APLITE, PEGMATITE, AND TOURMALINE IgI 
matic forms, varying from a fraction to several millimeters in 
cross-section without terminal faces; jet-black in color; and in 
every case examined they are considerably fractured. The 
number of individuals in a group varies greatly, usually from a half 
dozen or thereabouts to several times that number. The width 
of the border zone of the feldspar-quartz areas, or that portion 
of the white mass extending from the outer part of the tourmaline 
ageregate to the junction formed with the gray granite, is also 
variable, but is wider in proportion to the size of aggregate 
occupying the center, and is apparently proportional therefore 
to the intensity of the action controlling the tourmaline forma- 
tion. 
The quartz-feldspar areas are as strongly contrasted in color 
with the light gray granite as are the black tourmalines. The. 
junction between the areas and the granite are entirely sharp and 
distinct, and in no case observed is there any tendency shown 
toward a gradation or merging of color of the white mass into 
the granite. 
A number of thin sections of the feldspar-quartz areas and 
their included tourmaline aggregates were examined microscopi- 
cally. The sections indicated a mosaic of interlocking quartz 
and feldspar, similar in all respects to, and consisting of the 
same feldspar species as the granite. No difference in texture 
and size of the component grains from that of the granite is 
observed. With few exceptions the feldspars were perfectly 
fresh. Cataclastic structure is quite strongly accentuated in the 
feldspar and quartz grains, the cracks are rather wide, and are 
now filled with a colorless, high double refracting mineral. Pri- 
mary muscovite is not present in those slides examined, but 
plentiful small foils of the mineral distributed over the feldspar 
surfaces are seen in places, and from its association must be 
regarded as distinctly secondary. In transmitted light the tour- 
maline is deep brown in color and strongly dichroic. It is 
closely associated with both the quartz and feldspar, filling at_ 
times the interspaces. It is more intimately associated with the 
feldspar, however, and its distribution through some of the large 
