Russian Empire Bolsheviks followed in 1918. The administrative boundaries of European Russia, apart from Finland and its portion of Poland, coincided approximately with the natural limits of the East-European plains. In the North it met the Arctic Ocean. Novaya Zemlya and the Kolguyev and Vaygach Islands also belonged to it, but the Kara Sea was referred to Siberia. To the East it had the Asiatic territories of the Empire, Siberia and the Kyrgyz steppes, from both of which it was separated by the Ural Mountains, the Ural River and the Caspian Sea — the administrative boundary, however, partly extending into Asia on
Baltica belt of the Timanide orogeny and overlain by Mesoproterozoic sediments. The margin became a passive margin facing an Ural Ocean in the Cambrian-Ordovician. The eastern margin stretches south through the Ural Mountains from the northern end of the Novaya Zemlya archipelago. The margin follows the bent shape of Novaya Zemlya which was caused in the Late Permian by the Siberian Traps. It is clear from Baltic endemic fossils in Novaya Zemlya that the islands have been part of Baltica since Early Palaeozoic, whereas the Taymyr Peninsula farther east was part of the passive margin of Siberia in the Early Palaeozoic.