The writers observed the submarine structure from the contour line map of the base of the Alluvium and the geological cross sections from boring data of 21 points in Tokyo port. They conclude as follows. 8 valleys are traceable as is shown in Fig. 1. They are considered as former erosional valleys, and they merge into one river system off Haneda. There are two terraces at the levels of -10m and -30m. These two Surfaces extend in long and narrow shapes. The -10m Surface and the -30m Surface are devided by the Asakusa-Fukagawa line. The deposits in this area mainly consist of sand, mud and clay. The upper sand formation scattered off Haneda and Fukagawa, are seemingly the delta deposits formed by the Arakawa and the Rokugo-gawa. The N value by the standard penetration test is very different by formation (Table).