126 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
idiomorpliie when alone and not broken by strains. When with 
hornblende the borders are irregular, probably due to resorption into 
the magma and recrystallization as hornblende. The biotite contains 
various minerals between its leaves. The most prominent of these 
are rutiles regularly crossed at angles of 60° according to the 
sagenite law of DeSaussure. 1 In some cases these crystals are very 
line and close. Small crystals of apatite occur also in the leaves 
of biotite, showing the perfect hexagonal cross section. 
Hornblende is very pleochroic and has the prismatic cleavage 
strongly developed, with a lighter green chloritic alteration which 
is scarcely pleochroic. 
Magnetite is plentiful and some ilmenite occurs, with limonite 
alteration in the cracks. The magnetite crystals are often sur¬ 
rounded and intergrown with fresh hornblende and some biotite. 
Hear the slate contact the granite is finer grained and dark 
colored. The contact of the slate and granite in the railroad cut 
near Weymouth station exhibits the peripheral phases of crushed 
granite, with decomposed pyrite and chlorite, and dust in the 
highly polarizing quartz. These are probably largely the result 
of faulting that has subsequently taken place along the original 
igneous contact. The granite as it approaches the slate becomes 
felsitic, and is a heavy greenish or reddish rock, in its extreme 
phase being a compact felsite (not like the aporhyolites however) 
without phenocrysts, and under the microscope presenting only a 
dusty and iron-stained appearance. 
The included diorite is of a green color, in pieces from several 
inches up to some feet in diameter, and varies in texture from 
very compact and uniform to coarsely crystalline. Microscopically 
the feldspars appear to be chiefly plagioclase, the remainder being 
decomposed orthoclase. 
Epidote, evidently an alteration of hornblende, occurs in the 
feldspar. 
Mica has changed chiefly to chlorite with limonite discoloration. 
The amphibole is a green hornblende occurring as interlocking 
crystals with a yellowish alteration. The secondary hornblende is 
uralitic, with pale yellow and green pleocliroism and a higher 
extinction than in the brown portion. 
1 See G. H. Williams (’83, p. 617) on similar rutiles interposed in the mica of a 
porphyritic diorite from the Black Forest (near Tryberg), Germany; also Iddings (’89, 
Figs. 56 and 58). 
