Further down the stream the Poik is not visible again until it emerges from the mountain, where it is known under the name of the Planina; it rushes out through a circular arch at the base of a perpendicular bluff crowned with fir-trees. It really is the Poik, as is proved by the equal temperature of water and the sudden increase of its liquid mass after a storm has burst at Adelsberg; but the stream always issues from the cave much more considerable in bulk than it is when it enters, owing to the tributaries which pour into it on both sides during its subterranean course of five to six miles. One of these rivulets, which comes down from the plateaus of Kaltenfeld, joins the Poik at a little distance from its outlet. Above the confluence the principal stream can be ascended in a boat to a distance of more than 3,500 yards, which, with the other explored parts of the subterranean river, makes about three miles. Below the point of outlet the stream is partially lost in the fissures of its bed, and then, joining the Unz, goes on and empties itself into the Danubian Save. About a dozen miles to the southeast of the Adelsberg and Planina caves extends a large plain surrounded on all sides by high calcareous cliffs, at the base of which nestle seven villages. In this hollow, the most elevated portion of which is under cultivation, the remainder being covered with rushes and other marsh-plants, there are to be found more than 400 funnel-shaped holes resembling those in other parts of Carniola. These _dolinas_, the average depth of which is from 40 to 60 feet, have each their special name, such as the “_Grand Crible_” (great sieve), the “_Crible-à-froment_” (corn sieve), the “_Tambour_” (drum), the “_Cuve_” (tub), the “_Tonneau_” (cask), pointing out the form or some remarkable peculiarity of each abyss. During extremely dry seasons there is only one of these cavities which contains any water; but after continuous and heavy rain, the water of a stream which is swallowed up in the rocks a little above the plain rises with a roaring noise in each of these wells. Torrents escaping from all these open “_cribles_” form in the wide space hemmed in by the cliffs a sea of blue and transparent water. This is the lake of Jessero or Zirknitz, the _lacus Lugens_ of the Romans. The surface of the sheet of water extends over an area of 14,826 acres; at the time of great inundations, this extraordinary temporary lake, thus vomited out by the underground river, is not less than 24,711 acres. The water runs away through a subterranean channel, and, further on, empties itself into the Unz, below the Planina.