First of all, testing samples were made by mixing silt and fine sand in various proportions. Then they were saturated with water in glass vessels and it was studied how the component rate of silt and the thickness of the samples affected the cracking which occurred when they were dried. Further, the study was extended to the relations between the rate of silt in the samples and the percentage of water in them in the early stages of cracking. From the test results the following facts were ascertained : 1. Shapes of the cracks which appear in the fine-grained deposit in a given vessel is affected by the component rate of silt. When the rate of silt in the sample is 30 % or more, a relation of some N=As+B (A and B are decided by the thickness of the sample) is observed between the crack density (a tentative name) and the rate of silt. 2. Shapes of the cracks are affected by the thickness of the sample. When the component rate of silt in the sample is 50 % or more, a relation of some N=A-D (A is decided by the rate of silt) is observed between the crack density and the thickness of the sample. 3. The cracking ceases to occur if the rate of silt decreases to some degree. The area where no cracks appear varies with the thickness of each sample, but in any case none of them appear if the rate of silt is less than 10 %. 4. There exists a functional relation of some H=0.006+0.17 between the percentage of water and the component rate of silt in the sample when the first cracking starts. That is, the higher the rate of silt is, the more cracks appear under moisture conditions. In future, the constancy of the above results is to be further confirmed through examinations of such experimental operations as the drying and the mixing of samples and through preparation of more specimens. In addition, the same tests are to be conducted with other kinds clay, their results being applied to general fine-grained deposits.
Since 1967, the Basic Map of the Sea Project has been carried out by the Japanese Hydrographic Department. The results of this survey have been published as the bathymetric chart, submarine structural map, total magnetic intensity chart and gravity anomaly chart of 1/200, 000 in scale. In this paper, the results of survey from 1967 to 1968 were compiled into the bathymetric chart and submarine geological map of 1/500, 000 in scale. In early Miocene Epoch, many sedimentary basins were formed in the environs of the western part of the Northeast Japan and the continental borderland in the sea. In late Miocene, the acoustically transparent sediments deposited in the sea of comparatively uniform sedimentary environment. In early Pliocene, the differentiation of sedimentary basin and the tectonic movement accompanying folding and faulting of NE-SW direction began to take place. In late Pliocene, intense movement of NNE-SSW direction which formed folding and faulted blocks in the Sado Ridge and Mogami Trough, had occurred and the outline of submarine relieves in today were accomplished.
Whereas the concept that the weathered rocks show high porosity and these developed pores in rocks control the compressive strength has been accepted, this paper has attempted to check the effects of different water content and temperature conditions of rocks to compressive strength. In general, in side of pore space, there exist some amount of water as different forms, which mainly depends on temperature. In this study, we chipped rock samples out of weathered tuffaceos sandstone bed rock, and temperature conditions using laboratorical methods. After processed test samples, we measured compressive strength and other properties of each sample. These tests show some interesting results as following short summary sentences; 1) The compressive strength of weathered rock is controlled by the volume and shapes of pores, and materials which occupy the space of pores. 2) If the contained water in pores is frozen, the less amount of water rocks contain, the larger compressive strength value rocks have. 3) If water in pores is frozen, compressive strength of rocks is 3-4 times larger than unfrozen condition. 4) Under the frozen condition, compressive strength value increases in proportion to lowering the temperature below 0°C. It is hoped that the stringency concerning about the strength of weathered rocks in cold regions should be confirmed by the study about pores and materials in pores of rocks in laboratorical works and on-the-spot-investigations.