Peridotite xenoliths and essential ejecta from the Ninomegata crater of the Megata volcano, Northeast Japan arc, were described in detail. The peridotites have a wide spread of Cr # (=Cr/(Cr+Al) atomic ratio) of chromian spinel, from 0.10 to 0.45, almost comparable with but slightly lower than that of the Ichinomegata peridotites. They often have a secondary hydrous mineral, pargasite, replacing primary minerals. One of lherzolites has several small veinlets of hornblendite. The amount of pargasite is far smaller than that from the Ichinomegata peridotites. The Ninomegata peridotite xenoliths, therefore, preserve characteristics of primary mantle restite; they are in the olivine-spinel mantle array and the Fe³⁺/(Cr+Al+Fe³⁺) atomic ratio of chromian spinel is not high (<0.05).
     Petrographical and/or chemical variety of peridotite xenoliths decreases from Ichinomegata to Sannomegata through Ninomegata within the Megata volcano.
     The essential ejecta from the Ninomegata crater has almost the same characteristics as those from Ichinomegata in terms of petrography and bulk chemistry.

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Physical and chemical processes of partial melting and melt separation have been described based on the petrographical studies of amphibolite-migmatites of the Hidaka metamorphic belt. Melting texture is represented by the crystallization of idiomorphic plagioclase with oscillatory zoned structure. Amphibolites of zones D (low grade part of the granulite facies) and F (high grade part of the granulite facies) had melted and the melt had crystallized as leucosome. Meltpocket and stromatic leucosome are common in basic migmatites of zone D, and leucocratic crosscut veins are developed in zone F. Zone F amphibolites are higher in the volume percent of leucosome than zone D amphibolites, which indicates that the degree of melting of zone F amphibolites was larger than that of zone D amphibolites. Melting reactions took place in a state of disequilibrium, because the restitic plagioclases were heterogeneously dissolved in composition. Melt was trapped in the grain-boundary as a micro-network. As melt-volume had increased, a form of melt-reservoir changed from a chain of melt-pockets through stromatic leucosome to leucocratic vein in basic migmatites.
     Plagioclases which crystallized from melt have two types of zonal structure. One has a core of seed-crystal which was derived from a restitic plagioclase. The other has a complicated growth zoning which is due to the multi-stages of crystallization and a dissolution-texture. The plagioclase composition becomes sodic from core to rim in general. Melt composition had changed many times as often as trapped melts linked each together. Leucosome has experienced the crystallization-differentiation and the segregation of melt in the disequilibrium state.

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Tertiary lignites in two provinces of northern Thailand are preliminarily examined. The results of microscopic and chemical analyses of the samples suggest their accumulation under wet condition and coalification influenced by post-depositional igneous activity. Further detailed investigations will possibly clarify their characteristics distinguished from those of other island arc coals.

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