356 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
another locality west of Owen’s walk in the Fells, an inclusion of 
aplitic granite, containing quartz, orthoclase, plagioclase, and a 
small amount of microcline, occurs in a dike of the oldest series, 
described below as probably lamprophyric phases of the granite 
magma. The source of this inclusion has not been located. 
Thi’ough the granite at the north end of the area was intruded 
a series of dike-like masses of basic rock whose general trend is north 
and south. What may have been the original constitution of these 
masses is now obscure; at present they must be classed with the 
schistose rocks. The most southern of these (see map) are horn¬ 
blende schists, consisting of much quartz and hornblende with a 
more or less distinct banded structure, the hornblende prisms being 
arranged in rows parallel to the bounding walls of the dike. Small 
amounts of biotite, plagioclase, and magnetite are present, together 
with secondary chlorite and epidote. The largest member of the 
series, represented on the map at the north end, and west of Forest 
street, shows, even in small hand specimens, alternate plicated bands 
of white quartz and dark biotite, the latter in larger amounts. The 
thin section shows that the rock consists almost wholly of quartz in 
small angular anhedra, and small plates of biotite. Both the horn¬ 
blende and the biotite schists carry fragments of the granite. 
These latter, beyond the usual secondary minerals and the warped 
twinning lamellae of the plagioclase, show no essential changes. It 
is inferred that these schistose bands are altered lamprophyric 
phases of the granite, intruded from beneath after the partial solidi¬ 
fication of the more acid rock. The irregular boundary walls, and 
the fact that the joint planes cut both granite and schists, would 
appear to indicate that the jointing of the granite was subsequent to 
the intrusion of these basic masses. 
Felsites. — The middle portion of the area is occupied by a series 
of rocks which, taken collectively, may be called felsite (acid por¬ 
phyries). They are, for the most part, pink in color, and show a 
cryptocrystalline structure on a freshly fractured surface. Micro¬ 
scopical! jq the rocks of the larger portion of this part of the area 
show the intergrowth of quartz and feldspar characteristic of micro- 
granitic structure. In some cases, the rock appears to consist almost 
wholly ©f this quartz-feldspar ground mass, but occasionally irregular 
grains of quartz appear and phenocrysts of feldspar, both orthociase 
and albite (quartz granophyr). On the one hand, this granopbyr 
