The most common image of the Soviet North is undoubtedly Siberia, a territory occupying a vast area between the Ural Mountains in the North and the Pacific Divide range in the East and stretching from the Arctic Coast in the true North to the borders with Mongolia and China in the South. In spite of the harsh, highly fluctuating climate (with mean temperatures of minus 68 degrees Celsius in January to plus 35 degrees in July), there has been a steady influx of Siberian settlers since the second half of the 19th century, particularly after the construction of the Trans-Siberian railway (1891-1905). Following the October revolution, a massive exploitation of the rich natural resources led to a further increase in population - topping 25 million in the 1970 census. A place of exile and hard labour both under the Czarist Russia and the Soviet regime, home to taiga and tundra, and a territory of no fewer than seven linguistic groups, Siberia has long embodied the idea of the last frontier. Illustrated children's books such as Mikhail Ruderman's Severnyi mai (Norther May, 1933), V taige (1933) or Pokrovskaia's Pro olenei i detei, pro sobak i gusei (Of reindeer and children and dogs and geese, 1934) drew on the rugged beauty, fascinating fauna and the many adventures of life in the North. Mindlin's Krasin vo l'dakh (The Krasin in ice, 1930) makes use of an imaginative constructivist typography in representing the accumulating sheets of ice that prevent the Krasin ship from advancing.