抄録
The Kumano Coastal Mountain is a range extending south-southwestwand from Ôdaigahara-san, one of the highest points in the Kii Peninsula.
The Tertiary .history of this. mountain region is as follows:
1) Transgression of the Miyai Sea, Probably. at the beginning of the Oligocene, the Miyai Sea began to transgress slowly northwards over area of Mesozoic strata of complex structure. While the sea was encroaching upon certain parts of the land not so highly subdued, other regions situated far more inland were still undergoing reduction and were worn down nearly to a peneplane when the sea-reached there.
2) Post-Miyai Tectonic Movement. After the transgression of the Miyai Sea, the area was subjected to a great disturbance, such as severe block movements and foldings.
3) Post-Miyai Erosional Stage. After this period of disturbance an era of great. quiet prevailed, and for a long time the forces of destruction vigorously attacked the surface of the land and reduced it gradually to a low and rolling land.
4) Extrusion of the Kumano Acidic. Igneous Rocks, probably in the Miocene.
A) The First Activity. At last the long period of quiet drew to a. close and lava flows of biotite felsoliparite and granophyric biotite liparite extruded through a. large fissure and covered a part of the Post-Miyai erosion surface.
B) The Main Activity. Then persemic garnet-bearing biotite liparite intruded and partly extruded from a batholithic mass of acidic magma. During this time. the mass of magma was approaching the surface of the area and at last, extruded, shattering the roof rocks into pieces which were swallowed up in the molten magma, and it flowed over a rather wide area. This type of extrusion of biotite granite 'Porphyry and persemic liparite seems to be a kind of the “extrusion by de-roofing, ” as Prof. R. A. Daly calls it. Intrusion of dikes of granite porphyry and persemic liparite took place, accompanying the extrusion by de-roofing of the main mass, and also after it.
5) Post-Kumano Erosional Stage. The history of the district after the extrusion of the Kumano Acidic Igneous Rocks is as yet almost a blank, for throughout the whole area no rocks of this age have yet been identified. The land thus seems to have been undergoing erosion during late Neogene, ending in the formation of a. remarkable peneplane.
