Oil A PT E R II. 
IGNEOUS ROCKS. 
Northeastern Maine is essentially a region of sedimentary rocks, 
among which igneous outcrops occur to a relatively small extent. 
The most numerous exposures of igneous rocks are located in Castle 
Hill and Mapleton townships, where they form the prominent topo- 
graphic features (see map, PL IV). Even here, however, their 
extent is quite limited. It is an interesting fact that, although the 
distribution is so limited, the number of well-defined igneous types 
is large and shows wide variation in character. 
It is the purpose of this chapter to discuss the general structure, 
nature, and field relations of the igneous rocks of this region, and to 
leave the microscopic and chemical descriptions to the succeeding 
chapter. A third chapter will briefly treat of the general petro- 
graphic questions presented by a study of this area. 
The igneous rocks occurring in northeastern Maine will be described 
under the following heads: Granites, Rhyolites, Trachytes, Andesites, 
Diabase, Teschenites. 
GRANITES. 
Granite occurs in two small areas within the region described in this 
report. One is in the northeast corner of Mapleton Township, near 
the Aroostook River; the other is near Drews Lake. Neither exposure 
is topographically conspicuous, and it is not surprising that one of 
them has heretofore escaped notice. From the general character of 
the region a wider distribution of granite rocks was to be expected. 
MAPLETON GRANITE. 
The Mapleton granite (locally known as Munson's granite) forms 
part of a low, rounded hill, which has suffered so much erosion that no 
sharply defined ledges remain. The top of the hill is a tablelike mass 
covering some 6 or 7 acres, and bounded on the east, where it nears 
the calcareous slates, by a low cliff. The north side gives the best out- 
crops, and the slope is covered with slabs of granite which have been 
loosened above by the frost. The rocks on tin- west and south sides 
of the hill are completely obscured by products of forest decay. The 
granite, as shown by its outcrops, forms an oblong mass, with northeast - 
southwest axis, about 1 mile long and one-fourth mile wide. It has 
probably a somewhat greater extent, however, as shown by the fact 
that where the sedimentaries first appear to the west — about one-eighth 
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