extinct volcanoes, Professor J. Milne has pointed out that it is
literally true of the Kuriles alone, partially true for the northern
half of the Main Island and for Kiūshiū, and quite incorrect as
applied to the southern half of the Main Island and to Shikoku.
This authority sums up the geology of Japan briefly and succinctly
as follows (in Things Japanese, by Professor Chamberlain): “The
backbone of the country consists of primitive gneiss and schists.
Amongst the latter, in Shikoku, there is an extremely interesting
rock consisting largely of piedmontite. Overlying these amongst
the Palaeozoic rocks, we meet in many parts of Japan with slates
and other rocks possibly of Cambrian or Silurian age. Trilobites
have been discovered in Rikuzen. Carboniferous rocks are represented
by mountain masses of Fusulina and other limestones. There
is also amongst the Palaeozoic group an interesting series of red
slates containing Radiolaria. Mesozoic rocks are represented by
slates containing Ammonites and Monotis, evidently of Triassic age,
rocks containing Ammonites Bucklandi of Liassic age, a series of
beds rich in plants of Jurassic age, and beds of Cretaceous age
containing Trigonia and many other fossils. The Cainozoic or
Tertiary system forms a fringe round the coasts of many portions
of the empire. It chiefly consists of stratified volcanic tuffs rich in
coal, lignite, fossilized plants and an invertebrate fauna. Diatomaceous
earth exists at several places in Yezo. In the alluvium which
covers all, the remains have been discovered of several species of
elephant, which, according to Dr Edmund Naumann, are of Indian
origin. The most common eruptive rock is andesite. Such rocks
as basalt, diorite and trachyte are comparatively rare. Quartz
porphyry, quartzless porphyry, and granite are largely developed.”
Drs von Richthofen and Rein discuss the subject in greater detail.
They have pointed out that in the mountain system of Japan there
are three main lines. One runs from S.W. to N.E.; another from
S.S.W. to N.N.E., and the third is meridional. These they call
respectively the “southern schist range,” the “northern schist
range,” and the “snow range,” the last consisting mainly of old
crystalline massive rocks. The rocks predominating in Japan fall
also into three groups. They are, first, plutonic rocks, especially
granite; secondly, volcanic rocks, chiefly trachyte and dolerite;
and thirdly, palaeozoic schists. On the other hand, limestone and
sandstone, especially of the Mesozoic strata, are strikingly deficient.
The strike of the old crystalline rocks follows, in general, the main
direction of the islands (S.W. to N.E.). They are often overlain
by schists and quartzites, or broken through by volcanic masses.
“The basis of the islands consist of granite, syenite, diorite, diabase
and related kinds of rock, porphyry appearing comparatively
seldom. Now the granite, continuing for long distances, forms the
prevailing rock; then, again, it forms the foundation for thick strata
of schist and sandstone, itself only appearing in valleys of erosion
and river boulders, in rocky projections on the coasts or in the
ridges of the mountains. . . . In the composition of many mountains
in Hondo (the main island) granite plays a prominent part. . . .
It appears to form the central mass which crops up in hundreds of
places towards the coast and in the interior. Old schists, free from
fossils and rich in quartz, overlie it in parallel chains through the
whole length of the peninsula, especially in the central and highest
ridges, and bear the ores of Chū-goku (the central provinces),
principally copper pyrites and magnetic pyrites. These schist
ridges rich in quartz show, to a depth of 20 metres, considerable
disintegration. The resulting pebble and quartz-sand is very unproductive,
and supports chiefly a poor underwood and crippled
pines with widely spreading roots which seek their nourishment afar.
In the province of Settsu granite everywhere predominates, which
may be observed also in the railway cuttings between Hiōgo and
Osaka, as well as in the temples and walls of these towns. The
waterfalls near Kobe descend over granite walls and the mikageishi
(stone of Mikage), famous throughout Japan, is granite from
Settsu. . . . In the hill country on the borders of Ise, Owari,
Mikawa and Tōtōmi, on the one side, and Omi, Mino and Shinano,
on the other, granite frequently forms dark grey and much disintegrated
rock-projections above schist and diluvial quartz pebbles.
The feldspar of a splendid pegmatite and its products of disintegration
on the borders of Owari, Mino and Mikawa form the raw material
of the very extensive ceramic industry of this district, with its
chief place, Seto. Of granite are chiefly formed the meridional
mountains of Shinano. Granite, diorite and other plutonic rocks hem
in the winding upper valleys of the Kiso-gawa, the Saigawa (Shinano
river) and many other rivers of this province, their clear water
running over granite. Also in the hills bordering on the plain of
Kwanto these old crystalline rocks are widely spread. Farther
northwards they give way again, as in the south, to schists and eruptive
rocks. Yet even here granite may be traced in many places.
Of course it is not always a pure granite; even hablit and granite-porphyry
are found here and there. Thus, for instance, near Nikkō
in the upper valley of the Daiya-gawa, and in several other places
in the neighbouring mountains, a granite-porphyry appears with
large, pale, flesh-coloured crystals of orthoclase, dull triclinic felspar,
quartz and hornblende.” “From the mine of Ichinokawa in
Shikoku come the wonderful crystals of antimonite, which form
such conspicuous objects in the mineralogical cabinets of Europe.”
(Rein’s Japan and Milne in Things Japanese.) The above conditions
suggest the presence of tertiary formations, yet only the
younger groups of that formation appear to be developed. Nor is
there any sign of moraines, glacier-scorings or other traces of the
ice-age.
The oldest beds which have yielded fossils in any abundance belong to the Carboniferous System. The Trias proper is represented by truly marine deposits, while the Rhaetic beds contain plant remains. The Jurassic and Cretaceous beds are also in part marine and in part terrestrial. During the whole of the Mesozoic era Japan appears to have lain on or near the margin of the Asiatic continent, and the marine deposits are confined for the most part to the eastern side of the islands.
The igneous rocks occur at several geological horizons, but the great volcanic eruptions did not begin until the Tertiary period. The existing volcanoes belong to four separate arcs or chains. On the south is the arc of the Luchu islands, which penetrates into Kiū Shiū. In the centre there is the arc of the Izu-no-Shichito islands, which is continued into Hondo along the Fossa Magna. In North Hondo the great Bandai arc forms the axis of the island and stretches into Yezo (Hokkaidō). Finally in the east of Yezo rise the most westerly volcanoes of the Kurile chain. The lavas and ashes ejected by these volcanoes consist of liparite, dacite, andesite and basalt.
Structurally Japan is divided into two regions by a depression (the “Fossa Magna” of Naumann) which stretches across the island of Hondo from Shimoda to Nagano. The depression is marked by a line of volcanoes, including Fuji, and is in part buried beneath the products of their eruptions. It is supposed to be due to a great fault along its western margin. South and west of the Fossa Magna the beds are thrown into folds which run approximately parallel to the general direction of the coast, and two zones may be recognized—an outer, consisting of Palaeozoic and Mesozoic beds, and an inner, consisting of Archaean and Palaeozoic rocks, with granitic intrusions. Nearly along the boundary between the two zones lie the inland seas of south Japan. Towards the Fossa Magna the folds bend northwards.
North and east of the Fossa Magna the structure is concealed, to a very large extent, by the outpourings of the volcanoes which form so marked a feature in the northern part of Hondo. But the foundation on which the volcanoes rest is exposed along the east coast of Hondo (in the Kwanto, Abukuma and Kitakami hills), and also in the island of Yezo. This foundation consists of Archean, Palaeozoic and Mesozoic beds folded together, the direction of the folds being N. by W. to S. by E., that is to say, slightly oblique to the general direction of this part of the island. Towards the Fossa Magna the folds bend sharply round until they are nearly parallel to the Fossa itself. (P. La.)
It has been abundantly demonstrated by careful observations that the east coasts of Japan are slowly rising. This phenomenon was first noticed in the case of the plain on which stands the capital, Tōkyō. Maps of sufficiently trustworthy accuracy show that in the 11th century Secular Movement. Tōkyō Bay penetrated much more deeply in a northern direction than it does now; the point where the city’s main river (Sumida or Arakawa) enters the sea was considerably to the north of its present position, and low-lying districts, to-day thickly populated, were under water. Edmund Naumann was the discoverer of these facts, and his attention was first drawn to them by learning that an edible sea-weed, which flourishes only in salt water, is called Asakusa-nori, from the place (Asakusa) of its original provenance, which now lies some 3 m. inland. Similar phenomena were found in Sakhalin by Schmidt and on the north-east coast of the main island by Rein, and there can be little doubt that they exist at other places also. Naumann has concluded that “formerly Tōkyō Bay stretched further over the whole level country of Shimosa and Hitachi and northwards as far as the plain of Kwantō extends;” that “the mountain country of Kasusa-Awa emerged from it an island, and that a current ran in a north-westerly direction between this island and the northern mountain margin of the present plain toward the north-east into the open ocean.”
Mineral Springs.—The presence of so many active volcanoes is partially compensated by a wealth of mineral springs. Since many of these thermal springs possess great medicinal value, Japan may become one of the world’s favourite health-resorts. There are more than a hundred spas, some hot, some cold, which, being easily accessible and highly efficacious, are largely visited by the Japanese. The most noteworthy are as follows:—
| Name of Spa. | Prefecture. | Quality. | Temp., F°. |
| Arima | Hiogo | Salt | 100 |
| Asama | Nagano | Pure | 111—127 |
| Asamushi | Aomori | Salt | 134—168 |
| Atami | Shizuoka | Salt | 131—226 |
| Beppu | Oita | Carbonic Acid | 109—132 |
| Bessho | Nagano | Pure or Sulphurous | 108—113 |
| Dogo | Ehime | Pure | 70—110 |
| Hakone | Kanagawa | Pure, Salt or Sulphurous | 98—168 |
| Higashi-yama | Fukushima | Pure or Salt | 117—144 |
| Ikao | Gumma | Salt | 111—127 |
| Isobe | Gumma | Salt | Cold |
| Kusatsu | Gumma | Sulphurous | 127—148 |
