In July, 1953, the writers had an opportunity to survey the geology of Kami-ina, Nagano Prefecture. At that time many dikes were observed in its northern part. This paper describes mainly the chemical aspects of one of these dikes with very notable chilled-margins. Augite-porphyrite dike is intrusive into chert and composite in character, exhibiting very fine grained chilled-margins and a porphyritic central portion. There is no recognizable boundary, but an appreciable difference in composition between the chilled-margin rock and the central-pcrtion rock. The chilled-margins show a higher content of FeO, C
2O, Na
2O, MgO and CO
2, but a lower content of SiO
2 and K
2O, than does the porphyritic central portion. This arrangement of chemical composition may be explained on the theory of crystallization differentiation, except the irregularity of Na
2O content owing to the fact of mainly albitization, carbonization and chloritization. The dark margins ccrrespord to an early stage of crystallization and light central portions of silicic composition correspond to a later period of crystallization.
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