The Schists. 
209 
not a local exposure. It is everywhere present, lying between 
the granite and the overlying schist. Well diggers state that 
in all parts of the island they invariably come upon a layer of 
“rotten granite” before the hard granite is reached. 
It has been affirmed by some investigators that the arkose is 
fault breccia or possibly debris resulting from shearing move¬ 
ments in the granite itself. This view is not a tenable one, 
for the arkose is found only at the granite-schist contact, it 
follows all of the irregularities of this contact, it lies in the 
hollows and on top of the ridges of the granitic surface. It is 
inconceivable that faulting or shearing could occur upon so 
uneven a surface as that afforded by the granite and at the 
same time the fault plane or the shear plane invariably lie 
between the contact of the schist and granite. Faulting and 
shearing is a common feature in the granite area, but nowhere 
is it accompanied by large quantities of breccia, nor is the 
breccia of the nature of arkose. The former consists of 
broken fragments of granite, the latter of quartz imbedded in 
detrital feldspar. 
The arkose is absent from the granite-slate contact. This 
circumstance when considered in connection with other contact 
features proves the priority of the slate. The presence of this 
decayed mantle at the granite-schist contact also proves the 
latter to be the later formation. The relationship of the gran¬ 
ite with the two clastic formations immediately joining is 
clearly proven even if other proofs were wanting by the arkose 
alone. The granite is younger than the slate, it is older than 
the schist. The relationship here indicated ought also to dis¬ 
prove the repeated assertion that the hard compact slate is a 
metamorphosed state of the schist, the metamorphism having 
been produced by the granite intrusion. The occurrence of the 
arkose alone disproves such a view. 
THE SCHISTS. 
Immediately overlying the arkose on the west shore and the 
slate on the east shore is a series of schists which constitute 
the principal formation of the island. These schists are carbon- 
14 
