution has occurred. In the case of the imper- 
fect crystalline schists, which are very widespread rocks, the adjustment 
to the new form is accomplished in part by the process of differential 
movement of rigid granules and in part by solution and redeposition. 
It is only in the case of the typical granulated rocks that we can sup- 
pose that the process of deformation is mainly accomplished by the 
movement of the solid particles over one another, and it is only in the 
perfect crystalline schists that we can suppose that the deformation is — 
accomplished almost wholly by recrystallization. 
Nothing ig said by the foregoing conclusions as to the condition of 
the material below the zone of the crystalline schists or the meaning of 
the flowage of such material. 
The conclusions of the foregoing pages show clearly the meaning of 
rock cleavage. I have already held that this structure is largely due to 
the similar crystallographic orientation of numerous mineral particles, 
and especially those which are authigenic,* and therefore that rock 
cleavage is a capacity to part largely due to the actual cleavage of the 
similarly oriented mineral particles. As the cleavage of mineral parti- 
cles has long been known to be a molecular structure, it follows that the 
cleavage of rocks is also largely a molecular structure. I have also ex- 
plained that the similar crystallographic orientation is frequently, per- 
haps usually, accompanied by an arrangement of the mineral particles 
with their longer diameters in the same plane as the cleavage, and that 
this dimensional arrangement is a factor in rock cleavage, although one 
of probably less importance in most cases than that of the erystallo- 
graphic orientation of the mineral particles. 
RECRYSTALLIZATION AND AQUEO-IGNEOUS FUSION 
It has been held by Mallet} and by others that the interior-motions 
of mass dynamic action are sufficient to produce aqueo-igneous fusion, 
* Loc. cit., pp. 633, 635. 
+ Voleanic energy ; an attempt to develop its true and cosmical relations, by Robert Mallet: Phil. 
Trans. Roy. Soc., London, vol. 163, 1873, pp. 147-227. 
