210 TRANSACTIONS OF THE [Apr. 24 
In other cases the different areas of quartz in the feldspar are 
wholly independent of each other, producing the structure to 
which the term micropoikilitic* has been applied. 
Beyond the development of microperthite and a varying 
amount of cloudiness, the feldspar, as a rule, shows no decided 
alteration. Muscovite and chlorite have been rarely produced 
at the expense of feldspar, but not in sufficient quantity to exert 
any influence upon the character of the rock. 
Like the quartz, the feldspars show much evidence of 
mechanical strains. Undulatory extinction is quite general, 
often accompanied by granulation, either peripheral or extend- 
ing through entire individuals. In the plagioclase there is 
much bending and breaking of twin lamelle, while the develop- 
ment of twinning by pressure is often seen. 
In the normal granite, biotite is the only ferro-magnesian 
mineral, and varies greatly in quantity, often being entirely 
absent. It is dark brown, strongly pleochroic, and fairly fresh 
as a rule, though sometimes bleached. Pleochroic halos are 
abundant, often extending through an entire fragment of the 
mineral, and showing no dependence upon inclusions. Besides 
the original biotite the very basic phases of the granite contain 
small amounts of biotite that is clearly of secondary origin. 
The distribution of hornblende in the granite is very limited 
being confined to the basic segregations which have the com- 
position of diorite. In these, hornblende is the prevailing 
ferromagnesian mineral, It never shows any decided crystal 
outline, though occasionally in the form of an imperfect prism. 
It is dark green, strongly pleochroic and usually very fresh.. 
In one section it is associated with a considerable amount of 
light green monoclinic pyroxene. A parellel growth with 
biotite is common. 
Tourmaline characterizes, by its presence in considerable 
quantities, a few limited areas of granite. It occurs in the ordi- 
nary prism with triangular cross section, or in irregular masses. 
The color is brown or green, sometimes in zonal arrangement, 
and the pleochroism intense. 
The ordinary minor constituents of granite, such as apatite, 
zircon, ilmenite, leucoxene, etc., are present in varying quanti- 
ties, but need not be described. 
The granite shows several phases which differ considerably 
from the normal type of the rock. Coarse pegmatitic varieties 
are abundant, both associated with the ordinary rock and form- 
ing independent masses. In the latter tourmaline is sometimes 
__ * Williams, I. H.. “On the Use of the Terms Poikilitic and Micropoikilitic in 
Petrography,” Journal of Geology, I., p. 176, 
