(1) Total length (measured on plan survey map of Cad)

• Viewing route: approx. 245 m

• Closed area: approx. 325 m

• Total length: approx. 570 m

• Based on survey results, stairways and ramps are measured in plane projection distance, measured on Cad.

 

(2) Cave structure

• Complex planar shape.

• Complex cross-sectional configuration. (3-layered structure with complex intricacies.)

• It can be said that the surveying and construction techniques are very sophisticated.

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(3) Soil type and geology

• Cenozoic Era - Quaternary Period - Middle Pleistocene Epoch (Fig 1) - Sagami Group - Naganuma Formation [1] (formed between about 700,000 and 150,000 years ago. Marine sediment )

[1] Naganuma Formation: 

The lowest part of the Middle Pleistocene Epoch Sagami Group, which is formed along the Kashio River in Naganuma-cho, Sakae-ku, Yokohama, at the northern end of the Miura Peninsula.

( Reference: Shogakukan Nippon Encyclopaedia (Nipponica)).

• Wet conditions must be sustained. (Results of sample experiments, Saitama University).

 

(4) Plastering hypothesis.

• The tunnels have a clean, straight rectangular cross-section (Fig. 2). From the viewpoint of the construction technique of excavation, it is difficult to continue excavating the same rectangular cross-section shaped by direct excavation of the cave tunnels for a long length of time. It is possible that the rectangular cross section is finished neatly by plastering.

(Even in modern tunneling, internal shaped sections are done after rough excavation.)

• There are no shells (xenobiotic) found in the relief area.

(The formations here contain many fossil shells. It can be suggested that the relief was sculpted after plastering to create a canvas.)

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(5) Cave environment.

• Temperature and humidity are almost constant throughout the year.

(cool in summer and warm in winter; the temperature is between 16°C and 18°C, but has been rising in recent years).

• Water seeps out from everywhere.

(Groundwater)

• The soil is comparatively soft, but hard when compressed with water.

(Characteristics of the Naganuma Formation)

• When there is heavy rainfall, the inner ceiling often becomes stripped.

(There is a possibility that water channels have already formed.)

 

(6) Religious art.

• It can be considered that the modeling was done by experts in religious art.

• The reliefs can be considered to be the work of highly skilled wood carvers.

(Can be considered to be similar to the technique of transom openwork in wooden architecture.)

• Some of the relief sculptured after the middle of the Edo period.

• On the wall of the dome of the 88 sacred sites in Shikoku, there is a inscription "Bunkyu 2-nen" (completed in 1862).

(Bunkyu 2 = 1862, Ikamugi Incident, Sakamoto Ryoma's defection from the clan).

• Need to investigate detailed records and inscriptions on all reliefs.

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(7) Function.

• Training cave for Shingon esoteric Buddhism. (Still a training site for monks at present.)

• Sacred sites that are copies of the three major sacred sites in Japan (100 Kannon statues in Saigoku, Chichibu and Bando).

• Sacred sites that are copies of the 88 Kannon statues of the Shikoku Pilgrimage.

• Copy mausoleums of the 'Koyasan Okunoin' (tombs of Kobo Daishi at Koyasan in the Shingon sect of Buddhism).

• By walking through this cave, you will have toured all the religious sites in Japan.