The topographic features of the Suruga Trough can be divided into five deep sea basins, four gorges and a fan-frontal slope. In a longitudinal topographic section of the trough floor shows a step-like topography with prominent three steps. The lower, middle and upper steps correspond to the southern, middle and northern parts of the Suruga Trough, respectively. In the southern part (water depth is 2900-3700m), the characteristics of a convergent boundary are essentially similar to those in the Nankai Trough. The subducting Philippine Sea Plate (PHS) is at least broken to three slabs by the ENE-WSW reverse faults with dextral strike-slip motion. The slabs dip 6° to 10° west. The trough floor gently dips landward, and the main channel shows a reversed sigmoidal meandering pattern. The trough-fill sedimentary sequence is characterized by wedge-type shape and seaward thinning-out trend. In the middle (1750-2900m) and the northern (0-1750m) parts, the accretionary prisms are in direct contact with the subducting plate (PHS), and PHS dips 23° or more west. The trough-fill sedimentary sequence don't show a wedge-type shape, but it is like a slope-basin sequence which filled up a depression on the accretionary prism. This sequence is more intensely deformed in the northern part than the middle part. The main channel shows the sigmoidal migration pattern. In these parts, the trough floor dips east or south-east as clearly shown in a cross section of the trough. These structural features of the Suruga Trough has been formed by the collision of the Tanzawa block at the late Miocene and of the Izu block at the middle Pleistocene to the Honshu Island. At the late Miocene, the bending of the paleo-Nankai-Suruga Trough also formed, and this time corresponds with the time that the plate motion of the PHS changed north to northeast.
The Matsuzaki Lowland is a valley bottom plain situated in the lower reach of the Naka River which flows from the southern part of the central Izu Peninsula. To clarify the sedimentary environment and its change during the Holocene in the Matsuzaki Lowland, all core boring was carried out to take systematic samples. The environmental changes of the Matsuzaki Lowland region was reconstructed on the basis of the observation of the sediments, C-14 dates, analysis of volcanic ash and palaeontological analyses of molluscs, foraminifers, ostracods and diatoms from the cored samples. The environmental changes and palaeogeographical evolution during the Holocene in the Matsuzaki Lowland are summarized in the following. 1. ca. 10, 000-9, 000 years ago At this stage, the sea level was remarkably lower than the present and the sea had not yet invaded into the present Matsuzaki Lowland and the fluvial deposits were accumulated in the lower reach of the Naka River. 2. ca. 9, 000-8, 000 years ago Judging from the appearance of the shallow marine mollusca such as Grassostrea gigas and Batillaria zonalis, a tidal flat was formed in the lowland by the Holocene transgression. 3. Ca. 8, 000-7, 000 years ago As the sea level rose, the sea water invaded into the inner part of the present Matsuzaki Lowland to form a drowned valley. In the outer part of the drowned valley, Teora lata, Ringicula doliaris and Putilla matusimana etc. wihch live in the subtidal environment dominated in the molluscan assemblages, and the benthic foraminifera such as Elphidium advenum and Pseudononion japonicum which live on the sandy bottom in the middle to the outer part of a bay were more common than Ammonia beccarii. On the other hand, the shallow marine mollusca and Ammonia beccarii were abundant in the inner part of the drowned valley. Judging from these results, the outer part of the drowned valley became deeper than the former period. 4. ca. 7, 000-6, 000 years ago According to the abundance of the subtidal mollusca both in the outer and the inner parts of the drowned valley, a whole area of the drowned valley was under a subtidal environment. In this period, the ratio of the planktonic foraminifera increased and the subtropical benthic foraminifera such as Bulimina cf. fisiensis and Trimosina orientalis appeared even in this drowned valley. This indicates that the influence of the open sea water became stronger than before. 5. ca. 6, 000-5, 000 years ago The inner part of the drowned valley began to be filled with the fluvial deposits. In the outer part of the drowned valley, the mollusca such as Nitidotellina minuta and Semelangulus tokubeii which live on the sandy bottom appeared. At this stage, a sand bank began to be formed by the accumulation of sand and gravel on the sea floor of the bay mouth. 6. ca. 5, 000-3, 000 years ago Judging from the appearance of the shallow marine mollusca such as Crassostrea gigas and Batillaria zonalis, the inner part of the drowned valley changed into a tidal flat again. The ratio of the planktonic foraminifera rapidly decreased and Ammonia beccarii forma A which lives under the low salinity condition increased in the inner part of the drowned valley. These represent that the influence of the open sea water was reduced. On the other hand, the development of a sand bank continued in the outer part of the drowned valley. 7. ca. 3, 000 years ago The inner part of the drowned valley was changed into a swampy area by the construction of the sand bank on the bay mouth. The upper limit of the marine deposits in the Matsuzaki Lowland is identified at 5m below the present sea level by the fossil analysis. Its age is estimated at about 4, 000 years ago. This indicates that the western coast of the Izu Peninsula has been subsiding during the late Holocene.
This paper describes the chemical characteristics of monthly precipitation in Iceland. Monthly precipitation had been collected at Rjupnahaed from January 1958 till December 1979, and had been collected at Vegatunga from September 1960 till April 1973. Since 1980, monthly precipitation has been collected at Irafoss. In this paper, we discuss the chemistry of monthly precipitation at Rjupnahaed and Vegatunga. Monthly precipitation was collected by using an open sampler. The open sampler collects bulk precipitation contaning the wet and dry deposition of chemical constituents. Bulk precipitation displays the combined effects of all water soluble airborne components of precipitation. The data of chemical composition of monthly precipitation has several errors. These are mainly due to the procedures of collection and analysis of precipitation. The errors of using data are eliminated by the three steps. The time series of the amount of monthly precipitation, pH and monthly chemical depositions at Rjupnahaed are shown in Fig. 4. Before the middle 1960's, pH of the monthly precipitation had decreased gradually. The coal for house heating has not been consumed since the middle 1960's in Iceland, and the consumption of clean energy (geothermal and electrical) has been increasing. The change of the energy form is considered to be the reason for the variation of pH of the monthly precipitation, . As may be seen from Fig. 4, the monthly depositions have the seasonal variation. The amount of chemical deposition in winter is more than that in summer. The evident tendency of the long-range fluctuation of the amount of monthly chemical deposition has not been observed. The monthly depositions of sodium, potassium and magnesium show the same variation as that of chlorine. We will discuss the chemical characteristics of monthly precipitation by using the mean data for each month, since the monthly chemical depositions clearly have the annual variation, as described before. The sources of the chemical constituents are discussed by using the data of mean monthly depositions (Fig. 5). The predominant source of chlorine, sodium, potassium and magnesium is considered to be sea water. On the other hand, a part of sulfur in the precipitation comes from sea water, and anthropogenic emission in North America is considered to play an important role. Calcium depositions vary with location to a great degree. This result suggests that the source of the excess calcium exists in Iceland. The mean monthly deposition of sea salt in Iceland is larger in winter than in sum-mer. However, the mean monthly depositions of excess sulfur and excess calcium do not indicate the annual variation. In winter, the mean wind speed at 850mb is higher and the pressure at the surface is lower. This evidence suggests that the activity of air convection is stronger in winter. The activity of air convection is considered to govern the annual variation of the deposition of sea salt.
VI. Geological researches in the Festoon Islands in the Northwestern Pacific Side ;The geology of Hokkaido began with PUMPELLY's route survey in the Oshima peninsula in 1862, succeeded by LYMAN, 1976 and others and strongly promoted since 1930 when the Geological Institute was founded in the University of Hokkaido at Sapporo. The geological survey in South Sakhalin was done by Japanese geologists from 1905 to 1945. In Taiwan there were some pioneer works from 1849, but the geological survey was not undertaken until 1895. A preliminary geological map of Taiwan was first published in 1897. Subsequently Taiwan and the Ryukyu Islands were investigated by many geologists. The geology of Taiwan was well developed by Chinese geologists since 1946. J. MILNE and E.. NAUMANN's observation on the volcanic eruption of Oshima, 1876 was the first article in the geology of Izu Islands. Later the grand Ogasawara-Mariana arc and also the Marshall and Caroline Islands were surveyed by TAYAMA and others. VII. In Indochina the history of research goes back to 1874. The geological survey became very active since the institution of its organization at Hanoi, 1898. The existing knowledge was once schematized by FROMAGET in 1941. The western civilization has influenced upon the Philippines much earlier. Present knowledge there, however, mostly a product in this century and its advancement was much accelerated in recent years. In Netherland East Indies the geological survey was started in 1850. Its advancement of a century was compiled by VAN BEMMELEN in his Geology of Indonesia, 1949. In British Borneo or East Malaysia the research history is shorter. In the Malayan peninsula and Singapore, on the contrary, the oldest record may be HAMILTON's navigation, 1688-1723. The geological research there was, however, very slow. SCRIVENOR's Geology of Malaya appeared in 1931. Its comparison with Geology and Palaeontology of Southeast Asia vol. 25, 1984 shows that the change between these two books in a few decades is really astonishing. Little was known of the geology of Siam or Thailand before 1890. Its outline was figured out by the geological survey in 1949 and the knowledge raised up to the same level with those of Malaysia and Indochina in last three decades. VIII. China, Korea and Japan constitute an area of Pentsao where exists a prolonged history of study on the earth and stones. The modern geology propagated into Eastern Asia from last century. As the result it is known there that the Oriental Heterogen was intercaled between the Mongolian geosyncline in the north and the Tethyan geosyncline in the south and the latter extended easterly into the Chichibu geosyncline which was in turn confluenet with the Mongolian geosyncline during the Palaeozoic era. Finally, brief notes are added on the arcuate mountain systems on the western Pacific side (3), Opposition in the geological history between the northern Atlantic and western Pacific sides (4), international cooperation (5) and romanization of technical terms in the countries using Chinses characters (6).