At the same time, much of the low plains of modern-day northern France and northern Germany were inundated by an inland sea, where the chalk was deposited that gave the Cretaceous Period its name.
The Amazon, originally emptying into the Pacific, as South America rifted from Africa, found its exit blocked by the rise of the Andes about 15 million years ago. A great inland sea developed, at times draining north through what is now Venezuela before finding its present eastward outlet into the South Atlantic. Gradually this inland sea became a vast freshwater lake and wetlands where sediment flattened its profiles and the marine inhabitants adapted to life in freshwater. Over 20 species of stingray, most closely related to those found in the Pacific Ocean, can be found today in the freshwaters of the Amazon, which is also home to a freshwater dolphin. In 2005, fossilized remains of a giant crocodilian, estimated to have been 46 ft (14 m) in length, were discovered in the northern rainforest of Amazonian Peru.
In Australia, the Eromanga Sea existed during the Cretaceous Period. It covered large swaths of the eastern half of the continent.[A]
^Also in Australia the promise of an inland sea is often said to have been one of the prime motives of inland exploration during the 1820s and 1830s. Although this theory was championed by the explorer Charles Sturt, it enjoyed little support among the other explorers, most of whom were more inclined to believe in the existence of a Great River which discharged into the ocean in the north-west corner of the continent.
^Šliaupa, Salius; Hoth, Peer (2011). "Geological Evolution and Resources of the Baltic Sea Area from the Precambrian to the Quaternary". In Harff, Jan; Björck, Svante; Hoth, Peter (eds.). The Baltic Sea Basin. Springer. ISBN 978-3-642-17219-9.
A mediterranean sea is, in oceanography, a mostly enclosed sea that has limited exchange of water with outer oceans and with water circulation dominated by salinity and temperature differences rather than winds. The eponymous Mediterranean Sea, for example, is almost completely enclosed by Europe, Asia, and Africa.
A body of water, such as a river, canal or lake, is navigable if it is deep, wide and slow enough for a vessel to pass or walk. Preferably there are few obstructions such as rocks or trees to avoid. Bridges must have sufficient clearance. High water speed may make a channel unnavigable. Waters may be unnavigable because of ice, particularly in winter. Navigability depends on context: A small river may be navigable by smaller craft, such as a motorboat or a kayak, but unnavigable by a cruise ship. Shallow rivers may be made navigable by the installation of locks that increase and regulate water depth, or by dredging.
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