In the Abeshinai district which consists of the Cretaceous formation, it is doubtful if a workable oil deposit can be found, though oil seepages are found at many places. The paper deals with the result of the experiments on the contents of organic matters, extracted by chloroform, and of the quantitative analysis of organic carbon in the mudstones from the district.
1. Tn the mudstones, clastic quartz, plagioclase, a small quantity of biotite, diatom, etc. are observed, but the carbonaceous matters are rare. The matrix consists of clay, fine-grained quartz etc., and is nearly colourless. As secondary minerals, iron sulphide and glauconite are ometimes observed.
2. Quantity of organic matter extracted by chlorcform is 0.026%, on the average. When it is compared with that of the Tertiary source rocks of workable oil fields in Japan, the former is only. 4 ?? 5% of the latter.
3. The result of the quantitative analysis of organic carbon is 0.54% on the average and is 50 ?? 6)% of that of source rocks in the workable Tertiary oil field.
4. Quantities of organic matter, determined by chloroform extraction, and of organic carbon are maximum in the mudstone of the Onodera sandstone formation and are minimum in the mudstones of the Sakotandake sandstone formation.
5. It may be assumed from these results that the mudstones in the Abeshinsi district are not favorable for the source rocks of petroleum.