MEANING OF ROCK FLOWAGE. RUB 
During the process of recrystallization, at any given moment there 
will be the greatest shortening in the direction of greatest stress, greatest 
addition in the direction of least stress, and there may be shortening or 
addition in the direction of mean stress. Consequently the shape of the 
modified particle may be that which 
would be produced if a plastic grain 
were rolled out, the sides being confined 
in one direction, but with liberty to Cc 
elongate in another direction; or it may 
be that which would be produced if a 
roundish cake of dough were pressed fraune2.—Possible relations of old and new 
between two boards, and consequently RLS Gi ACER ISIE eee 
elongated in all directions at right angles to the direction of greatest 
pressure; or, finally. the mean stress may approach so closely to the 
maximum stress that there is shortening in two directions and elongation 
in a single one only, in which case a fibrous structure is produced. How- 
ever, from my study of the crystalline schists I am inclined to believe 
that shortening in one direction and unequal elongation in the directions 
at right angles to this is the most common case, though my thin sections 
give illustrations of all the cases. 
In some cases the direction of greatest pressure varies within exceed- 
ingly short distances. The most common case of this is caused by the 
existence of large rigid particles, such as feldspar, garnet, or some other 
refractory mineral, which act as transmitters of pressure and deliver the 
stress nearly normal to themselves. In such cases the direction of 
ereatest pressure adjacent to the rigid mineral particles is modified from 
point to point. The new particles there forming may curve about the 
rigid granules. Thisis beautifully illustrated by the flat, curved quartzes 
adjacent to feldspar in the quartz-porphyry described by Futterer (plate 
19, figure 1, see page 301). In such a case the direction of orientation 
for the quartz, in order to adjust itself to the pressure, would continu- 
ously vary, and the flat individuals might show undulatory extinction 
as originally developed without having been strained subsequently. 
What is true of one mineral particle is true of all others, and there- 
fore we conclude that, while recrystallization is constantly occurring in 
the deformation of rocks, at any time the majority of the mineral parti- 
cles retain their integrity and are nuclei which at any moment orient the 
material being deposited. In many crystalline schists evidence may be 
seen that this has happened. The old mineral particles, represented by 
the cores, may have been slightly altered, and in consequence of this 
may be discriminated from the freshly added material, or the cores may 
show a border of iron oxide or other mineral, or the old and new mate- 
