304 VAN HISE—METAMORPHISM OF ROCKS AND ROCK FLOWAGE. 
particles show marked strain-shadows. In still other cases the strain- 
shadows are accompanied by more or less of granulation, and this 
phase of the rocks grades into the ordinary granulated rocks. Thus 
there are all gradations between molecular readjustment or recrystal- 
lization almost part passu with deformation, and readjustment almost 
wholly by granulation. 
HKvidence that recrystallization does nearly keep pace with deforma- 
tion in the case of the crystalline schists consists partly in the absence 
of marked strain structures, for it is to be supposed that if recrystallization 
did not nearly keep pace with deformation the result would be that the 
mineral particles would show important strain-shadows or even granu- 
lation. The texture characteristic of the crystalline schists (described. 
pages 297-299) is itself further evidence for continuous recrystallization 
by solution during deformation. Itisatexture peculiar to the crystalline 
schists. Ifthe minerals were not readjusted in a continuous fashion they 
must have become granulated by the mechanical forces. If they had 
become fused into a magma, from that state the material would recrys- 
tallize with textures peculiar to the igneous rocks. The regular arrange- 
ment of the mineral particles with their longer axes or definite planes 
at right angles to the direction of greatest pressure is just what would 
be expected if the contained water is everywhere taking material into 
solution at the points of great strain, and adding this material at the 
edges of the particles, and thus continuously building them out laterally. 
Further evidence that recrystallization nearly keeps pace with defor- 
mation is found in the porphyritic minerals which frequently occur in 
the crystalline schists. Some of the more common of these porphyritic 
minerals mentioned (page 292) are garnet, staurolite, andalusite, feld- 
spar, hornblende, chloritoid, chlorite.and mica. Such porphyritic min- 
erals ordinarily show no perceptible strain. They frequently lie with 
their longer axes or readiest cleavage across the schistosity. This is 
true even of mica and chloritoid, the cleavage of the porphyritic con- 
stituents cutting directly across the cleavage of the abundant small in- 
dividuals of mica which accord with the schistosity. It has been main- 
tained (page 292) that such porphyritic minerals have developed under 
static conditions after mass movement has ceased. ‘These porphyritic 
minerals seem to be evidence that the differential stresses of static con- 
ditions are ordinarily not sufficient to control the orientation of the min- 
eral particles; that in order to do this the differential stress must be 
sufficient to produce actual movement throughout the mass of the rocks. 
If this be so, we must suppose that the orientation of the minerals produc- 
ing schistosity occurred during the movement itself, or, in other words, 
that recrystallization nearly kept pace with the movements. 
