M. Saito

At the latter locality the thrust plane strikes N 80" W and dips 45' S, and the Izumi group in this vicinity has the same strike and dip The Izumi is disturbed within a distance of five to six meters from the fault plane, forming there a kind of brecciated zone The Kawauchi formation near the fault consists of angular pebbles of sandstone and slate derived from the Izumi group in a matrix of blue silt Laterally this grades into blue silt At about 10 meters north of this outcrop and in a lower horizon the subangular to angular pebbles and cobbles of sandstone derived from the Izumi group make a 20 meters deep gorge.

In the bed of the Doki River at Naiden in Kotonami-mura, the basal part of the Kawauchi for- mation is exposed, the lowest consisting of arkose sand and is thought to be the weathered products of the basement granitic rocks. In this sand are found erect stumps with their roots penetrating the arkose sand, all still in original position (P1 4, Figs. 7-8) A~ound the roots are found thin covering of greenish silt Above this sand there is a 50 centimeters thick green sandy silt with plant fragments and with lenticular carbonaceous matter From the lenticles were found .!etasequoza dzstzcha MIKI, Pseudotsuga japonica SHIRASAWA, and Pzcea Maxzmowzczzz REGEL This is succeed- ed with a one meter thick, gravel deposit consisting of subangular cobbles and boulders of sandstone derived from the Izumi group and of granite from the basement, and cemented with green arkose sand (PI. 4, Fig. 9) Tracing this gravel deposit eastwards along the river bottom, it found to directly cover the basement of granitic rocks near the shrine in Naiden, Kotonami-mura

In the cliff of the road at Inoo in Kotonami-mura is exposed a one meter thick varved structure sandy silt overlain with one to two meters thick pebbly arkose sand and a one to one and a half meters thick muddy silt yielding abundant remains of T r a p a discoidpoda MIKI and 7 tetragona MIKI This is succeeded with a 20 centimeters thick medium grained sand layer in which a dense parallel arrangement of stems and leaves admixed with the sand, and from this layer were deter- mined such fossils as Cunnznghamza Konzshzz HAY., Chamaecyparz s pz s z f e r a ENDL and Metaseguoza dzstzhca MIKI.

Above this plant bearing deposit there comes a four or five meters thick pebbly sand in which is intercalated a 30 centimeters thick silt layer and sedimentar y structures of east-west trend are d e - veloped These sedimentary structures consist of the dragging down of one part and squeezing of the other, and associated with it are stretched slabs of silt and on the sides of the dragged down part of the silt there can be observed injections of the surrounding sand into it. This suffices to indicate the plastic nature of the silt layer, its elasticity and unconsolidated nature a t the time of its for- mation This may also suggest that the conditions of the sedimentary basin may have not been stable This is overlain with unconformity by the Yakeotoge gravels. At the north side cliff of Hazama-ike

in Manno-cho, in the northern part of this province, within a very restricted area there is exposed a one meter thick white tuff, covered with a 20 centimeters thick muddy peat which abuts against the granite From this muddy peat, pollen have been found, these comprise, Metasequoia ( 8 %) ^, Pzcea ( 7 %), T s u g a (1 O % ) , Abzes (4 5%), Pinus (36%), Quercus (14%), Alnus (12%) This may be a relic of the lacustrine deposits

J - 4 . Eastern Province

In the eastern province there are developed 500-600 meters high hills of granite flanking the northern side of the Asan mountains which consist of the Izumi group. The lacustrine deposits occur mostly on the northern side of this granitic hills or as valley filling deposits of the granitic hills and no lacustrine deposits have been found in association with the Izumi group as seen in other province. These will be described in the following lines and it may be stated that the present preservation of the lacustrine deposits in the lower parts of the ~ e l i e f indicates the degree of erosion that had taken place after their deposition. Although plant fragments are found at several places of the lacustrine deposits in the province, no determinable ones have been collected.

The type locality of the Taman formation which is distributed in this eastern province is the road cutting in the low reliefs of the granitic hills between Taman and Kudarikura in Ayagami-mura.

Here the lowest part of the formation is not exposed but below the Taman bridge in Taman, Ayagami-mura, a two meters thick blue sandy silt becoming white upon weathering and intercalating lenticular gravels and some plant fragments is developed, and above it is a two meters thick gravel bed of which gravels are subangular cobbles of hornfels, diorite, granite cemented with arkose sand included into the gravel bed as derived materials from the basal conglomerate of the Izumi group.

Tracing this gravel deposits southwards along the stream bottom they abut against the basement granite and the boundary is obscure.

The Ge0log.y o,f' K a g a w a and Northern Ehime Pre,f'eclu~es

35 The upper part is exposed in the east of this area at Shimowada, Ayagami-mura. Above the gravel deposit described above there is a four meters thick pebble deposit of subrounded gravels of granite and sandstone derived from the Izumi group, overlain with a one meter thick blue sandy silt and a five meters thick arkosic sand This is covered with a five meters thick gravel deposit of subround- ed to subangular medium to large pebbles of sandstone derived from the Izumi group, and also small subrounded pebbles of both slate and granite and these are cemented with arkose sand. This is covered with unconformity by the Yakeotoge gravels.

In the north of this area in the vicinity of Kamisenbiki, Ryonan-cho, there is an alternation of tuffaceous silt and arkosoic sand measuring about 10-15 meters in thickness This facies is also of the lacustrine deposits.

In the eastern part in the vicinity of the Higashiueda Primary School in Yamada-cho, Kida-gun, a four meters thick srkose sand with limonite layers intercalated is exposed (PI 13, Fig. 3 ) .

At Nishiueda in the south of Jinnai-ike covering the granodiorite with unconformity there is ex- posed a 50 centimeters thick tuffaceous silt overlain with a four meters thick arkose sand with intercalated limonite layers, in upward succession.

In the vicinity of Nishihoji, Yamada-cho in Kida-gun there is exposed a 50 centimeters to one and a half meters thick gravel deposit consisting of weathered granite and andesite cobbles lying unconformably upon the 30 centimeters tuffaceous gray silt under which there is a one meter thick arkose sand with weathered grains of feldspar grains Under this, there is exposed a 30 centimeters thick tuffaceous clay. Here the formation strikes N 40' W with 30° SW dip, thus there is an angular unconformity between the lacustrine deposits and the terrace deposits

In the road cliff in Nakashiro in Miki-cho, Kida-gun there is exposed a five meters thick terrace gravel deposit covering a one to one and a half meters thick blackish purple, faintly stratified, brecciated tuff with angular fragments included. This facies is thought to correspond to the Taman for mation.

In the northern part of this province in the vicinity of the summit of Yashima hill, within a very restricted area there is exposed unconformably above the reddish purple agglomerate of the Sanuki group, a two to five meters thick granule sand deposit in which are intercalated small pebbles of subangular to subrounded glassy biotite andesite, biotite granite and rarely also of mica- schist, and the cement of decomposed coarse arkosic sand. Stratification is developed a t about five centimeters intervals and the granule and sand zones alternate. The biotite flakes are parallel with the stratification being almost horizontal This deposit is also considered to belong to the lacustrine deposits (Pl. 5, Figs. 1, 5)

The lacustrine deposits which extend through the four provinces distinguished in this article occur only sporadically either as valley filling deposits of the basement of granitic rocks, along the northern sides of the granitic masses or along the foots of the Izumi group making up the mountain range extending in east-west direction. Also they are frequently covered with younger deposits and therefore their direct tracing in the field i s often difficult. However, from the characteristic lithofacies a s well a s the relation with the older rocks, distinction of the lacustrine deposits is not difficult.

The differences in lithological characteristics according to locality within the four provinces seems to indicate the local environmental conditions of the lake. The good development of gravel facies and of arkose sands is a typical feature of the deposits and readily indicates the rapid deposition in those areas and also that weathering must have been progressive there. The rapid deposition of such deposits can be noticed from the orientation of the gravels and sands making the deposits a s well a s from the strong relief of the basement over which the lacustrine sediments were deposited.

As will be lepeated in another section of this article i t is evident that the lacustrine

deposits originally had an extensive distribution, but are now only represented a s erosion

relics, being preserved in the depressed areas such a s in the valley of the granite hills

then existing. This may also be indicated from that true deep water lithofacies of lacus-

trine deposition are not found because the greater part of the lake has been removed by

erosion, and only the lower parts of the originally deposited sediments are now preserved

M . Saito

K Yakeotoge Gravels

The Yakeotoge gravels are a name proposed for the gravels distributed a t the heights of about 80-300 meters, the latter at Yakeo-toge (pass) and the former Konan-cho, Kagawa-gun, Kagawa Prefecture These gravels are unconformable with the older deposits such a s the lacustrine deposits, Izumi group and granite, and the younger deposits consist of terrace deposits with which it is unconformable. The gravels of the Yakeotoge are generally subrounded to subangular pebble to cobble size, rarely with boulders, and consist of sandstone and slate of the Izumi group, granite, crystalline schist, quartzite, hornf els and andesite, being derived from the older rocks. The proportions of the kinds of included gravels are related with the kind of rocks making the basement and those of the hinterland, thus they show considerable variation according to places T h e matrix is generally in the range of small pebbles, granule to coarse grained sand However, a t places the matrix may be reddish and loamy a s at Kawakami hill in Kawauchi-cho in Ehime prefecture, the Nukita hill in Mishima City in Ehime Prefecture and the Kudarikura hill in Ayagami-mura in kagawa Prefecture.

And to be mentioned is that the gravels are covered with an about one meter thick white ash layer a t the summits of the Shimowada hills in Ayagami-mura in Kagawa Prefecture, being found from no other locality.

These gravels are distributed in the four distinguished provinces and the thickness varies from 15-60 meters. The Yakeotoge is distributed chiefly in the southern part of the studied four provinces or in the northern parts of the mountain range traversing the island of Shikoku

The type locality of the Yakeotoge gravels is the pass leading from In6 to Nakato in Kotonami- mura, Nakatado-gun in Kagawa prefecture in the Mitoyo-Nakatado province (PI. 5, Fig. 3) Here the Yakeotoge gravels cover the basement granite, Cretaceous Izumi group and lacustrine deposits with marked unconformity (P1 5, Fig 6) At the type locality the gravels measure about 40 meters in thickness and the range is to about 20-50 meters in thickness in the vicinity. The gravels consist in the lower part of a two- five meters thick subrounded small cobbles of granite, sandstone and slate of Izumi group in addition to small pebbles cemented with arkose sand. Above this the 35 meters thick gravels consist of subrounded to subangular cobbles of sandstone and slate derived from the Izumi group sometimes with pebbles of slate and this deposit is cemented with coarse sand to small pebbles The distribution of the Yaketoge gravels is sporadic, but can be observed in the region of four provinces.

In the Aso hills about five kilometers south of Matsuyama City and the Kawakami hills in Kawauchi-cho, Onsen-gun in the Matsuyama province, a t the former locality the 30-50 meters thick Yakeotoge gravels cover the Izumi group with unconformity, and build the 200 meters high hills.

These consist of subangular to subrounded pebble to cobble size sometimes with 50 centimeters in diameter boulders derived from the slate and sandstone of Izumi group, black schist, hornfels, andesite and of quartzite, in a matrix of granule to small pebbles and sometimes of tuffaceous sand In the valley south of Shigemitsu there is a N-S treding fault with vertical angle cutting the Yakeotoge gravels At the locality above mentioned, the Yakeotoge gravels cover the lacustrine deposits and the Izumi group with unconformity. sometimes abutting against the vertically inclined Izumi group (P1 6 , Fig 5). The gravels measure 10-30 meters in thickness, and consist almost wholly of sand- stone derived from the Izumi group, being subangular to subrounded, pebble to cobble size and sometimes with boulders intercalated and sometimes a 30-50 centimeters thick layers of small to medium sized pebbly zone, the matrix consists of coarse grained sand to small pebbles In the upper part of the Yakeotoge gravels the matrix becomes a reddish loam

In the Niihama-Saijo province the Yakeotoge gravels in the 80-150 meters high hill in the south- west of Doi-cho, measure about 10-30 meters in thickness and cover unconformably the Izumi group, and consist of angular schist cobbles and subrounded Izumi cobbles to boulders cemented with loam.

In the Nukita hills in the east of Mishjma City, the Yakeotoge gravels are found at a height of 100 meters, measure about 20 meters in thickness and cover the Izumi group with unconformity. T h e gravels consist of subrounded cobbles of the Izumi sandstone and angular elongated cobbles of black schist cemented with reddish loam. In the immediate east in the vicinity of Kanagawa, the Yakeotoge gravels measure about 20 meters in thickness and cover the Izumi group with unconformity. T h e gravels consist of subrounded pebbles and cobbles of schist, angular cobbles of the Izumi sandstone with a matrix of decomposed schist and micaceous sand

In the Mitoyo- Nakatado province the Yakeotoge gravels in Saida-mura build the 200 meters high

ドキュメント内 The geology of Kagawa and northern Ehime Prefectures, Shikoku, Japan-香川大学学術情報リポジトリ (ページ 38-41)