The retrocession of the strand line in Hokuriku district has been well known to the people living there, while the discovery of submerged forest at Uozu has proved the subsidence of the ground. The excavation of the submerged forest has attracted the attention of not only scholars but many people, and the Ministry of Education has designated it as special natural monument.
Soon after the discovery of the submerged forest, it was found that there was a submarine forest at the coast of Uchidegahama. It is concluded, therefore, that one of the causes of the retrocession of the strand line along the coast in the eastern half of Toyama Bay has been the subsidence of the ground.
Dr. T. Wakimizu thinks that the cause of the subsidence is the fault, but the writer believes it to be the block movement.
Hojozu Lagoon is also supposed to have submerged judging from the peat found around the lagoon, and the writer has concluded that the beach line was once far in the offing.
As the result of the revised levelling to prove that the block movement is the cause of the retrocession, it has been found that the land along the coast of the eastern half of Toyama Bay subsides 2 or 3 mm a year, on an average, while that of the western half of the bay up-heaves.
It has also been proved that the eastern half of the bay belongs to the large scale block of Tateyama, while the western half is rather a small block ranging from Himi to Noto, and that the block of Futagami are moving.
As the main cause of the retrocession of the strand line was the wave erosion, especially, Yorimawari wave, the Beach Line Survey Association of Toyama Prefecture has been organized to find out what to do with it. The writer has been appointed to head geological department and made a survey of the district on its geology, geography and historical facts with the help of fourteen people who have interest in it.
We have found that the districts of Ueharamura, Namerikawa and Shinminato have suffered heavily from the wave erosion.
In trying to find out the cause, we have obtained the following results. About Ueharamura district, we have found that the amount of the sand and pebbles supplied by the Kurobe River has decreased since the mouth of the river was moved to the west, and that the tide flows from the east to the west along its coast. About Namerikawa and Shinminato, we have found through the study of old maps and old records a striking fact that the strand line along the district has retroceded 1 meter a year, on an average.
Recently, a research has been made on the submarine canyon based on the study of late Dr. R. Tayama, and it has been proved that the canyon has much connection with the development of waves and that it is the result of subsidence of ground in recent geological age, that is to say, the canyon is the remains of an old valley. Although this has no direct connection with the theme of my study, I think it is adequate to refer to it.
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