Uranium in natural waters can be fixed either by precipitation of uranium minerals or by adsorption on some adsorbents such as clay minerals and carbonaceous materials. The precipitation is controlled by factors contributing to the conditions of a system from which a uranium mineral is precipitated, such as temperature, pressure, pH, Eh. and concentration of the elements constituting it. Each factor was examined thermochemically along with some experiments. Decrease in Eh is most effective for the formation of primary uranium minerals, while pH and concentration of such anions as phosphorus, vanadium and arsenic play the most important role in the precipitation of secondary uranium minerals. Adsorption and desorption experiments of hexavalent uranium to montmorillonite, kaolin, and limonite reveal that they have more or less an order of 10, 000ml/g of enrichment factor (Kd) at about pH6. The adsorbed uranium was found to alter to a uranium mineral most favourable for the surrounding condition when aged experimentally. It suggests that the adsorbents perform a kind of catalytic action for the formation of uranium minerals from very dilute solution such as surface waters.

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In 1960, H. URATA and the writer reported on the Paleogene formation in the vicinity of Hokonoko, Kumamoto Prefecture and discussed the possibility of finding a new coal field under the ground of this district.
Meanwhile, it has become known that on the mountain-side in the northern part of Kamoto Machi, a conglomerate formation is distributed narrowly but continuously. The writer names this conglomerate the Fudogan formation, and correlates it with the Akasaki group, because of the close similarity in rock facies, being non-marine, non-fossiliferous, and purple in colour.
The Fudogan formation, about 120m thick, dips southward, and in the plain to the south it goes under the Aso volcanic products but still bears the characters of a basal conglomerate.
During October 1964, seismic prospecting by refractive method was carried out in the plain to the south of the hill composed of the Fudogan formation. The measure line was extended 4.8 km in a NNE direction.
In the above prospecting the following three layers were discriminated:
Seismic wave velocity (m/sec) Thickness (m)
1st layer 1, 645-1, 700 150-300
2nd layer 3, 620-3, 800 400-650
3rd layer 5, 670
Comparing these data with those of the geological and seismic investigations previously obtained, it may be safely said that the 1st layer corresponds to the Quaternary formation and the 3rd layer to metamorphic rocks or granite. After careful examination, the writer comes to a conclusion that the 2nd layer is probably Palaeogene formation ranging from the Amakusa stage to the Ariake or Nogata stage.
If this presumption is correct, the paleo-Ariake Basin proposed by H. MATSUSHITA might have been branched off, extending to this area.
The writer here presumes a possible stretch of a new coal field underlying the Quarternary deposits in this area.

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It has been previously discussed among some geologists that the Kishima group was deposited on the pre-Kishima erosional surface of the underlying Ouchi group. The discussion has been based mainly on the remarkably varying thickness of the uppermost part of the Yoshinotani formation which occupies. the upper part of the Ouchi group.
According to the writer's observation of the boundary between the two groups, however, the vertical changes in lithofacies from the Yoshinotani formation to the Kishima formation are very gradual and any evidence to imply unconformable relation is not found at most of the outcrops in the coal field.
In order to re-examine the thickness variation of the strata, the writer drew isopach maps based on some marker horizons as illustrated in figure 2, for the Yoshinotani formation and the lower units of the Kishima group, such as the Kishima formation, the Sari Sandstone and the Honeishi Zone. Comparison of the patterns of the isopach maps reveals that the pattern of the isopach map of the uppermost. Yoshinotani formation (figure 3) is very similar to those of the units of the Yoshinotani formation and the Kishima formation (figures 4 and 5), but is different from those of the Sari Sandstone and the Honeishi Zone (figures 6 and 7).
The result of the pattern comparison suggests that the remarkably variable thickness of the uppermost Yoshinotani formation is attributable to local variations in subsidence of the depositional basin than to erosion of the pre-Kishima age, and that the late Oligocene Ashiya marine transgression may have extended mainly over this area during the deposition of the Sari Sandstone.

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