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Monday, February 26, 2007

now guys lets move on to cretaceous period with me irvin

The Cretaceous Period - 1
The Cretaceous Period of the Mesozoic Era: 146 to 65.5 million years ago

In 1822 the Belgian geologist D'Omalius d'Halloy gave the name Terrain Cretace, for the chalk and rock outcrops of the Paris Basin, and for similar deposits in Belgium and Holland and traceable also from England eastward into Sweden and Poland.
This term "Cretaceous" "chalk-bearing" (from Creta, the Latin word for chalk) later came to be used. The famous White Cliffs of Dover, are typical of this rock formation. Extensive chalk deposits were laid down in Europe and parts of North America during this period. The chalk itself is actually formed from the shells of countless micro-organisms.
William Smith had previously mapped four strata between the lower clay (= early Tertiary) and the "Portland Stone" (= late Jurassic), namely White Chalk, Brown or Grey Chalk, Greensand, and Micaceous Clay or brick earth (later referred to as Blue Marl or Gault). In 1822 Conybeare and Phillips arranged these in two groups, the Chalk and the earlier strata, a division that has remained to the present day. In 1841 Leymerie introduced the term Neocomian for the lower division. Senonian was coined by d'Orbigny in 1842 for the later Cretaceous. The name "Gallic" has also been used for times that do not fall conveniently into either of the above two categories.

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