CHAPTER IV. 
PETROGRAPHY OF THE IGNEOUS ROCKS. 
The igneous rocks of northeastern Maine show considerable varia 
tion in composition and are represented by members of most of th« 
important rock families. Abyssal rocks are not prominently exposed 
and the number of dikes is relatively limited. The great bulk of th» 
igneous occurrences are of well-marked extrusive lavas in a good statl 
of preservation. The types found in this region are for the most par 
well recognized, and the classification used will require no explanation 
Where this is not the case, the discussion of terms and variations wil 
be found in connection with the various rocks described. 
The subject-matter will be treated in the following order: 
Granites. — Mapleton granite; Drews Lake granite; dark aggregate 
in the Mapleton granite; dikes of the granite areas; metamorphisr 
caused by the granites and associated dikes. 
Rhyolites. — Rock of the main mountain mass; white t}^pe; pcrliti 
type; rhyolite- breccia; vesicular lava. 
Trachytes. — Hedgehog trachyte; trachyte of Chapman Township 
doubtful trachytes; Quoggy Joe quartz-trachyte; quartz-trachyte c J 
township 9, range 3. 
Andesites. — Augite-andesite; hornblende -andesite; andesites c 
southern Mapleton; andesites of Castle Hill; andesite ash beds. 
Diabase. — Aroostook Falls diabase; Mars Hill diabase. 
Teschenites. 
GRANITES. 
The two granite areas in this region are about 40 miles apart, an 
will be considered separately. While it seems best, from the generr 
nature of the rock forming them, to call these masses granite, attei 
tion must be directed to the variable character of the composition ar i 
structure of the rock. 
MAPLETON GKANITE. 
The Mapleton granite is light gray in color, with a pinkish tin|j 
given by the larger feldspars. At first sight the grain seems vei 
coarse, but this appearance is caused by the presence of the larger f el 
spar crystals set in a medium-grained mass of dark and light mineral 
These feldspars might almost be designated phenocrysts. Parts • k l 
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