As far as these subterranean streams have been explored, their course exhibits a wonderful variety of interesting underground scenery. Sometimes they form high cataracts, leaping over rocks so picturesquely grouped that, were they illumined by the sun, and of more easy access, they would be admired by numberless tourists; and not seldom they expand into dark and melancholy lakes. Sometimes they with difficulty force a passage through a chaos of rocks, and then again they flow gently in a deep and even channel, so as to be navigable to a considerable distance. Generally, not the least breath of air sweeps over their placid waters, but sometimes their surface is rippled by the wind pouring in through some unseen chasm. Among the bold explorers who have launched forth their barques on unknown subterranean rivers, the late Adolph Schmidl, of Vienna, holds a conspicuous rank. In a canoe specially constructed for the purpose he trusted himself to the dark streams of Carniola, which rewarded his adventurous zeal with many a scene of incomparable beauty, where the water-spirits and the gnomes seemed to have rivalled each other in the work of decoration. To give an idea of the difficulties and of the enjoyments of these subterranean explorations, we will follow the intrepid naturalist on his voyages of discovery through the famous Cave of Planina, through which flows the Poik, a river which is at all times deep enough to carry a boat. The course of the navigation is stream- upwards, and consequently much safer than would otherwise have been the case; but in many places the rapidity of the current calls for great caution, and considerable strength is needed to overcome its violence; while at the same time great care must be taken to avoid striking against the rocks that lie hidden under the water. As far as the end of a magnificent dome, situated about 600 feet from its entrance, the cave can be traversed on foot; but here the sullen stream, completely filling its whole width, compels the explorer to trust to his canoe. When he has passed a portal about eight fathoms high and half as broad, with proportions as symmetrical as if it had been sculptured by the hand of man, the thundering roar of a distant cataract announces still grander scenes. The portal widens, and the astonished explorer suddenly emerges on a lake 250 feet long and 150 feet broad, beyond which the cave is seen to divide into two arms, giving passage to two streams, whose confluent waters form the lake. This broad sheet of water affords an imposing but melancholy sight. The walls of the cave rise everywhere abruptly out of the water, with the exception of one small landing-place opposite to the portal at the foot of a projecting rock or promontory. Here and there large masses of stalactite hang like petrified cascades from the rocks, which are generally naked and black. The vault is so high that the light of a few torches fails to pierce its gloom, which is