140 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
brilliant grains of smoky quartz, and which is brecciated with larger, 
fractured white feldspathic fragments of well-marked outlines, 1.5 cm. 
or more in diameter, giving in the field somewhat the appearance of 
an ash-bed rock. Upon weathered surfaces it exhibits a coarse 
fluidal texture. Under high magnification it shows an extremely fine 
microgranitic ground mass composed of minute lath-shaped feldspars, 
regularly bounded quartz grains, various green, altered silicates, 
rectangular magnetite particles, and scattered hematites. The 
phenocrysts, which make up perhaps a third of the rock, are also 
small, mostly under 2 mm. long. Quartz is the most abundant; it 
seems to be younger than the feldspar, crystals of which are 
included in its own well-marked crystals. The feldspar crystals are 
not so perfect as in the types previously described, but show hand¬ 
some Carlsbad twins and contain hornblende needles. Biotite occurs 
throughout. It is of various shades from pale green to ultramarine. 
Flow texture in the arrangement of the ground mass is apparent, 
although not strongly marked. 
Melaphyr. — The melaphyr upon Hough’s Neck has been petro- 
graphically treated of by Professor Wolff (’82), hence detailed men¬ 
tion of it here is unnecessary. Professor Wolff has shown that its 
true character is that of an altered basalt. In fact, except in regard 
to its amygdules, most of the rock is clearly a diabase or olivine-free 
basalt; the olivine being very rarely evident. For the most part it 
is compactly or imperfectly crystalline and rather soft. Its color 
varies, according to the condition of the iron oxide, from dull grayish 
green to dull reddish or purplish tints,—the former tint being 
characteristic of the base of the Hough’s Neck How, the latter of 
the top of the flow. The same variation has been noted by 
Professor Crosby (’94, p. 242) in the case of the Huit’s Cove area 
in Hingham. In the brown melaphyr at the top of the Hough’s 
Neck flow, amygdules are conspicuous. They consist chiefly of 
calcite, which is readily cleavable and has been very frequently 
removed on the surface, through solution by acidic infiltrations, 
leaving the original steam cavities intact. Epidote and quartz also 
occur, as well as chlorite and feldspars, as secondary fillings of 
these cavities. Barely the superficial amygdules are feldspathic and 
in the interior epidotic, or composed of the ferruginous chloritic 
alteration product, delessite. Whatever the interior of the amygdule, 
there is invariably a brownish lining of some decomposition product, 
