Gregory.] METAMORPHISM. 151 
Quartz is in larger grains than any other mineral except the feldspar, 
but also occurs in small grains in the groundmass. It has rolling 
extinctions and is muddied by inclusions. 
Kersantite. — This rock is found only in connection with the Mapleton 
granite area where it outcrops in the river in two dikes. One of these 
is small, the other is 500 feet or more wide. It appears as a very dark, 
stone-gray, cryptocrystalline rock with glistening surface. So far as 
can be seen without the microscope, the texture is uniform. When 
examined under the microscope a thin section shows the presence of 
iron ore, abundant apatite, biotite, hornblende, plagioclase, orthoclase, 
and quartz. Biotite is ragged and stringy, usually grouped in irregu- 
lar masses, and largely altered to chlorite. The hornblende is also 
mostly changed to chlorite and is not abundant. The plagioclase is 
oligoclase-andesine with the formula Ab 3 An 1? as shown in its extinc- 
tion angles in Carlsbads by the Michel Levy method. Orthoclase is 
in almost square laths; a few show twinning. The feldspars are much 
altered and eaten into, the cavities now filled with calcite. The struc- 
ture is dense granitic, verging toward porphyritic from the develop- 
ment of some plagioclase larger than the average. 
This rock has the characteristic lamprophyric appearance, and this, 
taken in connection with the excess of plagioclase over orthoclase and 
the abundant mica, shows it to be a typical kersantite. 
METAMORPHISM CAUSED BY THE GRANITES AND ASSOCIATED DIKES. 
Mapleton area. — The Aroostook River, where it flows through the 
townships of Washburn, Mapleton, and Presque Isle, gives a good 
section through the region affected by the Mapleton granite area. The 
outcrops along the river east of Washburn Ferry show the general 
country rock to be a black arenaceous limestone, thin-bedded, and alter- 
nating with beds of gritty material which under the microscope proves 
to be composed largely of broken pieces of quartz, feldspars, and calcite. 
Following the river downstream, the first marked change in the char- 
acter of the rock is seen where it occurs between a dike of aplite and 
one of syenite. Metamorphism has here produced a compact schist of 
a grayish -green hue, prettily marked by a multitude of tine bands and 
lines of various shades of gray, representing the bedding planes in the 
old shale. The rock is so cut through by intersecting cleavages that 
only hand specimens can be removed. The acid test shows a very 
little lime, mostly in the white bands. With the aid of the micro- 
scope we find the main mass composed of lime garnet (grossularite), 
some pyroxene, calcite in bunches, and a little quartz and iron in a 
background of feldspar. This corresponds very well with the expected 
metamorphic changes in the gritty layers of the country rock. Side 
by side with this banded schist we find la} T ers of impure marble which 
may represent the more limy parts of the general slates. Farther 
