10 
MUSEUM BULLETIN NO. 2. 
erals in micropegmatite, in which the feldspars contain oriented 
inclusions of quartz. Masses of pure quartz are very abundant 
and in some cases hold needles of fibrous hornblende. This acid 
phase strongly resembles in composition the granite (micropeg- 
matite) described below, although it is coarser in texture, holds no 
biotite, and is richer in plagioclase. The similarity between the 
acid bands and the granite (micropegmatite) suggests that they 
have had the same origin. 
The basic phase of the pegmatoid gabbro consists of long 
needles of hornblende with some interstitial quartz and feldspar. 
Under the microscope it is seen that the apparent order of 
crystallization is the reverse of that of the hypersthene gabbro 
which has an ophitic texture. In the pegmatoid variety, the 
hornblende, which is here compact and evidently primary, 
tends to idiomorphic outlines against the andesine, the other 
essential constituent. A little orthoclase and calcite are the 
accessory constituents, while the secondary minerals consist 
of epidote and calcite. The contact between the two phases 
of the pegmatoid gabbro is generally gradational, but has been 
observed to be quite sharp, like an igneous contact. 
In one instance a dyke of aplite was found, which distinctly 
cut the basic gabbro, but was confined to the sill and apparently 
occurred near the upper contact of the sill. Microscopically, 
the essential constituents of the aplite are quartz and micro- 
pegmatite in which the quartz of the latter contains oriented 
inclusions of orthoclase. The latter mineral is usually clouded 
with a great number of sericite particles. The fibrous horn- 
blende which is present, exhibits the pleochroism, c, bluish 
green, b, strong green, a, yellowish green, and thus resembles 
the secondary hornblende described above. 
In the interior of the basic sills, there occurs a granitic phase 
in irregular masses with gradational boundaries with the sur- 
rounding gabbro. This phase consists of long needles of horn- 
blende enclosed in a ground-mass of micropegmatite. The 
microscope shows that this hornblende is identical in optical 
and physical properties with the secondary hornblende described 
above, but in this case, transformation of the augite into horn- 
blende is complete. The hornblende has a distinctly shredded 
