Both are composed of layers (sometimes four miles thick) of ancient metamorphic (heat-altered) rocks—gneisses (metamorphic rocks separable into thin plates), quartzites, and schists—that are between 570 and 395 million years old.
The western slope of the Urals is composed of middle Paleozoic sedimentary rocks (sandstones and limestones) that are about 350 million years old.
In the north, intensive weathering has resulted in vast “seas of stone” on mountain slopes and summits.
The lower The rock composition helps shape the topography: the high ranges and low, broad-topped ridges consist of quartzites, schists, and gabbro, all weather-resistant.
About 280 million years ago there arose a high mountainous region, which was eroded to a peneplain.The eastern slopes, on the other hand, have fewer karst formations; instead, rocky outliers rise above the flattened surfaces.Broad foothills, reduced to peneplain, adjoin the Central and Southern Urals on the east.The rivers on the western slope carry more water than those of the east, particularly in the Northern and Nether-Polar Urals; the slowest rate of flow is on the eastern slope of the Southern Urals, reflecting intense evaporation as well as low precipitation.In winter the rivers freeze for five months in the south and for seven months in the north.