鹿児島縣宇治群島および草垣島の地質
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概要
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The Uji group of islands (Uji gunto) and the Kusagaki group (Kusagaki jima) are two groups of uninhabited islets scattered at a distance of about 70 km and 90 km respectively to the south west of the western point of Noma peninsula, Kagoshima Prefecture.<BR>At the end of May, 1953, the writer paid a short visit for several days to these islets to carry out a scientific survey enterprised by Kagoshima University. They had been left scientifically untouched till the present survey.<BR>The longitudinal axes of these islets run SSW-NNE and many rocks are arranged in the same direction.<BR>A greater number of islets in both the Uji group and the Kusagaki group are composed of these augite-hornblend andesite and co-essential agglomeratic lava which are fairly dissected. The sandstone beds which are intruded by the andesite outcrop only in a very small area on the southern coast of Mukai-jima of the Uji group. Although the exact geological age of the andesite and the sandstone beds is uncertain, they will be, judging from the petrographical and stratigraphical evidences just given, correlated respectively with the hornblend andesite and a member of unknown. Mesozoic formation in the northern districts of Sendai City, Kagoshima Prefecture.<BR>The probable north-east prolongation of the longitudinal axes of the above mentioned islets trend toward Sendai district. Personally, he is inclined to the opinion that these islets are structurally connected with the mainland, and also the northern part of arcuate Riukiu islands is divisible into four longitudinal zones which are, from the inner side, arranged in the following zones Palaeo-Riukiu Volcanic, Meso-Neo-Riukiu Volcanic, Palaeozoic and Granitic, Tertiary.