222 
Collie—Geology of Gonanicut Island, R. I. 
pressure, if the movement which formed these had continued, 
the folds would have become closely appressed, fractures would 
have appeared along the crest of the ridges and thus gliding 
planes or incipient schistosity would have arisen. Examples in 
which this further action has gone on are found in the Conanicut 
rocks. In a general way the black schist series of Conanicut 
Island consists of fine carbonaceous schists alternating with fine 
grits or conglomerates. The alternations are frequent and 
forcibly illustrate the unstable condition of the land during the 
deposition of the thin beds. 
Through a series 1,200 feet thick the same conditions do not 
exist for more than a few feet consecutively. 
This series above described includes the principal formations 
of Conanicut. On the smaller island locally known as Beaver Tail, 
the same series occurs in much the same order. So close is the 
resemblance that the rocks do not need especial description ex¬ 
cept in those few instances where there is an abnormal develop¬ 
ment of cleavage or folding. The light colored sericite and rutile¬ 
bearing schists predominate with frequent inter-beds of graphite 
schist. The banded black and white schists are a prominent 
feature at Hull’s Cove. The schists stand vertically, the cleav¬ 
age being developed at right angles to this, thus presenting 
that unusual phenomenon, in which the bedding is vertical and 
the cleavage at a very low angle. 
The most interesting phenomenon of these banded schists, as it 
is indeed of the whole island, is the behavior of the garnet grains 
while under pressure. When the force began to act which pro¬ 
duced the perfect schistosity found in these rocks, the inclusions 
were forced either to adjust themselves to this pressure or fail¬ 
ing in that to be crushed to fragments. In many instances the 
former plan was adopted and the phenomenon is presented of 
garnet grains and quartz fragments turning in their beds until 
their longest diameter was parallel to the schistosity. Both 
methods above mentioned are repeatedly found in the schist. If 
the grains were brittle, they were crushed to a mosaic, and then 
flattened out into long lenticular augen. If they were unable 
to resist pressure they turned in situ. The attempt on the 
part of individual grains to turn rarely met with complete sue- 
