158 CONTRIBUTIONS TO THE GEOLOGY OF MAINE. [bull. 165. 
with chlorite in bundles and radial growths. Combinations of chlorite 
and delessite form beautiful rosettes and colored vermiculate bodies. 
Limonite is also present in formless masses. The alteration products 
so well exhibited in the cavities are distributed as dots and little masses 
more or less abundantly throughout the section. 
The groundmass is glassy. In places it is entirely amorphous; else- 
where minute feldspar laths lie in an undifferentiated background, and 
in still other places the feldspars lie in small areas of quartz with a 
structure which approaches the micropoikilitic. The glassy ground- 
mass is crowded with crystallites which assume ordinarily rodlike or 
needlelike forms, but which also occur branched or crossed, and in rare 
instances form a radial structure resembling the spokes of a wheel. 
Around each of these crystallike bodies is a colorless zone, indicating 
that the rodlike growth has been built up at the expense of the sur- 
rounding part. The substance which composes the rod and the dark 
parts outside the colorless zone is of the same composition. In the sec- 
tion examined this material is found to be largely chlorite, but from 
the shape of the rods and the character of the alteration it is judged to 
have been mostly biotite. The clear zone surrounding the crystallites 
appears in ordinary light as a light-yellow glass from which the dark 
components have been absorbed to make the center rod. Between nicols 
the glass is found to be partly devitrified, revealing numerous little 
feldspar laths in the glassy base. It is evident that the rock section 
presents the same general appearance under the microscope as when 
fresh and that it is made up of grains and partly formed crystals of 
f erromagnesian minerals in a vitreous groundmass. The minerals have 
altered in composition and the glass is in part devitrified, but the type 
of structure remains unchanged. The appearance of the rodlike bodies 
surrounded by a clear space is seen only in ordinary light. In polar- 
ized light nothing appears except the feldspars in their quartzose and 
glassy base. The accompanying figure (PL XIII, B) will illustrate the 
points discussed above. 
RHYOLITE BRECCIA. 
Macroscopic description. — Near the southeast base of Haystack, on 
the north side of a slight rise of ground, a few small masses of por- 
phyritic breccia are found. The hand specimen shows a greenish-black 
rock with small, waxy-looking feldspar phenocrysts, which differ little 
in color from the main groundmass, but are noticeable for their lustrous 
reflection on cleavage surfaces. Distributed thickly through the por- 
phyry are irregular angular fragments of a pitchstone, which at times 
are as large as 3 to 4 inches in diameter. For the most part these 
glassy chunks have an oily -looking surface of various shades of dark 
green. They are much cut up by a series of fractures, so that under 
the hammer they are broken into little irregular chips. At times the 
pitchstone assumes various shades of red. 
