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140 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 
are, however, in this case quartz, and not feldspar. The proportion of 
green mica in the inclusion is much greater than in the granite proper, 
and the colorless microlites are here again abundant. It presents no 
other new features. 
EAST BLUE H1Lu.—This is a coarse rock in which large snow-white 
crystals of orthoclase of an inch or more in length, twinned after the 
Carlsbad law, are frequently developed, giving the rock a beautiful por- 
phyritic structure. Muscovite, magnetite, and zircons are the more com- 
mon accessories. The biotite usually occurs in reddish-brown lamin, 
which are frequently surrounded by a black border of magnetite grains. 
Often, however, it is found altered into a chloritic product, enclosing 
very many small perfect crystals of the magnetite. Black nodules in 
this rock are, so far as my experience goes, very irregular in outline, 
small in size, and quite black. Under the microscope they are found 
to contain the same deep reddish-brown and green mica, enclosing grains 
of magnetite, as does the surrounding granite. There is a very evident 
increase in the proportional amount of feldspar, and a corresponding 
diminution in the amount of quartz. 
Mount WALpDOo.—This is a coarse, gray rock, much resembling the 
last mentioned. The feldspar is in part microcline, and the usual amount 
of apatite and magnetite is present. The nodules in this granite are 
said to be quite abundant, though I have been able to obtain but few, 
one only of which needs especial mention. This is oval in shape, about 
14 by 3 inches in size, of firm texture, and dark gray in color. Almost 
exactly in the center of the fine homogeneous mass of the nodule is a 
large crystal of microcline, some half an inch in diameter. Its angles 
are quite sharp. The finer surrounding material is composed of quartz, 
orthoclase, microcline, biotite, apatite, and magnetite in about the usual 
proportions of the granite, though in a more finely divided state. Color- 
less microlites also occur in these inclusions. 
HURRICANE ISLAND.—In the Hurricane Island rock the feldspar is 
nearly all orthoclase, though under the microscope a few erysfals of a 
plagioclastic variety are seen. Some hornblende is present, though not 
enough to be macroscopically evident. The nodules in this rock are 
quite abundant, and I have examined a considerable number. These 
are usually quite black and of a fine, homogeneous texture. Their out- 
lines are well defined, showing under the microscope an abrupt transi- 
tion from the ordinary coarse texture of the granite to the finer-grained 
inclusion. There is, however, no tendency to separation along this line 
of contact; a thin section of the rock made to include portions of both 
granite and inclusion, after being ground to a thinness of one four hun- 
dredth of an inch, being transferred to the mounting slide without diffi- 
culty. Under the microscope the fine-grained portion is found to con- 
sist of hornblende and biotite in about equal proportion, and in great 
abundance, together with varying amounts of quartz and feldspar. The 
proportion of quartz varies in different inclusions. Sometimes itis quite 
