plutonic

[Fr. pluton i que.] [PLUTONIAN.] 1. Of or pertaining to Pluto; Plutonian. 2. Pertaining to, or designating the system of, the Plutonists. plutonic-action, s. Geol.: The influence of volcanic heat, and other subterranean causes, under pre ure. ( Lyell .) plutonic-rocks, s. pl. Geol.: Rocks of igneous or aqueo-igneous origin, believed to have been formed at a great depth and under great pre ure of the superincumbent rocks, or in some cases, perhaps, of the ocean. They have been melted, and cooled very slowly so as to permit them to crystallize. They contain no tuffs or breccias like the volcanic rocks, nor have they pores or cellular cavities. Under the plutonic rocks are comprehended granites, syenites, and some porphyries, diorite, tonalite, and gabbro. Tests of age are furnished by their relative position, by intrusion and alternation, by mineral composition, or by included fragments. They belong to all the leading geological periods, even the Tertiary. ( Lyell .)