MUSEUM OF COMPARATIVE ZOOLOGY. UGt 
find any outcrop of it.” The carboniferous schists abound in little 
black metallic plates which resemble ottrelite, so that the rock may 
have been mistaken for ottrelite schist ; but since pebbles of this rock 
are associated with pebbles of the true ottrelite schist, there is little 
reason to doubt that the latter occurs in place in the vicinity, and prob- 
ably of Carboniferous age.” 
Ottrelite Schist. — The ottrelite schist here described was collected by 
Mr. Dale, occurring as pebbles on Easton’s Beach, Newport. The rock 
is a silvery-gray, fine-grained mica schist, which has a well marked 
schistosity (and cleavage), the plane of which bears no relation to the 
distribution of the ottrelite. This mineral occurs in the well known 
rhomboid or irregular plates, three or four millimeters in diameter, 
with brilliant lustre and well marked cleavage surfaces. The latter are 
pitted with little dull spots, which it is seen in the slide are grains of 
quartz enclosed by the crystal. 
Studied in the thin section, the rock is found to be composed of little 
rounded grains of quartz, closely interlocking, when not separated by 
the other constituents, and of minute scales of colorless mica with the 
optical properties of muscovite, which by their parallel arrangement 
cause the schistosity of the rock. Certain wavy lines oblique to this 
structure, which contain less mica and more quartz than the average, 
may represent the original plane of deposition. A darker variety of the 
rock contains occasional small plates of chlorite and bands of opaque 
black substances, which are mixtures of graphite and titaniferous iron 
ore (ilmenite?) for the powdered rock gives a strong test for titanium 
and also for graphite. 
The ottrelite crystals and somewhat smaller black metallic plates are 
seen to have no connection with either the plane of schistosity or 
possible deposition plane. The former mineral occurs in plates of 
irregular outline, appearing as lathe-shaped cross-sections, frequently 
twinned several times, with composition parallel to the base, blue and 
greenish pleochroism, and the other usual optical properties. They are 
generally filled with little grains of quartz of the same size and shape as 
those composing the rock outside, which were evidently enclosed by the 
crystal as it formed ; it is noticeable that the muscovite never accom- 
1 A contribution to the Geology of Rhode Island, Am. Journ. Sci., Vol. XX VII. 
p. 222. 
2 Mr. Dale has found ottrelite schist in place on Conanicut Island, opposite New- 
port, but the rock has not been examined microscopically. Proceedings of Cana- 
dian Institute, 1884-85, p. 21. 
