In this paper, the writer summarized some petro-geological investigation of basaltic rocks that seems to have been overlooked by most petrologists. Though the general tectonic sequence and magmatic cycle in the diastrophism is not yet fully realized, we find some intimate association of certain types of tectonism or tectonic stages and certain types of magmatism represented by some characteristic types of basaltic rocks. For these phenomena the writer presents some tentative interpretation, based on many geological facts and petrological data from various basaltic fields in our country and over-seas, in view of the general theory of tectonism compatible with the recent geophysical knowledge concerning to the crust and depths of the earth. In connection with these magma-tectonic investigations, the writer made some inquiries on the varieties and composition of basaltic rocks erupted in older and newer geological periods. For the general tendency that distinctly femic or salic types of basalts and alkaline basaltic rocks are more abundant in newer than older geological periods, and that the range of composition extends, generally, as geological age becomes younger, the writer is of opinion that it is attributable mainly to the effect of denudation subsequent to the eruption of basaltic rocks characteristic in areas of positive tectonism, by which a greater part of them is removed, instead of being preserved within the sedimentary formation as in the case of basaltic rocks in negative tectonic areas that are relatively simple in their types and compositions.
This paper undertakes to analyse the recent migration status of urban places in Japan with reference to their functional status, using the data obtained from the censuses of 1950 and 1955. The total net-migration is estimated for all cities and the net-migration by sex and age is estimated for the cities of population of over 200, 000. In the period between 1950 and 1955, about two-thirds of cities had lost population by migration. The poulation lost by those 330 cities counted to 730 thousand, and on the contrary, the population gained in the rest of the cities counted to 3.2 million. The heavier concentration of population is observed in the bigger cities, that is, the six big cities of Japan occupy more than 80 percent of the total excess of migration of all cities. Out of this, Tokyo has 1.2 million, Osaka 0.4 million. For other cities, industrial and the satellite cities have a big net-migration compared with the size of population. Cities which have a function of commercial or local administrative center are, in general, pull a small amount of population by migration. Those which lost population are ovserved in the cities of newly born by the amalgamation of the towns and villages. The demographic differentials of migrants are also characterized by the fuction of cities. Especially age differentiation is clearly distinguished by the functions. The big industrial cities gained a population aged at 20-24 by a high migration rate, and local center gained a popoulation aged at 15-19. Metropolitan cities gained the population aged at 15-19 as well as 20-24. Thus, the amount of in-migration and the demographic differentials are well expressed by the functional differentials of the cities.
In the second part of this paper, geology and geomorphology of the strait are described. Geologic map and profiles presented here (Fig. 16) are prepared by examining rock specimens dredged from more than two thousand localities in the strait and also by interpreting figures obtained by sonic survey. § 2. Stratigraphy : Exposed formations on the strait seafloor are entirely of younger Tertiary deposits from Miocene to Pliocene in age and associated volcanic rocks such as basalt, andesite and rhyolite. They are underlain by so-called Paleozoic rocks that crop out around Cape Shirakami of Hokkaido and overlain by submerged Pleistocene formations and Holocene sediments. Tertiary formations of this area are as follows in ascending order. Fukuyama formation (Fy) : Mostly tuff, agglomeratic tuff and welded tuff and conglomerate at the base 330 meters in the thickest. Kunnui formation (Kn) : Unconformable to the underlying formations. Thick or thin alternation of tuff (so-called green tuff in the main), tuffaceous sandstone and mudstone with occasional intercalation of agglomerate, conglomerate. It may be divided into several members (Kn1-Kn5) by lithic assemblage, although lithofacies and thikness are both variable at places, and volcanic members predominate in the southern half. Foraminifer fossils show its age to be middle Miocene. About 1, 300 meters in total thickness. Yakumo formation (Yk) : Unconformable to the former formation. Plately bedded so-called hard shale with interbedded tuff. Pyroclastic member thiken in the south. Radioralia and diatom fossils are very common. More than 400 meters in the thickest. Kuromatsunai formation (Km) : Massive, diatomaceous tuffaceous siltstone or sandy mudstone. Frequent intercalation of thin layers of tuff and marl. 800 meters or more in total thickness. Setana formation (St) : Unconformable to the underlying formation. Mostly soft sandstone and partly conglomeratic. Rich in fossils of foraminifers and molluscs of upper Pliocene age. Thickness is more than 115 meters. Volcanic rocks : Intrusion of basaltic rocks and andesitic rocks as well as rhyolite is found at places and particularly extensive in the south. Interbedded volcanics, mostly basic in nature are tracable from place to place, mainly in the south. § 3. Geologic structure : Essential geologic structure of the area is anticlinal, treanding from northwestnorth to southeastsouth and it forms broad saddle structure by lowering down of formations, accompanied by faults, toward the center of the strait from both lands. Consequently, younger formations are distributed on both flanks of anticline and also in the middle of the strait. The opening of the strait is due chiefly to the exposing of these soft, younger formations such as Kuromatsunai and Setana in the middle of the area. Foldings of minor order are also observed within the broad anticline, some of them being brought by faulting. Four fault systems are recognised in relation to geologic structure as well as to time sequence. The first system is longitudinal and is followed by second dextral transversal fault group which lets the formations sink toward the center of the strait and also they shifted the northside of faults toward east. The third system, longitudinal in the south and diagonal in the middle of the area, divided the area into four major units. All these three systems are after the Kuromatsunai formation, while the last longitudinal system is younger than the Setana formation and forms horst topography at the southern half of the strait.