The Ottrelite Schist. 
219 
change of level, there was a deposition of coarser detritus. This 
alternation of conditions was rapid, as is indicated by the thin 
beds. The instability of the land lasted during the deposition 
of this great series of schists, for the repeated alternation of 
beds continues to the top of the series. One of the uppermost 
members is a coarse thick-bedded conglomerate, formed largely 
of quartz pebbles ranging in size from one inch to four or five 
inches in diameter. The strike and dip of the beds agree with 
that of other members of this series in northern Conanicut. 
It is this hard resistant rock which gives rise to the long ridge 
in the center of the island. 
Throughout the carboniferous schists there are a great num¬ 
ber of quartz veins. At the points of intersection masses of 
quartz are formed five or six feet in diameter. The shore is 
strewn with these quartz blocks, which are a prolific source of 
pebbles. Often in the vicinity of such veins the beach is made 
up wholly of fragments thus derived from the veins. There is 
now going on a repetition of the processes by which the great 
beds of quartz conglomerate were formed in the past. 
As already stated the rocks of western Conanicut are more 
disturbed than those of the east side. This is shown by the 
greater degree of folding, by the greater dip of the rocks, and 
microscopically by the relatively greater amount of crushing 
which the constituent minerals have undergone. As a whole 
the texture of the west shore rocks is also coarser. There is 
more grit and conglomerate in this locality. Evidently the an¬ 
cient shore line is being approached in passing from east to 
west. 
THE OTTRELITE SCHIST. 
The schists at the northern extremity of the island contain 
ottrelite in many localities. The ottrelite bearing rock is 
quartzose, indeed closely resembles quartzite, and it lies inter- 
bedded with the graphite schists in thin layers, which do not 
extend to any great distance. The occurrence resembles cores 
of coarse rock included in the black schists. They may be re¬ 
garded as lenticular augen included in the schist. The masses 
of rock contain numerous rhomboidal crystals of ottrelite irreg- 
