ABOUT THE IWAJUKU ARCHEOLOGICAL SITE
World War II had only just ended when Tadahiro Aizawa, while passing along a narrow road in Iwajuku, happened to discover a small flake of obsidian. Aizawa noticed that this flake resembled a microlith (stone tool) and was buried in a layer of red soil. Afterwards, Aizawa continued to look hard for other stone tools or pottery fragments in the same area.
Tadahiro had expected to find Jomon Era pottery, which was, at that time, the oldest known culture in Japan. The red soil layer in the bluff along the road contained no pottery sherds at all, whereas the number of stone tools unearthed there continued to increase. At that time, it was commonly believed that humans did not inhabit Japan during the period in which the red layer was formed. As a result, Aizawa was puzzled by his discoveries.
Three years later, in 1949, Aizawa discovered a stone arrowhead in the same area. In order to confirm this discovery, it was necessary to excavate the red soil layer. This excavation demonstrated beyond a doubt that there were human settlements there at the time the red soil was deposited. Aizawaﾕs discovery became the means to establish the fact that humans had inhabited Japan more than 10,000 years ago. Following this discovery, many other Iwajuku Era sites were found all over the country.
Now, on the basis of the many archeological sites and artifacts discovered and much scientific research, a great deal has come to be known about Iwajuku Era culture. In fact, some sites have been dated as far back as 30,000 years ago. In all, more than 3,000 Iwajuku Era sites have been excavated in Japan.
In order to evaluate the Iwajuku excavations, Aizawa visited a professor at a university in Tokyo in 1949. Unfortunately, he was unable to convince the archeologist of his findings since it went counter to the thinking prevalent at that time. Aizawa did not give up, however, and made repeated visits. Finally, an archeologist at Meiji University, impressed by Aizawa's fervor, decided that his discoveries deserved further investigation. In order to confirm what was in the site, it was decided that it should be thoroughly excavated.
Three locations were chosen for excavation and were labeled "A", "B", and "C".The A site was located along a narrow road on the north side of the bluff. Digging here, they found many stone tools. These stone tools were buried between two distinct layers of soil. From this is was deduced that the Iwajuku Era itself could be further broken down into separate ages. The B site was located on the south side of the narrow road, opposite the A site. It was here that Aizawa had first excavated stone fragments and a stone spear. The C site was located about 1 kilometer to the northwest of the A and B sites. No stone tools were found in the red soil here, however, in the black layer of soil above it, they excavated many pottery fragments from the earliest Jomon period. Having discovered Jomon artifacts at C site, it became possible for them to confirm that the artifacts excavated from the lower layers of red soil had to date from a culture older than the oldest known Jomon culture.
These excavations proved that the culture represented at the Iwajuku site were from the Paleolithic Era; that there had been continuous human settlements in Japan, having crossed over from the Asian continent; and, that these settlements were indeed older than the Jomon Era.
Beginnings at Iwajuku Hills
Aerial photograph of the Iwajuku site
There are two prominent hills in Iwajuku; one is called Inariyama and the other Kotohirayama. Geological investigation of these two hills has determined that Inariyama is an extension of the south face of Mt. Akagi, whereas Kotohirayama is connected to the Ashio mountain range. This demonstrates that, in fact, Mt. Akagi was at one time a continuation of the Ashio mountain range. Over time, the Watarase River cut through the area, leaving behind these hills. At the same time that these hills were being formed by the cutting action of the river, it was also depositing earth and sand in other areas. The accumulation of this earth and sand formed the Omama Alluvial Delta.
The Kanto loam layers were subsequently deposited over the ancient rocks on Inariyama, Kotohirayama and the pebbles of the Omama Alluvial Delta, thus completing the geological formation of the area as we find it today. It is from within the Kanto loam layers that many stone tools have been excavated.
Although we do not see volcanic eruptions on Mt. Akagi today, sometime around 30,000 years ago there were repeated eruptions. In addition, major eruptions frequently occurred on Mt. Haruna and Mr. Asama. The loam layers found in this area represent the accumulation of volcanic ash from these repeated eruptions. This ash, called red soil, is located below the surface, and is several meters in thickness. It is believed that frequent volcanic eruptions prevented humans and animals from settling in the area.
Occasionally, there were huge explosions, resulting in the eruption of pumice stone and volcanic ash which accumulated all at once, so to speak, in large amounts. Such island-like accumulations of pumice can be found in the area. The soil is referred to as "Kanuma soil" and the pumice stones found there are often used in gardening. The pumice stones which came from a huge eruption on Mt. Akagi accumulated near Kanuma City in Tochigi Prefecture. Such pumice stones vary from volcano to volcano, exhibiting the special characteristics of each mountain and serve as a key in the dating process.
Further aids in dating Japanese archeological sites are the results of recent research regarding the geography of Kaitei Volcano, located on the northern part of Sakurajima in Kagoshima Prefecture. A tremendous eruption on Mt. Aira occurred there some 22,000 years ago which resulted in the formation of the well-known Shirasu Plateau. Volcanic ash from this eruption was carried in the wind as far as Gunma Prefecture. It is impossible to observe this volcanic ash with the naked eye, however, under a microscope, the volcanic ash can be clearly seen. Other pryoclastic explosions occurring on Mr. Aso, Mt. Daisen, Mt. Kiso'ondake have all contributed to the volcanic ash found in the soil strata of Gunma Prefecture.
It was thought that Iwajuku people probably survived by hunting for large game such as Naumann elephants (Palaeoloxodon naumanni) and bighorn deer. More recent excavations have indicated that, in fact, much of the Iwajuku people's nutrition came from less dangerous small game animals, nuts and berries, and fish. For the most part, they were hunters and gatherers.
To catch large game, they drove the animals into marshy areas to slow them down and then attacked with spears and arrows. The Iwajuku Period was much colder than it is now, thus trees and plants found only in higher elevations now were common in lower areas at that time.
Because of the presence of acidic volcanic ash in the soil strata, little other than stone implements has been discovered in Iwajuku excavations. Sites where these stone implements have been found are believed to be village settlements. The various forms of tools and implements excavated give some idea of the lifestyle during this period.
Recently, an Iwajuku site has been discovered near Hasami mountain in Osaka Prefecture. This site is a shallowly hollowed out circle, roughly 6 meters in diameter. Seven post holes have been excavated. Unfortunately, similar dwellings have not been found in Gunma. Despite minute research on a great many sites, no dwellings have been found, leading experts to believe that, for the most part, Iwajuku people lived in simple tent-like dwellings.
The various tools and implements excavated from Iwajuku sites indicate that they should be classed into the following age groups:
Iwajuku I Culture
Implements found in this layer are thought to have been used around 25,000 years ago. They are buried about 1.3 meters below the Kanto loam surface in a dark layer of soil which has been named the Iwajuku stratum. In all, some 29 tools composed of chert or shale have been excavated from this layer. Among the items excavated are polished stone axes (2), stone knives (3), a stone scraper, and a stone wedge for splitting bones, etc. In addition, some shaved stones (10) and broken pieces of stones used for shaping stone tools (10) were also found in this layer. More than anything else, this culture is characterized by the possession of the skill to form ground stone axes. No doubt these stone axes were used to fell trees and manufacture wooden items.
Iwajuku II Culture
Artifacts in this layer date back about 18,000 years and are found about 0.8 m below the loam in the upper portion of the Kanto loam stratum. Some 180 stone tool items have been excavated here. Chert tools predominate, however, obsidian, andesite, shale, Hornfels, agate, etc. were also used. Tools discovered include stone arrowheads (2), knifelike tools (8), tools for cutting wood (4), and stone flakes (136). The stone tools found in this layer are small in comparison with Iwajuku I Culture tools. In addition, stone fragments used in making stone tools (5) along with rough stones used in forming stone tools (25) were also found here.
Iwajuku III Culture
Although this era is referred to as Iwajuku III Culture, not much is known about it yet. Stone arrowheads predominate.
In Search of Obsidian
Obsidian is a form of stone which was frequently employed during the Iwajuku and Jomon Periods. This stone was probably used by prehistoric humans to form tools for the following reasons: 1. it was fairly easy to shape into tool implements; 2. it was possible to form very sharp points with it; and 3. it was durable. Obsidian is volcanic rock, sometimes referred to as natural glass. Because of the above mentioned properties, it was an excellent material for stone craft.
Obsidian, which can be used to form stone tools, is not found naturally in Gunma Prefecture. The closest locations to Gunma Prefecture where obsidian can be found are Wada Toge, Kirigamine and the Yatsuga hills in Nagano Prefecture. In addition, obsidian can also be found at Mt. Takahara in Tochigi Prefecture, Hakone in Kanagawa Prefecture, and Kozushima Island in the Izu group of islands. As a result, Iwajuku humans were limited in the locations from which they could obtain obsidian and had to travel to those locales or engage in exchange with others from those locales in order to procure it.
Origins of Iwajuku Humans
At present, it is believed that the human species originated in Africa sometime between 15 and 5 million years ago, evolving from other anthropoid species which include the great apes. The species evolved through Pithecanthropus, Homo erectus, Neanderthal and Homo sapiens. To date, the oldest known precursor is Australopithecus, an anthropoid species which dates back between 1.6 and 5 million years ago. Java man and Peking man (both Homo erectus) date to 1.6 and 2 million years ago. Neanderthal man, a European species, dates back to 200 to 300 thousand years ago. The European Cro-Magnon, the first Homo sapiens, is indistinguishable from modern humans and dates back to approximately 30,000 years ago.
The earth is now in the Fourth Geologic Epoch, which can be divided into the Pleistocene and Holocene Eras. The Pleistocene Era began somewhere around 1.8 million years ago and ended approximately 10,000 years ago. During this time, a glacial period tool place. This period was characterized by several extremely cold periods (Ice Ages) which were interspersed with warming periods (Wurm Ages). During the Ice Ages, the ocean level receded and the Japanese archipelago was connected to the Asian continent. During these periods, wooly mammoths, Naumann elephants, and other animals crossed over the land bridges, entering Japan from points both north and south. It is believed that humans also crossed over the land bridges in pursuit of these animals. The ancestors of the Iwajuku humans, no doubt, in ages long past, crossed over into Japan from the Asian continent.
The soil of Japan is highly acidic, and, for this reason, human skeletal remains from these periods have not been preserved. Nevertheless, in some more alkaline locations such as calcified rocks, there are some fossil remains. "Akashi man" is a famous example of this and is believed to have been Homo erectus. The skeletal sample, however, was destroyed in a fire in W.W.II before it could be positively identified. The oldest known human species found to date is "Minatogawa man", a Homo sapiens. The entire skeleton has been discovered, allowing for full identification. In addition, "Ushikawa man", (Neanderthal), "Mikkabi man", (Homo sapiens), "Hamakita man", (Homo sapiens) and "Kuzu'u man", (Homo sapiens) have also been discovered.
Recently, Early Jomon stone tools have been discovered at the Irinosawa Site in Niisato Village. Researchers continue to find extremely old stone tools dating back some 200 to 300 thousand years ago. As of yet, no Homo erectus remains have been found, however, the presence of Homo erectus in Japan is well within the realm of the possible.