The Sambagawa metamorphic belt in the Hiroishi area，eastern Shikoku，is divided into four geotectonic units based on the lithology in ascending order of the tectonic level i．e．the Units A，B，C and D．The Unit B is subdivided into the Units B1 and B2 on the basis of the size of the albite porphyroblasts．The boundary between the Units B1 and B2 is probably of fault contact．The lower part of the Units B2 shows the metamorphism of the upper chlorite zone to the gamet zone．The other portions of the Sambagawa schists of the Hiroishi area were suffered the chlorite zone metamorphism．
The basic shists in this area are divided into two types．One is basic schist with crossite or magnesio-riebeckite，and the other is that with glaucophane or crossite．The boundary between the distribution of two types of the basic scists is probably located close to the boundary between the Units B1 and B2．Based on the chemistry and the zonal structure of the alkali amphiboles in the basic schists above and beneath the boundary，two different P-T paths are suggested in this area．