A preliminary reconstruction of the geology of Middle-earth is attempted, utilizing data presented in text, maps and illustrations by its arch-explorer J.R.R. Tolkien. The tectonic reconstruction is developed from earlier findings by R.C. Reynolds (1974). Six plates are now recognized, whose motions and collisions have created the mountains of Middle-earth and the rift structure down which the River Anduin flows. The stresses involved in the plate collisions have produced patterns of faults, whose lines have determined the courses of the other rivers and the occurrence of the richest ore deposits. However, the time of Bilbo and Frodo is a period of tectonic quiescence. Volcanic activity is at a minimum and confined to four “hot-spots”, all at some distance from plate margins, while seismic activity is minor. Tolkien’s paintings, in particular, show how glacial and riverine erosion have shaped Middle-earth’s topography.

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