IPo s t e I sia 331 



dock. The rocks here lie at an angle of in- 

 clination exceeding 50° from the sea level. The 

 uplifting of INIt. 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 lie 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. 

 Applied 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 



