MOUNTAIN FORMATION 



Trieste have been explored to a distance of several miles. 

 The River Poik has broken into one part of the labyrinth 

 of chambers through which it rushes before emerging 

 again to the light. " Narrow tunnels," says Sir Archibald 

 Geikie, " expand into spacious halls, beyond which egress 

 is again afforded by low passages into other lofty recesses. 

 The most stupendous chamber measures 669 feet in 

 length, 630 feet in breadth, and 111 feet in height. From 

 the roof hang white stalactites which uniting with the 

 floor form pillars showing endless varieties of form and 

 size." Still more gigantic is the system of subterranean 

 passages in the Mammoth Cave of Kentucky, the accessible 

 parts of which are believed to have a combined length of 

 about 150 miles. The caverns of Luray, in Virginia, are 

 scarcely less wonderful ; and in their case American in- 

 genuity has hit on the idea of sucking the pure, dustless 

 air out of these caverns in order to ventilate a sanatorium. 

 Indeed, a book might easily be written on the wonders of 

 the limestone caverns of the world, but our only purpose 

 in mentioning them in this chapter is to indicate how the 

 rocks of the earth may be made unstable, so that a slight 

 shock may precipitate a catastrophe in them a kind 

 of subterranean landslip which in its turn may give rise to 

 some of the symptoms of earth tremors. 



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