Postelsia 337 
dock. The rocks here lhe at an angle of in- 
clination exceeding 50° from the sea level. The 
uplifting of Mt. Edinburgh more than 4,000 feet 
produced by its intrusion such a squeezing to- 
gether that the fine elastic particles, compressed 
by a force exerted against the enormous beds 
of shale, yielded at right angles to this pressure. 
This yielding flattened the particles and pro- 
duced a direction of weakness, a capacity to 
part which is called slaty cleavage. The broad, 
long slabs which le about give evidence of this 
induced condition in the rock. Furthermore, 
it is to be noted, that the mineral composition of 
this slate differs from the schist of Providence 
Cove and the shale at the Station,—from the latter 
in being more uniform in composition and from 
the former in being as clearly an argillaceous- 
carbonaceous rock as that is a siliceous one. 
Apphed the same pressure, temperature and 
time, the one is converted into a schist and the 
other into slate. 
Aside from sedimentation and molecular 
change other forces have operated. Dikes and 
veins have taken their place in the varied mass 
