This part of the article deals with the marine and non-marine Mesozoic stratigraphy, the Mesozoic folded mountains, the Cenozoic history of Thailand and West Malaysia, the summary of the geological history of the region and my retrospect of its research. The marine Triassic formations are distributed on the two sides of the Chiangmai axis in Thailand and of the Malayan main range, the eastern ones of which contain volcanic rocks. In the Malayan peninsula the Triassic and older formations disturbed by orogeny are overlained by the non-marine Tembeling formation. In Thailand the Lampang group on the eastern side was folded in the late Triassic age, while the continuous Triassic and Jurassic formations constitute the Mae Moe group in the Burmese-Thailand border. In East Thailand the Khorat group in the hinter basin of the Pak Lay folded belt consists of upper Triassic-Jurassic paralic sediments and Cretaceous limnic ones. While they are sub-horizontal, the Jurassic and older strata on the Burmese frontier are deformed by the late Mesozoic orogeny and overlain by the Cretaceous red beds. The Tembeling basin in the peninsula was also deformed by this orogeny. At the same time its east side warped down forming the Gagau basin. The older and younger Mesozoic orogenies were associated with granitic intrusions. The Mesozoic folded mountains thus well consolidated were destructed repeatedly by the Cenozoic block movements till at length the present topography was yielded.
Machida and Arai (1976 and 1978) reported two widespread tephras of latest Quaternary age, the Kikai-Akahoya and Aira-Tn ashes, which were produced by gigantic eruptions of the Kikai and Aira calderas respectively in southern Kyushu. These have been used as excellent time-markers in late Quaternary sequences in Japan. In this paper these two tephras are reported in Korea. Accurate determinations of refractive index of the specific volcanic glass contained in the soil are used as the most useful criteria for quick characterization of these tephras, together with stratigraphic nature. As a result, the Kikai-Akahoya ash is recognized at two localities and Aira-Tn ash at four localities in southeastern part of Korean peninsula and Cheju island. These tephras are of great significance in volcanology as well as Quaternary research not only in Japan but also in Korea.