128 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Type 2. Biotitic Granite (Granitite) .— The second type 
of granite is found wholly south of the Blue Hill Complex, as deter¬ 
mined by Professor Crosby, in the south parts of Weymouth and 
Braintree, in Randolph, etc. 
It is a light-colored granite of medium coarse texture, and, as the 
hand specimen shows, is rich in quartz, white, light gray or sometimes 
greenish feldspar, and scattered fragments of biotite of considerable 
size. Rarely a little hornblende is seen. The three constituents 
seem to be remarkably evenly distributed in quantity throughout the 
mass of the rock. - Occasionally segregations of a few centimeters in 
diameter occur, in which the minute grains of biotite are especially 
abundant, imparting a darker color to these patches. This type of 
granite is quite representative of what German petrographers denote 
as Granitite. Under the microscope the feldspar proves to be 
both monoclinic and triclinic. The former frequently exhibits mi- 
croperthic intergrowths and granopheric rims, and is occasionally 
twinned according to the Carlsbad law. The plagioclase shows 
handsome zonal twinning according to both the albite and pericline 
laws. The biotite is in brown scales and is idiomorphic in nearly 
all cases, sometimes appears to have been strained and frayed on 
the edges. In the quartz this straining is often quite marked, and 
the grains seem to have been twisted even though they lie closely 
packed in the interstices of the plagioclase. Between the larger 
mineral fragments a fine microgranitic structure is apparent. The 
rock seems to be free of accessory minerals, with the exception of a 
few magnetite grains. 
Tv r PE 3. Hornblende Granite. — The typical Quincy granite 
of the quarries, often referred to as “ syenite ” by Hitchcock (’41, p. 
668) and Hunt (’75, p. 188), 1 occurs throughout the quarries of West 
Quincy and thence southwesterly along the northern border of the 
Blue Hills area, where it merges into the succeeding types of por- 
phyritic development. 2 
Macroscopically it is a coarse holocrystalline aggregate of white or 
bluish orthoclase and smoky quartz; these forming the bulk of the 
rock; with dark green or black hornblende having marked prismatic 
cleavage, which in places is altered to a lighter green chlorite. The 
1 See also Godon ( 09, p. 137), Dana, J. F., and Dana, S. L. (T8, p. 205), Smock ('90, p. 231 
Shaw (’GO, p. 353), and Bayley (’88, p. 207, 295). 
2 Dodge (’83, p. G5-71) claims that there are two granites in the Quincy district, but 
gives no evidence . 
