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The actual boundaries of the Ruhr vary slightly depending on the source, but a good working definition is to define the Lippe and Ruhr as its northern and southern boundaries respectively, the Rhine as its western boundary, and the town of Hamm as the eastern limit. In the Middle Ages, local power was vested primarily in the counts (''Grafs'') of Berg, Mark and Cleves. The left bank of the Rhine was held by the Archbishop of Cologne. The Hellweg was an important trade route crossing the region from Duisburg to Dortmund and beyond as far as the rivers Weser and Elbe. The most important towns of the region were concentrated along the Hellweg. As a result of the Congress of Vienna the entire area came under the control of Prussia (the state had already gained possessions there). This event was almost concomitant with developments which would eventually make the region one of the most important industrial areas in the world. In 1946 the state of North Rhine-Westphalia came into being, centred on the Ruhr. Nowadays, its hitherto important coal and steel industries have drastically declined and the region is in a state of re-adjustment. ==Carboniferous period== During the Carboniferous Period, in the Paleozoic era, which began 360 million years ago and ended 300 million years ago, layers of slate, coal and sandstone were formed. 400 to 300 million years ago, new mountains were uplifted during the Variscan mountain-building period. In the Silesian, layers were deposited which become seams of coal over a period lasting millions of years . During this period there was a constant shifting between marshy conditions and overflowing seas such that the depositing of plant material and sediment from the sea results in the current situation of coal layers separated by stone layers. The main representatives of flora in the coal marshes were of the genus ''Lepidodendron'' and genus ''Sigillaria'', tree-like plants, which belong to the plant classification Lycopodiophyta. Members of both genus reached heights of up to 40 meters with a trunk diameter of over a meter. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「History of the Ruhr」の詳細全文を読む スポンサード リンク
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