=Formation of stalagmites.=—Wherever the water percolates through the roof of the cavern so rapidly that it cannot entirely evaporate upon the roof, a portion falls to the floor, and, spattering as it strikes, builds up a relatively thick cone of sinter known as a stalagmite, and this is accurately centered beneath a stalactite upon the roof. In proportion as the cavern is high, the dropping water is widely dispersed as it strikes the floor, with the formation of a correspondingly thick and blunt stalagmite. As this rises by growth toward the roof, it often develops upon its summit a distinct crater-like depression (Fig. 194, lower figure). When the process is long continued, stalactites and stalagmites may grow together to form columns which may be ranged with their neighbors like the pipes of an organ, and like them they give out clear tones when struck lightly with a mallet. At other times the columns are joined to their neighbors to form hangings and draperies of the most fantastic and beautiful design (Fig. 195). [Illustration: FIG. 195.—Sinter formations in the Luray caverns, Virginia.] In remote antiquity limestone caverns afforded a refuge to many species of predatory birds and animals as well as to our earliest ancestors. The bones of all these denizens of the caves lie entombed within the clays and the sinter formations upon the cavern floors, and they tell the story of a fierce and long-continued warfare for the possession of these natural strongholds. The evidence is clear that these cave men with their primitive weapons were able at times to drive away the cave bears, lions, and hyenas, and to set up in the cavern their simple hearths, only in their turn to be conquered by the ferocity of their enemies. Some of the European caves have yielded many wagonloads of the skeletons of these fierce predatory animals, together with the simple weapons of the primitive man. =The Karst and its features.=—Most so-called limestones have a large admixture of argillaceous materials (clays) and of siliceous or sandy particles. Such impurities make up the bulk of the clays and muds which are left behind when the soluble portions of the limestone have been dissolved. [Illustration: FIG. 196.—Map of the dolines of the Karst region near Divača.]