Camping and woodcraft - Scoutmastercg.com

346 CAMPING AND WOODCRAFTThe debris then being disintegrated and washedaway, there remain no traces of the old cavernsexcept ravines or valleys that originally were archedover and were wholly underground. The partthat minute agencies and gentle but persistent forcesplay in building up and reshaping the earth isillustiatedby the fact that most of the limestone itselfis derived from the remains of very small animalsthat covered the floors of the ancient seas.Stalactites and Stalagmites.—Caves are ob^literated by other means than by collapse.Strangelyenough, the very process that hollows out a cavernhas a tendency to fill it up again. Everyonewho has visited a limestone cave of any consequencehas noticed the stalactites hanging from the ceilingand stalagmites rising from the floor directly beneaththem. These are formed in the followingmanner:The vault of a cave chamber is seldom dry.Water still seeps very slowly through it. Now,when acidulated water pours through a crevice inlittle rills it has a cutting and eating effect uponthe rock. But where there is no perceptible crack,and it seeps through the room and falls drop bydrop, each drop remains long enough upon the ceilingto deposit some of its dissolved lime upon theceiling in the form of a ring. The next drop leavesanother layer, and so on. Thus there is built, atfirst, a slender, delicate tube of soft lime resemblinga pipestem. By and by this tube fills up, and ithardens through cr}^stallization. Thereafter itgrows thicker and longer from constant deposits byevaporation on the outside, and it forms what wecall a stalactite.Meantime all those drops that did not evaporatewholly on the ceiling leave the rest of their lime atthe points where they strike the floor. Thus theregrow upward a series of mamillary concretions orstalagmites rising higher and higher toward thelong pendants overhead. In time a stalactite and