324 VAN HISE—METAMORPHISM OF ROCKS AND ROCK FLOWAGE. 
rial may have slightly different compositions, and this be discovered by 
a difference in the color, refraction, extinction, or in some other way. 
Finally, all of the old mineral particles may be regenerated or recrys- 
tallized. 
Therefore a given portion of a definite mineral particle in a crystalline 
schist may not have been recrystallized at all, or, on the other hand, may 
have recrystallized several or many times. It is believed that ordinarily 
the recrystallization is far advanced or complete for all parts of a typical 
schist, although this is far from the case in the semicrystalline schists or 
imperfectly schistose rocks. 
Of course, in this rearrangement it is not supposed that the identical 
molecules which are taken from the more severely stressed parts of a 
grain are necessarily deposited at the places of less stress upon the grain. 
Undoubtedly there is great interchange of material between the particles 
by means of the solutions. Itis, however, thought probable that in many 
cases of deep-seated deformation, where the passage of solutions is diffi- - 
cult and slow, that much of the identical material which is taken from a 
grain at one place is added to it at another place. 
When new individuals are produced in any way,-as by granulation 
or by the deposition of new mineral particles, perhaps as different species 
from any originally in the rock, they are subject to the same laws as the 
original mineral particles. Many have a tendency to form with similar 
crystallographic orientation. However, it is only rarely that the orien- 
tation of the particles of a given mineral approximates exactness. One 
mineral—for instance, mica—may be well oriented, whereas such min- 
erals as quartz or calcite may not be oriented. 
In proportion as the minerals readily respond to the forces of recrys- 
tallization or are mobile, they do not gain or retain regularity of ar- 
rangement. After mass movement has ceased the temperature may be 
sufficiently high and the heat be held for a sufficient time, so that the 
solutions may completely recrystallize the minerals under mass static 
conditions, and therefore orientation may be lost. In proportion as 
minerals do not readily recrystallize or stubbornly resist the force of 
recrystallization, the minerals once oriented retain their regularity of 
arrangement. 
The most mobile of the important minerals is calcite. Quartz is also 
somewhat mobile. Therefore these minerals in marble and in recrys- 
tallized quartzite frequently lack regularity of arrangement. However, 
in some cases even calcite may show well developed, similar crystallo- 
graphic orientation. The usual almost complete lack of regularity for 
calcite is illustrated by most of the marbles from the Laurentide moun- 
tains to Alabama. The complete recrystallization of quartz to a coarse 
