The theory is explored that sea level has risen in the Arctic and Antarctic regions and fallen in the equatorial regions since the Cretaceous. Such change is considered to be in addition to, or in excess of, Pleistocene eustatic sea-level fluctuations or local isostatic adjustments of the crust. North America obviously shows submerged continental margins north of Puget Sound on the Pacific and New York on the Atlantic, and emerged margins southward. The Arctic region, aside from the Alaskan Coastal Plain, is submerged at least 500 feet in excess of upward Wisconsin isostatic adjustment to date. Both the east and the west coasts of South America are interpreted as emergent southward to Lat. 38°S, and progressively embayed and submerged from there to the southern tip (Lat. 55°S). Antarctica, if adjusted upward to pre-ice conditions, would still be considerably embayed, and its continental shelf is unusually deep. Isostatic adjustments incident to ice melting could not restore this shelf to the usual low-latitude depths. A charting of depths of the outer margin of the continental shelves from the Arctic along both sides of North America and South America to Antarctica reveals an outer shelf margin at a depth of 500 to 600 feet in the low latitudes and a progressive deepening of this outer margin to 1,300 or more feet in the Arctic and Antarctic regions. Africa is entirely in the low latitudes and its generally stable east and west coasts are believed to have become emergent during Cenozoic time. The outer margin of the shelves is at a depth of about 600 feet. No trend could be noted. The west coast of Australia is also generally one of Cenozoic emergence southward to Lat. 35°S; from here to the continent's southern limit in Tasmania the coast is submerged. If these observations are correct, the uniform worldwide nature of submergence and emergence of the continental margins precludes local or even regional tectonism as a cause. It can only be postulated that sea level has changed, downward in the low latitudes and upward in the high. Worldwide survey of the constitution of the continental shelves is probably necessary to prove or disprove this theory. Account must be taken of vertical movement of coastal areas by local tectonism, and of eustatic movements of sea level due either to glacial stages or to broad vertical movements of the ocean floors. Ocean expansion in the polar and contraction in the equatorial regions might conceivably have culminated in the Pleistocene glacial stages. The cause of such a shift in sea level would appear to be a slowing rate of rotation of the earth. There is little doubt that the length of day has been increasing over the past twenty centuries, and this rate, if extrapolated back 100 million years, would yield an angular velocity about 1/50 faster then than now. The supposition would be that the solid earth with finite strength has lagged in adjustment to slowing rotation, but the oceans have responded immediately.