The oldest rock layer of the Rostoche is the chalk-marl. Above it lie, in almost undisturbed horizontal layers, miocene limestone, sandstone, clay, sand, Diluvial loam, while sand and broken stone with many boulders, which are of unmistakable northern origin and were transported by glaciers and streams of the ice period as far as the southern part of the Rostoche, form a heavy cover everywhere. The ground is not very fertile, sand and marl soil being particularly wide-spread.
The northern part of the Rostoche, beyond the Tanva valley, is a broad, slightly undulating plateau, which, in its highest part, reaches a height of only 340 m. The western edge of the plateau is distinct and steep and declines in places 100 m. to the low country of the Vistula. Toward the north the plateau surface declines very gradually and merges almost imperceptibly into the plain of the Pidlassye. The river valleys, as those of the Buh, Vepr, are broad, flat and marshy.
The geological constitution of the northern Rostoche is almost entirely similar to that of the southern part. Its soil cover, too, is not very fertile, and only great woods have survived, especially in the districts of the old morainic sand and loam. Only in the neighborhood of the Pidlassye does the soil become more fertile. For the configuration of surface of the Rostoche, the recent post-glacial raising of the ground has also been of great significance, altho here it was not nearly so intensive as in Podolia.
The Volhynian Plateau extends over a broad space between the Buh in the west and the Teterev in the east, between the swampy plain of the Polissye in the north and the Dniester-Dnieper watershed and the upper Boh valley in the south. The Volhynian Plateau does not [[47]]possess the compactness of the Podolian or Rostoche Plateau. The swampy lowland of the Polissye extends along the rivers into the heart of Volhynia, thereby dividing its plateau country into several sections of different size. Likewise, the inner structure and geological constitution of Volhynia is variable. Western Volhynia, situated between the Buh and Horin Rivers, has a sub-layer of chalk marl, which is capped in places by layers of clay and sandstone and limestone of recent tertiary date. Eastern Volhynia lies entirely in the region of the primeval Ukrainian Horst, whose plicate granite-gneiss sub-layer is covered by old tertiary deposits. In this tectonically disturbed region we meet with traces of early volcanic action. Near Berestovetz, Horoshki, etc., species of eruptive rock appear as signs of radical disturbances of the earth’s surface.
The surface soil of Volhynia is black soil only in the south. Beyond that we find here sandy soil, white earth and loamy soil, as signs of a one-time glacial covering and the action of fluvio-glacial waters. Many regions of loamy ground are rich in vegetable soil and not without considerable fertility.
The lowest part of the Volhynian Plateau is the western part, which lies between the broad, marshy, flat valleys of the Buh and the Stir. The slightly undulating, almost level plateau surface, which declines imperceptibly toward the Polissye, here just attains a height of 200 m., while the next section, between the Stir and the Horin is the highest part of Volhynia. As an extension of the above-mentioned northern edge of Podolia, the Kremianetz-Ostroh hill-country intrudes between the two rivers. Over 400 m. high, near the city of Kremianetz, it declines toward the north, a steep section torn by gorges and ravines. Near Dubno, the plateau is cut into a picturesque hill country with a maximum height of 340 m. The hills of Volhynia have steep, often rocky declines and flattened rocky peaks. [[48]]North of Rivne and Lutzk they finally begin to be lower and more rounded, then they dwindle to a flat billowy tract of land, until, at the borders of the Polissye, we see only an almost perfect plain.
Between the Horin and Sluch Rivers, the Volhynian Plateau becomes more uniform. Its surface is flat, and broad valleys of the rivers which flow toward the east, forming numerous ponds, part it slightly. Only in the south is a height of more than 300 m. reached; in the north, where the granite sub-layer appears everywhere, especially in river valleys, barely 200 m.
The eastern part of the Volhynian Plateau extends, at first, as a narrow plateau zone between the valleys of the Boh and the Teterev on one side and of the Sluch on the other. Then the plateau spreads out like a fan toward the north. At the source of the Boh and the Sluch, the plateau reaches a height of 370 m.; at the sources of the Teterev, 340 m. Here the surface is level, except that here and there low, gently-rounded hills arise. In the broad, northern part, the Volhynian Plateau becomes much lower and finally separates into individual plateau islands, as, for example, near Novhorod-Volinsky, Zitomir, Ovruch, which rise gently from the marshy lowlands.
The valleys of the Volhynian rivers, broad, flat, with gentle slopes and marshy bottoms, differentiate the Volhynian landscape most strongly from the Podolian. The Volhynian landscape presents a view of flat, wooded hills, slowly flowing streams between flat banks, marshes and marshy meadows, sandy ground—all signs of the proximity of the Polissye.
The Dnieper Plateau has the outlines of a longish, irregular polygon. On the northwest it is bounded by the rocky valley of the Teterev, on the southwest by the Boh River, on the south and southwest by the Pontian steppe-plain, on the northeast by the Dnieper River. [[49]]