The oldest rock species of Podolia are the granite-gneisses, which were folded and disturbed in pre-cambrian times. The lines of the folds and breaks stretch principally north to south. Granite composes the rocks of the Dniester rapids near Yampol and the numerous rapids of the Boh River, in whose rocky vale this primitive rock formation appears distinctively. On the granite base, almost horizontally, slightly turned toward the southwest, lie dark slate and limestone, upper silurian at first in West Podolia, then the devonic layers, of which the old red sandstone attracts the eye most of all, because of the dark red coloring which it gives to the steep walls of the Podolian cañons. These are followed by chalk layers, and, last of all, by recent tertiary formation whose gypsums form picturesque groups of rocks on the heights of the Yari walls. In the mighty gypsum stores of Podolia may be found many a large, beautiful cave, with wonderful alabaster stalactites. All tributaries on the left side of the Dniester, beginning at the Zolota Lipa, flow into yari-cañons of this sort. The most beautiful and magnificent is the cañon of the Dniester, whose walls often exceed a height of 200 m. It cuts thru the high plateau in adventurous windings, every curve revealing new, beautiful prospects over the high, concave, steep edge, torn by ravines, and the gently rising [42]convex banks. In deep gorges the yari of the tributaries open into the yar of the main stream. Between the defiles stretches the flat, hardly undulating plain. In the summer only endless waving grain-steppes present themselves to the view of the traveler, only here and there a little wood appears on the horizon, or a lone farm. Suddenly the wood seems to end, the traveler is confronted by a deep, steppe-walled valley, down the sides of which climbs the road. And below, on the silvery river, amid the green of the orchards, lies village after village. The further to the east, the more frequent do the yari become, and the balkas (gorges) similar to them but smaller; yet these are not so deep and picturesque. In the regions of Tiraspol Ananiv the entire plateau surface is very profusely cut by these defiles. In the district of Ananiv the balkas take up one-seventh of the entire surface. The plateau is cut up by these water crevasses into innumerable narrow fens. The balka, like the yar, owes its existence to the erosive activity of flowing waters. On the Dniester we see, on both sides of its deep yars, great masses of old river boulders, which lie on the summit of the plateau beneath the thick cover of loam. They are boulder deposits of the pre-glacial Dniester. Later, when the recent raising of the Ukrainian plateau group began, and it occurred with particular force in the Podolian Plateau, the rivers cut in, and in the course of thousands of years formed their present picturesque defiles.