Abstract
IJIRI'S principle based on the dialectic materialism in geological sciences was established in 1949. Since then, the principle has been a guiding one in geological researches, and many fruitful results due to the principle have been accomplished. However in these days, in petrological science, idealism as revealed in the form of rationalism are prevailing and original works are scarcely found. The author states that in petrology the principle must be realized and idealism should be overcome. And, it is also emphasized that in the course of petrological studies, genetical problems of each rock mass and the problems of the development of each rock species in the history of the earth must be combined.
