This paper shows that, in deep-sea drilling, the distribution of shallow face materials becomes shallower with each era subsequent to the middle period of the Mesozoic. This is said to be caused by various phenomena including: increas,e in the amount of seawater in the Mesozoic/Tertiary, conversion of continental crust to oceanic crust, deepening of the ocean floor due to plate cooling, and subsidence of the ocean floor accompanying rifting on the passive continental margin. However, these theories have difficulties in terms of paleobiology, physical chemistry or paleogeography, and a plausible explanation cannot be obtained. We believe that what is happening on the ocean floor deeper than items where the shallow face materials of an older era have a young age, is that in situ shallow face materials are brought to the ocean floor together with the era, due to underplating at the ocean floor of basalt magma of the Mesozoic and Cenozoic. Sea level will rise with increasing ocean floor, the location of the original floating point is brought into deep steadily over time.