The aspect of the crystalline mountain masses to the west of the Vardar is altogether of an Alpine character, for the peaks not only attain a high elevation, but snow remains upon them during the greater portion of the year. The Gornichova, or Nije, to the north of Thessaly, rises to a height of 6,560 feet; and the Peristeri, whose triple summit and snow-clad shoulders have been likened to the spread-out wings of a bird, and which rises close to the city of Bitolia, or Monastir, is more elevated still. The mountains of ancient Dardania enclose extensive circular or elliptical plains, and the most remarkable amongst these, {136} namely, that of Monastir, has been compared by Grisebach, the geologist, to one of those huge crater lakes which the telescope has revealed to us on the surface of the moon. In most of these plains we meet with swamps or small lakes, the only remains of the sheets of water which at one time covered them. The most extensive of these lakes is that of Ostrovo. The Lake of Kastoria resembles the filled-up crater of a volcano. In its centre rises a limestone hill joined to the shore by an isthmus, upon which is built a picturesque Greek town. According to Viquesnel and Hochstetter, traces of glaciers do not exist in any of these ancient lacustrine basins, or on the flanks of the mountains. It is certainly remarkable that whilst other European mountains—as, for instance, the Vosges and the mountains of Auvergne—have passed through a glacial epoch, the far more elevated Peristeri, Rilo Dagh, and Balkan, under about the same latitude as the Pyrenees, should never have had their valleys filled by moving rivers of ice.[38] All the large rivers of European Turkey belong to the Bulgarian regions of the Balkan or Hæmus. In Bosnia there are merely small parallel rivers flowing to the Save; Albania has only turbulent torrents forcing their way through wild gorges, like the Drin; but the Maritza, the Strymon or Karasu, the Vardar, and the Inje Karasu, which descend from the southern flanks of the Balkans, or originate in the crystalline mountain masses of the Rhodope, are large rivers, which bear comparison with the tranquil streams of Western Europe. As yet we know but little about their mode of action. The volume of water discharged by them has never been measured, and they are hardly made use of for purposes of navigation or irrigation. They all traverse ancient lake basins, which they have filled up gradually with alluvium, and converted into fertile plains. This work of filling up still goes on in the lower portions of these fluvial valleys, where extensive marshes, and even gradually shrinking lakes, abound. One of these lakes, the Takhino, through which the Strymon flows before it enters the Ægean Sea, is said to be the Prasias of Herodotus, and its aquatic villages were no doubt similar to the pile dwellings discovered in nearly all the lakes of Central Europe.