In Japan, soil erosion on hillsides is wel-l-demonstrated in the Okayama District along the Setouchi Coast. After a study of this district, the following conclusion were reached
1. Bare hillsides are found mainly along the ridges and adrept slopes of granitic hills. Other hills, of Liparite, Chichibu system, or Tertiary rocks, are not as bare as the granites. As a result of experiment, it was found that as much as 20 or 30 tons of soil are eroded, even on the surface of the Chichibu Palaeozoic rocks, when vegetation is lacking.
2. From macroscopic observation, it may be said that the bare lands are not generally found in mountains or thinly populated regions but, rather, in regions of dense population and thriving economic activity similar in topography and geology. This indicates the cause of erosion to be man's destruction of vegetation and soils.
3. Many of the bare hills surrounding the Okayama Plain have been abandoned and eroded. since the beginning of the Mei ji Era (1869-1912), a period of general disorder in forestry. Following this came the so-called “forest eater” stage of destructive erploitation of forest resources; streams and brooks built up their beds for 50 to 60 years, raising them to 5 or 10 meters above the adjacent fields. These rivers are termed “Tenjo-gawa” or “Flying rivers.”
4. Records and documents concerning the forests and plains in this region date back to pre-Meiji days. Archives indicate the three centuries prior to 1896. may be divided into three distinct periods:
A-The third period: At the beginning of the 18th century, bare hills appear mainly on the Kojinma Peninsula distributed approximately as they are now (Figure 1.), differing only in detail, For example, the center of distribution was in the center of the peninsula instead of near Tainano as at present.
B-The second period: For the second, half of the 17th century there are no clear records of bare land in the archives. In this period it seems likely that the hills were covered by pine forests even more thickly than previously.
C-The first period: For this period documents are scarce, but it is clear thet a vast plain was utilized for grazing of cattle with a portion of it eroded.
In summary, it appears that there were two periods of accelerating soil erosion separated by an era of comriparative stability (Table 1).

抄録全体を表示

In the eastern part of Hokaido, in one of Japan's most famous national parks is Lake Akan, situated in the Akan Caldera. The Akan Caldera is surrounded by Mounts O-Akan (1371m), Me-Akan (1503m.), Furebetsu (1097m), and Fuppeshi (1225m), All of which are believed to have been formed following subsidence of the volcono and formation of the Caldera.
During the summer of 1951, the writer was engaged in a survey of lake deposits and lacustrine terraces. Wide areas of lacu.strine terraces were found around the lake and the following conclusions were reached:
(1) Lake Akan is presumed to be a dammed lake from the fact that Tanakadate had discovered the clear shape of drowned valleys on the bottom of the lake. The writer believes that the upper stream of the Akan River flows down within the district of volcanic lava-flow.
(2) The height of lacustrine terracers is approximately 440 meters above sea level while the present lake level is 419 meters. Hence. the height of the lacustrine terraces indicate the level of the palaeo-lake and it nay be presumed that the lake once extended to the upper part of the Akan River. Supporting this idea is the writer's finding of diatomn fossils, such as Melosira italica, and Stephanodiscus astraea, both of which are characteristic of lakes. The inferred height of the palaeo-lake level has coincided with that obtained from the table work at summit level.
(3) Drs. Minato and Ishikawa consider that the form of the Akan caldera was caused by a volcanic mud-flow in the late Diluvium, as in the case of Lakes Towada, Shikotsu, Hakkoda and Kutcharo, The writer regards the thickness of the volcanic mud-flow as not very thick from observations of mudstone having N24°E, N8° in that dip and a strike near the lake shore. It appears to be a case indicated by Dr. Kuno and other geologists who consider bed rock . under volcanoes to be found frequently in high positions of the volcano.

抄録全体を表示

(1) Seasonal change in the amount of deposition and the chemical nature of the deposits have been investigated in Nakanuma, a swamp it Ibaragi Prefecture.
(2) Seven glass bottles were suspended from a buoy at the depth of 1-10m above the deepest bottom of the lake. At intervals of about one month, they were hauled up, and their contents examined.
(3) The rate of deposition was largest between March. 11 and April 29 (14.8g/m²/24hours), and it was smallest between July 11 and August 25 (7.8g/m²/24hours).
(4) The percentage of total nitrogen was found to vary between the two extreme value of 0.62% (Mar. 11-Apr. 29) and 1.05% (Jun 24-July 17). The content of organic carbon varied between 4.7 (Mar. 11-Apr. 29) and 6.6% (Aug. 25-Sept. 24). While, the surface layer of the bottom deposits, which was dredged from the deepest part of the swamp, contained 0.38% of total nitrogen and 3.3% of organic carbon.
(5) The deposits, formed during the summer stagnating period, contained large amount of organic detritus, which were produced as the result of biological production in the lake. On the other hand, the deposits, during the winter and early spring, contained great quantities of inorganic remains which were brought from the shore or bottom of the swamp by the wind action or water circulation.
(6) The value of the ratio N/C was larger during the spring and summer (0.13-0.19), and smaller during the autumn and winter (0.11-0.12). While, the bottom deposits showed 0.11 as N/G ratio.
.The abnormal value of N/C ratio during June and July (0.19) was explained as the result of the appearence of large amount of blue algae (N/C, 0.17-0.19) in this period.
(7) As compared with other lakes, it seemed possible to suppose the correlation between to suppose the corre-lation between the quantity of the deposition and the dean depth of lakes.

抄録全体を表示

It is believed that expansion of truck gardening areas is related to that of the urban district. Two indicators concerning truck gardening areas were used: one is the supply of human manure (used as fertilizer) from the urban district; the other is the supply of fresh vegetables provided theurban district by the villages. Documents show that the former practice developed in the middle of the 18th century at the same time as the development of the latter (Figure 1 and Table 1). The villages which supplied Edo with fresh vegetables are shown in Figure 2.
On the other hand, according to Yosuke 'Watanabe, in the middle 17th century the outline of the urban area of Edo was almost the same as that of Tokyo in the 1930's. Therefore, it may be deduced that a broad truck gardening area had already developed by the middle of the 18th century as shown in Figure 1.
In the case of Nichome (Shiodome-mura of Minamisaitama-gun in Saitama Prefecture), farmers purchased the human manure which was carried to them by river craft along the rivers and canals in and around Edo as shown in Table 1. In connection with dealing, in human manure, there were occasional quarrels over conflicting spheres of interest.
These two indicators have not yetbeen surveyed as they apply to, the western part of Edo in the same period, but it appears that the gardening area of eastern Edo was greater than that of the western part chiefly because the former has many more rivers forming networks which could be utilized as transportation media.

抄録全体を表示

The Daimyojinzawa flows frozen the water shed of Mounts, Neko and Azuma and run southward to join the Tikuma River at the city of Ueda. It is a short stream only 5 Kilometers in length and its waters contain, a poisonous acid. The acid. contents originate from a sulphery mine located at the source of the river. The writer examined the tem-nperat;i.re of the water, its hydrogen ion concentration, and the its amount of discharge at several stations. (Fig. 1, Tab. 1) Analyses of some ingredients were made at 5 Points by taking water samples (Tab. 2). As a result of these observations, the following conclusions were reached:
(1) The acid cotent of the water is increasing due to prospectingat at the sulphur mine.
(2) Although. it is believed that the acid content increases during low water season and decreases, at high water season, it also increases at some high water periodes such as the snow-melting season.
(3) The acid content will increase further when mining is resumed

抄録全体を表示