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Limestone is an example of Sedimentary rocks. Limestone is a carbonate sedimentary rock that is often composed of the skeletal fragments of marine organisms such as coral, foraminifera, and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).

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The difference between the equatorial and polar diametres of the earth is about 42 km. Due to spinning motion the Earth's equator area bulges out. There is difference of about 42 Kilometers between diameter at equator and at poles.

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The inequality between day and night becomes greater or more marked as one travels from Equator to Poles.

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The Labrador Current is a cold current in the North Atlantic Ocean which flows from the Arctic Ocean south along the coast of Labrador and passes around Newfoundland, continuing south along the east coast of Nova Scotia.

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The Suez canal lies on one of the world's largest of trade routes connecting Europe and Far East. The canal separates the African continent from Asia, and it provides the shortest maritime route between Europe and the lands lying around the Indian and western Pacific oceans. It is one of the world's most heavily used shipping lanes.

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The major cause of the decrease in population of rural areas as compared to the towns is Migration of people from villages to the urban areas in search of better facilities and employment.

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Trans-continental railways have played an Important role in Development of resources in the interior of continents. The development of railroads was one of the most important phenomena of the Industrial Revolution. With their formation, construction and operation, they brought profound social, economic and political change to a country only 50 years old.