62 THE WORLD'S LUMBER ROOM. 



excavated by the mechanical action of the Poik, which at 

 one part of its course disappears through an opening in the 

 earth, and flowing underground for several miles, passes 

 through one of the great halls just described on its way. 



In South Australia there is a series of limestone caverns, 

 one of which has the appearance of an immense Gothic 

 cathedral, the roof being apparently supported by one huge 

 stalactite, tinted with almost every shade of colour, while 

 the area is occupied by numerous half-finished stalagmites, 

 which look, in the dim light, like kneeling worshippers. 

 The stalactites in each cavern seem to possess a distinct 

 character of their own, and differ one from the other as much 

 as do the leaves of the forest. 



In one of the Bermuda caves there are grand stalag- 

 mitic columns reaching from floor to roof, one of which is 

 beautifully fluted and fretted with stalactites, and measures 

 sixty feet in circumference ; in another the stalactites hang- 

 ing from the roof are perfectly white, some of them as fine 

 as knitting-needles, and often yards long ; while, wherever 

 there is a continuous crack in the roof, there descends from 

 it a graceful, soft-looking, white curtain. 



Of all the limestone caves hitherto discovered, however, 

 the most extensive is the Mammoth Cave, of Kentucky, 

 which, with its 226 avenues branching out from the main 

 gallery, is computed to have a total length of about 160 miles. 



But our chief point now is, that, whether excavated by 

 chemical or mechanical means, or by both, the vast quanti- 

 ties of limestone which once filled such caverns have been 

 carried away to the ocean by the springs, streams, and 

 rivers, which permeate and overspread the earth. 



