402 = =©. A. Vanhise—Finlargements of Feldspar. 
seen (fig. 1), exactly as quartz enlargements polarize with the 
grains on which they have grown. Further, when plagioclase 
is enlarged, as it frequently is, the new material has twinned 
uniformly with the old, the twinning bands in polarized light 
running continuously across cores and the added borders (fig. 
2). This phenomenon was observed in many different grains 
and in different sections. 
Again, the complex fragments above mentioned as derived 
from a granitic porphyry, and as containing quartz and feld- 
-spar, often have borders of new material and the added por- 
tions resemble, and usually polarize with, the feldspars instead 
of with the quartz, with which they would naturally codrdi- 
nate, if with either, were they composed of silica. Frequently 
the exteriors of this class of grains are apparently all of feld- 
spar, even when a third or more of the edges of the original 
fragments (and in some places for considerable spaces con- 
tinuously) are of quartz (fig. 3). The grain figured consists 
of part of a single, orthoclase individual, including several 
areas of quartz. The secondary enlargement polarizes with 
the feldspar throughout its area. 
* Fig. 4. Jn -polarized light; x 100. Part of section of Eagle Harbor sandstone, 
re hoclase fi oken and re-cemented b. naary 
material crystallographically continuous with the original fragment and with 
the border of newly deposited material. | 
of new material. ese basic grains are often very feldspathic, 
Here an en- 
largement instead of being a unit, as it commonly is in the rhe 
cedi duals e 
feldspars at the edge of the nucleus have ordinarily controlled 
