@article{oai:rekihaku.repo.nii.ac.jp:00000348,
 author = {春成, 秀爾 and Harunari, Hideji},
 journal = {国立歴史民俗博物館研究報告, Bulletin of the National Museum of Japanese History},
 month = {Mar},
 note = {application/pdf, The Age of the Nishiyagi Formation
With regard to the age of the Nishiyagi Formation, ITIHARA'S view that a valley which had been eroded out during the Riss Glaciation was then buried during the Riss-Wurm Interglacial to from the Nishiyagi Formation is convicing.
A depositional cycle of a river sand and gravel layer→marine clay layer→lake clay layer and sand and gravel layer was ascertained by this investigation, and the existence of a single marine transgression was reconfirmed. And now the question becomes, to which of the Pleistocene transgressions does this correspond?
From a topographical standpoint, if the Yamatedai Terrace (about 60 meters in height) above the sea cliff at Nishiyagi was formed by the marine transgression at the Riss-Wurm Interglacial maximum at approximately 125,000 years B.P., then it can be inferred that the Misaki Marine Transgression of the South Kanto District (at approximately 60,000 years ago) was responsible for the formation of the Nishiyagi Terrace.
According to paleomagnetic observations, a major variation in polarity can be discerned between the middle and lower parts of layer IV. The pattern resembles that of the Ina I Excursion of about 60,000～70,000 years B.P.
A ¹⁴C estimate was obtained from the worked wood plank. The result was an estimate of 52,000 +10,000 -4,000 years B.P.
Additionally, an elephant tusk collected from the sand and gravel layer at the base of the Nishiyagi Formation at a point 2.15km south-east of the excavation site yielded a date of 90,000～55,000 years B. P. when tested by aminoacid racemization.
Combining the views and estimates provided by geologic and topographic methods, we deduce that Layers IV and V of the Nishiyagi Formation can be dated to a minor interglacial of the early phase of the last major glaciation at approximately 60,000-70.000 years B. P.
The Problems of the Artifacts and the Site
The wooden artifact from Nishiyagi has an aspect which suggests that the maker had a deep knowledge of wood as a raw material, similar to that which can be seen in the selection of raw lithic material for stone tools.
This speaks of much accumulated experience with the manufacuture of wooden implements even during the Early to Middle Paleolithic period. Hereafter it will be necessary to pay strict attention to the discovery of wooden artifacts when layers of peat and layers containing plant remains are encountered during excavations.
The flake tool which was collected from the Nishiyagi Formation Layer V in 1965 can be assigned to the Second Stage middle phase of OKAMURA Michio's chronology due to both its estimated age of 600,000 years and the details of its shape. It can be considered to correspond to the industries from the surface of Layer 10 at Babadan in Miyagi Prefecture and from the Gongenyama site in Gunma Prefecture. In Western Japan stone tools which date to the period prior to 30,000 years B. P. come only from the Sozudai site in Oita Prefecture and the Fukui cave in Nagasaki Prefecture. Also the stone tools from Nishiyagi clearly are from a period older than the stone tool industries of the Kinki and Setouchi District which are manufactured by such particular methods as the Setouchi technique and that of the Kō type knife. However, only two artifacts were recovered from the Nishiyagi Formation and further data is needed.
The excavation location at Nishiyagi was not a place where people lived long ago. Rather, the material there was deposited by the Old Nishiyagi River. The original site can probably be supposed to have been located several kilometers north of the excavation site.
Some clue as to where to search for human sites from this period has been awaited due to the discovery of human artifacts in the Nishiyagi Formation, but the conditions of the finds, the fact that they were included in the alluvial deposits of a river, is very different from other sites so far discovered. It seems for now there is no other way to begin searching for other remains of this period in the Kinki region that to conduct walking surveys searching sand and gravel layers very carefully. For such searches, layers from which fossils of NAUMAN'S elephant and plant remains have been discovered offer promising clues. In any case. without actively digging into geological layers which are possibly of the desired antiquity it will be difficult to find human sites in the Kinki region which are older than 30,000 years B. P.
The problems of the Akashi innominate
Another important goal of this excavation was to examine the Nishiyagi formation to determine whether or no tit has appropriate mineralogical and hydrological conditions for the preservation and/or fossilizaton of bone such as the Akashi innominate. The investigators had hoped to find some bone from the Nishiyagi Formation during the excavation to provide a basis for comparison with existing photos of the Akashi innominate for similarities of preservation condition. This would have allowed an assessment of the age of the find independent of morphological considerations. No bone was encountered during our excavation, unfortunately. Additionally, although he cautions us that a single chemical test is insufficient as the basis for a final conclusion as to the layer's preservation capabilities, MATSU'URA'S analysis of the pH of sediments from Nishiyagi layer V gives indications that condition for bone preservation here may not be good.
However, our investigation revealed that Layer V (from which the Akashi innominate is supposed to have come) is a wet sand and gravel with clay layer under lain by hard clay. Many plant remains in good condition were recovered from this layer. Therefore it is reasonable to conclude that it is entirely possible for bone to be anaerobically preserved within this layer. So, while it has been determined that layer V does have appropriate conditions for the preservation of bone, morphological studies, such as those of ENDO and BABA, and DODO in this volume, support the claims that the Akashi innominate is that of a modern Japanese. This excavation has not yielded results which allow us to draw any final conclusions about the authenticity of the Akashi innominate.
However it has provided some basis for claiming that the Nishiyagi Formation is approximately 60,000-70,000 years old. Therefore we hope to see future studies investigating whether the morphological characteristics of the Akashi bone could conceivably be those of a hominid of 60,000-70,000 years ago. We believe that this excavation has been valuable both for bringing new data to light and for indicating a clear direction for future research in Quaternary studies in Japan.},
 pages = {291--304},
 title = {22. 西八木海岸発掘調査の意義（総括）},
 volume = {13},
 year = {1987},
 yomi = {ハルナリ, ヒデジ}
}