The
Western Interior Seaway (also called the
Cretaceous Seaway, the
Niobraran Sea, and the
North American Inland Sea) was a large
inland sea that existed during the mid- to late
Cretaceous period as well as the very early
Paleogene, splitting the continent of
North America into two landmasses,
Laramidia to the west and
Appalachia to the east. The ancient sea stretched from the
Gulf of Mexico and through the middle of the modern-day countries of the
United States and
Canada, meeting with the
Arctic Ocean to the north. At its largest, it was deep, wide and over long.