The Toyama Plain was constructed by the compound-alluvial fan, but some parts of it are the Delta plain with small lagoons (Fig. 1). The writer surveyed the landforms and the shell-mounds of the neolithic age in this plain, and analysed underground structures according to the data which were gotten by boring and physical prospectings. The results may be summarized as follows:
1. Delta of the Toyama plain were affected by the transgression in the early alluvial age and the shallow imbayments were formed in a part of the delta. The delta plain in the Hokuriku districts can be understood to be similarly as the Toyama plain.
2. The climax stage of the transgression in the Toyama plain corresponded to the early Jyomon age or more older, namely earier than the transgression attacked the Kwanto plain.
3. The crustal movements of this region had happended so as to increase the inclination. The distribution of river terraces caused by the eustatic movement were not always remarkable, and the affection of the high sea-level were limited to the lower parts and near the coast.
4. After that, the river ran through the depression made by the faults and the low land between old fans and had constructed new alluvial fans before the late Jyomon age.
5. There are fossil valleys beneath the new alluvial fan made by the Jinzu River. Probably theyconnect with the submarine canyon at the mouth of this river.
According to the facts above mentioned, the writer tried to make the chronologibal table of the geomorphological development of the Toyama plain (Table 1).
