Japanese National Railways has been carried out a Series of submarine geological surveys at the Akashi Straits where interisland-through rail-and road-way are proposed. According to the results hitherto obtai.ned, there develop widely gravellous formations (from latest-Tertiary to earliest-Quaternary) underlain by Miocene group (mainly sandstone with some shale and conglomerate) or older granite.
So, the author presents an every-5m countour map of these underlying groups based on Sparkers records. By this map (Fig. 3), thickness of the gravellous beds and relief of. basement rocks are numerically illustrated, and its accuracy is thought to within±5meters examined from all the standpoints of concerning factors.