262 THE BORDERLAND OF SCIENCE. 



rocking forces, there is a region in which rocks of 

 grotesque figure attest the perfect immunity which the 

 region has enjoyed even from inconsiderable shocks. 

 The Cheese-ring in Devonshire is another instance of 

 the kind of evidence we are considering. 



And as there are instances of regions near to a 

 disturbed district which yet are free from shocks, so 

 there are spots liable to frequent shocks though the 

 neighbouring country for miles on every side is seldom 

 (if ever) disturbed. Such is the district very limited 

 in extent near'Comrie, in Perth, where a year scarcely 

 ever passes without a shock being experienced. 



It would seem also as if regions free from subter- 

 ranean disturbance for many centuries must not count 

 upon permanent immunity. For a violent earthquake 

 will often open out, as it were, a passage for subterranean 

 impulses to new regions. 'The circles of concussion 

 enlarge,' says Humboldt, ' in consequence of a single 

 extremely violent shock.' Since Cumana was destroyed 

 (December 14, 1797) every shock of the southern coast 

 is felt in the peninsula of Maniguarez, which before 

 suffered no disturbance. Again, in the successive 

 earthquakes which traversed (in 1811-13) the valley 

 of the Mississippi, Arkansas and Ohio rivers, it was 

 noteworthy how the motion travelled farther and farther 

 northward on each occasion. It seemed as if the subter- 

 ranean forces were gradually breaking a way through 

 successive barriers. 



We have seen so much of the earthquake as an agent 

 of destruction, that it may sound paradoxical to assert 



