Microscopic Features. 
205 
moot extreme, it is light green in color, through the chloritiza„ 
tion of the feldspars, and gneissic in structure. The granite is 
all more or less jointed, slickensided surfaces frequently occur and 
the porphyritic constituents are often crushed to a mosaic or 
drawn out into augen. These evidences of movement and press¬ 
ure are most abundant on the west shore. The joints are filled 
with quartz, the veins thus formed sometimes reach a width of 
two feet. In approaching the island from the sea, they form a 
striking contrast with the dark red granitic cliff for a back 
ground. A large number of pegmatite veins intersect the gran¬ 
ite, with rare exceptions they do not exceed three or four inches 
in width. They closely resemble dikes in appearance. Their 
width is uniform throughout their length, they have sharply de¬ 
fined walls, there is no gradual transition from the granite to 
the pegmatite, but the contact is a sharp and clearly defined 
one. The small veins of pegmatite have not been observed out¬ 
side of the granite, the structure is invariably fine in the small 
veins, but is much coarser in the larger ones. 
MICROSCOPIC FEATURES. 
The granite contains a large proportion of quartz, the biotite 
is irregularly distributed and is comparatively rare, it is usu¬ 
ally altered to chlorite. The feldspar is usually much fissured 
and weathered, especially in the western area, and here the fine 
fissures are filled with chlorite, more rarely with epidote and 
calcite. It is stained a dull reddish brown color by the iron 
oxide which is abundant in these rocks. The extent to which 
metamorphism has gone on can be fairly well judged by the 
microscopic appearance. The deeper the green color of the 
rock, the greater the metamorphism, and vice versa. The feld¬ 
spar occurs in rather coarse holocrystalline grains, and also as 
large phenocrysts in the granitic ground mass. Orthoclase and 
plagioclase occur both as ground mass and porphyritic crystals, 
but the orthoclase predominates. The quartz is a very large 
constituent of the granite and occurs in coarse grains, which are 
filled with numerous liquid inclusions, often to such an extent 
that they give the mineral a dark blue color. The mineral is 
not clear and pellucid, but is dark and quite opaque. This is 
