One of the Istrian rivers, the subterranean course of which, although still unknown as regards a great number of points, has given rise to a most continuous course of investigations, is the celebrated Timavus (Timavo), which falls into the sea near Duino, about twelve miles to the north of Trieste. Virgil’s description no longer applies to the mouths of the Timavo; at present they do not reach the number of nine, because the extermination of the woods of the Carso has diminished the mass of the water, or the action of the stream and the alluvium of the delta have modified the form of the shore. But still it is a magnificent spectacle to see the outlet of the three principal torrents of water which rush foaming out of the heart of the rocks, and are navigable from their mouths to their very source. A river of this importance must certainly receive the drainage of a vast basin, and yet all the neighboring valleys seem perfectly devoid of rivulets, and their surface presents little else but the bare rock; in fact, the whole of the rain and snow-water runs away through underground caverns. The most remarkable network of caverns in this region of the Alps is that which spreads out from the southwest to the northeast across the Adelsberg group of mountains, between Fiume and Laibach. The principal cave is especially curious on account of its size, the variety of its calcareous concretions, and the torrent which runs roaring through it. North of the town of Adelsberg the traveler passes along the base of a hill with steep and bare sides, bringing into view the sharp edges of its highly pitched calcareous beds. On the right the stream of the Poik winds peaceably in the valley; and then, its course being arrested by a headland, turning suddenly, it flows into the interior of the mountain through a kind of high portal, opening between two parallel beds of rocks. Unless the water in the stream is very low, it is impossible to follow it over the accumulation of rocks upon its bed; but on the right, at a height of a few yards, there is another entry, through which the traveler may descend dry-shod into a vast cavity or chamber, where the Poik again appears issuing from its narrow passage of rocks.