224 Collie—Geology of Conanicut Island , R. /. 
is parallel to the gliding plane, when rotary motion would 
cease. 
The rocks of Beaver Tail show a more constant and higher 
degree of schistosity than the rocks of Conanicut proper. Meta¬ 
morphism in all its phases is more noticeable in passing from east 
to west, the folds are more frequent, more compressed, more 
overturned, fracturing and granulation of included fragments is 
more common, schistosity is more abundantly displayed, sericite 
more plentifully developed, as is always the case in this area, 
sericite is an index of the amount of dynamic metamorphism. 
All these phenomena are an increasing factor to the westward, 
combined with this feature is another, namely that the sedi 
ments of the rocks become coarser to the westward, in tha 
direction we approach an old shore line, and it is probably true 
that from this old land the forces which caused metamorphism 
came, since the evidences of metamorphism have greatly in¬ 
creased as this area is approached. 
The contacts between the light and dark schists afford op¬ 
portunity for noting the contrasts between the two rocks. The 
white schist is more compact and homogeneous; the black is 
divided by innumerable distinct cleavage plans. Though cleav¬ 
age is present in the white, it does not manifest itself as in the 
black. This is due to a variety of causes. In the first place 
the light schists are composed almost wholly of sericite flakes 
arranged parallel to the schistosity, together with rutile needles 
and occasionally a grain of quartz hidden in the meshes of the 
seiicite. There is no contrast of different colored minerals to 
bring out the structure of the schistosity. On the other hand, 
the dark schist has a darker sericite, which is. filled and colored 
by black specks of iron oxide or graphite, together with numerous 
light-colored rutile needles, which contrasting with the dark 
background make the structure more tangible. Each minute 
cleavage plane is filled with very dark graphite flakes, and the 
course of each plane is easily traceable. The contrast between 
the black graphitic layers and the lighter intervening ones is 
so sharp that the attention is at once drawn to the structure. 
The black schists frequently are not so exclusively composed of 
sericite, but contain much quartz and some feldspar. The 
