Postelstia 
(SN) 
(SS) 
Sat 
cient to crowd the flowing rock into every crack 
and cranny of the superjacent formations. When 
crystallized this rock became so hardened that it 
has resisted erosion more than the enclosing 
country rock and it now stands like an ancient 
ruined wall upon the dark shales and slates. In 
age relations the dikes are younger than intruded 
shales and older than all overlying rocks. ‘To 
him who has seen the base of Mt. Edinburgh 
the origin of the dikes seems closely associated 
with the out-thrust of that huge pile of granite. 
During the compressing and tilting of the 
shales as well as subsequent to the intrusion of 
the dikes there were formed master joints and 
minor joints, together with numberless cracks 
anastomosing in every direction. These open- 
ings afforded surfaces on which the decom- 
position processes, yielding large quantities of 
quartz and less quantities of other mineral sub- 
stances, deposited their minerals. This material, 
thus again deposited, filled these cracks and re- 
cemented the rock into a solid mass. Thus the 
veins were formed which present so striking a 
feature of many a rock surface. They are al- 
