162 CONTRIBUTIONS TO THE GEOLOGY OF MAINE. [bull. 165. 
occur as rectangles three or four times as long as broad, which present 
clear-cut outlines and do not show the ragged, stringy, thunderbolt 
forms found in the Chapman trachyte and the andesite from Edmunds 
Hill. No dark-colored mineral appears in the rock, and the chlorite 
present in considerable amount gives no clue as to the mineral it has 
replaced. The groundmass is arranged with remarkably good flow 
structure. Practically all the feldspar microlites are arranged with 
their longer axes parallel, and the streams which they form are seen 
to divide in order to pass around the quartz-filled vesicles and then to 
reunite beyond. The section examined contains a fragment of a some- 
what different igneous rock, which, judging from the manner in which 
the lava has flowed about it, appears to have been dropped into the 
lava flow while in motion. 
TRACHYTE OF CHAPMAN TOWNSHIP. 
Macroscopic description. — When seen in the ledge the appearance of 
this rock is very deceptive. It has there a brownish-black color, 
smooth feel, and presents little tables with angular outlines rather 
than round-cornered fragments. However, when the rock is broken, 
so as to expose fresh material, the brown color and smooth feel are 
seen to be confined to a very thin layer on the outside, while the main 
mass has a very light-gray color with a bluish cast and a rough feel, 
and breaks into sharp, irregular chips. In general the rock is dense 
and uniform and specked with minute black dots, which at times are 
large enough to be distinguished as cavities with black lining. Feld- 
spar crystals, stout, or more often long and very narrow, are scattered 
inconspicuously through the mass, and would be scarcely noticeable 
except for their glistening cleavage faces. The whole rock is marked 
by numerous slits or flat, slender cavities, short and small, but some- 
times half an inch in length. Their longer axes are parallel to one 
another and approximately horizontal. These slits represent the cavi- 
ties of a highly vesicular lava which have been drawn out from their 
spherical shape by movements of flow. 
The cavities are now usually empty, being only lined with a rusty- 
yellow substance, but some of the larger ones are filled with calcite or 
quartz. So distinctly trachytic is the rock in its general appearance 
and decided flow character that from an examination of the hand speci- 
men alone one feels safe in designating it a feldspathic lava. 
Microscopic description. — Under the microscope a few feldspar 
phenocrysts and patches of chlorite are seen to lie in a groundmass 
of feldspar laths. Quartz is also present. The larger feldspars are so 
cut in the section as to show squares, or, more often, narrow laths half 
a millimeter long. Carlsbad twinning occurs with irregular division 
line between the two halves, and from this line tongues of one twin 
