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-8- <br />C~ <br />the end of the Albian. <br />The Late Cretaceous of the area shows three facies related to <br />environment: a grey or black shale of a shallow marine environment <br />as seen in the Mancos and Lewis Formations; tan or buff sandstone <br />facies of transitional and nearshore depositional environment seen <br />in the Fox Hills Formation; grey clays and tan lenticular, often <br />coal bearing sandstones suggesting swamp, lagoonal, and coastal <br />plain environments which are preserved in [he Mesaverde Group (in <br />the study area composed of the Iles and Williams Fork Formations). <br />All of these environments were contemporaneous, with marine conditions <br />dominating towards the east and continental towards the west. Between <br />these two extremes there is a complex intertonguing of the facies <br />caused by the shifting shoreline. The dominant direction of these • <br />shifts was slowly to the east starting at about the Early Campanian. <br />This regression was not a smooth steady process but involved a series <br />of minor transgressions and regressions. By Maes[richtian times the <br />last major advance of [he Sea was concluded and the overlying sediments <br />were strictly continental. <br />The Late Cretaceous sea was known to be filled with many life <br />forms, such as Inoceramus, Ostrea, Baculites, fish, and marine reptiles. <br />Along the beach and coastal plain turtles, crocodiles, dinosaurs, and <br />tiny mammals dwelled among sassafras, sequoia, palm, and many other <br />plants that still exist today. However, in northwestern Colorado the <br />only well studied fossils are the invertebrates as they are valuable <br />tools for stratigraphic correlations. Rather extensive works for both • <br />