136 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
irregular grains occurs sparingly, associated with the dark silicates. 
Passing over the crest of Wampatuck Hill to the most easterly 
of “ The Broken Hills,” the typical “ bluish quartz porphyry ” appears 
without trace of flow structure. Macroscopically there is a com¬ 
pact grayish blue ground mass with numerous irregularly arranged, 
well-banded phenocrysts of flesh-colored orthoclase, from one or two 
up to five mm. in length, with more or less equally abundant glassy 
smoky quartz grains scattered among them. Miss Bascom (’96, 
Plate 7,) figures a specimen from the South Mountain, Penn., 
locality, identical, except in color, with specimens from Pine Hill. 
Microscopically, this ground mass is granophyric and largely 
isotropic with characteristic interlacing lath-shaped feldspars, 
arranged in fluidal texture following the outlines of the phenocrysts; 
in part, also, it is glassy. Into this ground mass are packed large 
quartz and feldspar phenocrysts. The quartz is idiomorphic and 
not fractured; it shows beautiful embayments of the ground mass. 
The boundaries are sharply outlined, and the hexagonal sections are 
frequently prominent. Some sections show marked distortion. 
The feldspar is practically all monoclinic and is microperthitic in 
nearly all cases, showing a very thorough interpenetration. In some 
cases the feldspars have so many inclusions as to appear like those 
of a gabbro or anorthosite (Smyth, ’95, p. 272). 
The feldspar is usually in rectangular crystals, having rounded 
corners with outlines more or less exactly defined, and in some phases 
once twinned. A little triclinic feldspar occurs in a few sections. 
Hornblende forms irregularly rounded and fractured grains and 
particles scattered through the rock, as well as occurring plentifully 
in needles through the ground mass and scattered parallel to the 
margins in the large feldspars. A variety of decomposed dark 
silicates also appears both in the ground mass and in the feldspars, 
especially along the edges of the feldspars. Magnetite and a limon- 
ite decomposition product occur sparingly. Hematite forms red 
specks in some slides. Titanite in transparent crystals is abundant 
in some sections. Sillimanite in long crystals is also present. In 
places the rock is brecciated with black fragments of 1 cm. to several 
cm. in diameter, which are clearly outlined, but inseparable from the 
porphyry. Although so distinct in the field, and in fineness of 
texture in the section, the components are the same as those of the 
ground mass of the remainder of the rock. It is apparently without 
phenocrysts, but approaches in places a microgranitic texture. 
