The widespread Late Cretaceous transgression is one of the best documented episodes of world-wide continental submergence, yet its cause or causes remain elusive. Subsidence of continents, rise of sea level, or a combination of both are plausible hypotheses, but testing them is difficult because the effects of sea level rise and continental subsidence are similar— that is, transgressive deposits. One solution to the problem can be derived from comparison of actual sediment thicknesses with those calculated as possible from a maximum sea level rise. A sea level rise of about 310 m is required to flood the area submerged in Late Cretaceous time. However, the maximum thickness of a transgressive deposit produced by a 310-m rise of sea level is only about 700 m. In North America, nearly 50 percent of the area flooded during Late Cretaceous time contains strata thicker than 700 m; this indicates the important role of continental subsidence during the Late Cretaceous submergence.