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Page:Provincial geographies of India (Volume 1).djvu/75

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GEOLOGY AND MINERAL RESOURCES

main Indian coal period; they thus enable us with great precision to fix the position of the fresh-water Gondwanas in comparison with the marine succession.

Spiti.— With a brief reference to one more interesting patch among the geological records of this remarkable region, space will force us to pass on to consideration of minerals of economic value. The line of snow-covered peaks, composed mainly of crystalline rocks and forming a core to the Himalaya in a way analogous to the granitic core of the Alps, occupies what was once apparently the northern shore of Gondwanaland, and to the north of it there stretched the great ocean of Tethys, covering the central parts of Asia and Europe, one of its shrunken relics being the present Mediterranean Sea. The bed of this ocean throughout many geological ages underwent gradual depression and received the sediments brought down by the rivers from the continent which stretched away to the south. The sedimentary deposits thus formed near the shore-line or further out in deep water attained a thickness of well over 20,000 feet, and have been studied in the tahsil of Spiti, on the northern border of Kumaon, and again on the eastern Tibetan plateau to the north of Darjeeling. A reference to the formations preserved in Spiti may be regarded as typical of the geological history and the conditions under which these formations were produced.

Succession of Fossiliferous Beds.— In age the fossiliferous beds range from Cambrian right through to the Tertiary epoch; between these extremes no single period was passed without leaving its records in some part of the great east-to-west Tibetan basin. At the base of the whole succession there lies a series of schists which have been largely metamorphosed, and on these rest the oldest of the fossiliferous series, which, on account of their occurring in the region of snow, has been named the Haimanta system. The