PROTRUSION OF SOLID GRANITE. 
575 
Mr. T. McKenney Hughes has suggested to me in explana¬ 
tion of these phenomena that they may be the effect of the 
association of more pliant strata with hard unyielding rocks, 
the whole of which were subjected simultaneously to great 
movements, whether of elevation or subsidence, and of lateral 
pressure, during which the more solid granite, being incapa¬ 
ble of compression, was forced through the softer beds of 
shale, sandstone, and limestone. He remarks that similar 
breccias with slickensides are observed on a minor scale 
where rocks of different composition and rigidity are con¬ 
torted together. Such protrusion may have been brought 
about by degrees by innumerable shocks of earthquakes re¬ 
peated after long intervals of time along the same tract of 
country. The opening of new fissures in the hardest rocks 
is a frequent accompaniment of such convulsions, and during 
the consequent vibrations, breccias must often be caused. 
But these catastrophes, as we well know, do not imply that 
the land or sea of the disturbed region are rendered unin¬ 
habitable by living beings, and by no means indicate a state 
of things different from that witnessed in the ordinary course 
of nature. 
