As a result of wide experiences, prolonged study, and many conferences I am convinced that granites, strictly defined, form by cooling of granite magma, by metasomatic replacement of other rocks, and possibly by some intermediate action or mixture of the two processes.

Granite magmas may form from large bodies of basalt magma; or more directly by the melting of part of an earth-zone, characterized by abundant gneisses and granites—a zone that seems to have persisted from early Archean time to the present. The solutions that replace other rocks by granite are partly the granite magmas themselves and partly emanations from such magma; but the suggestion that emanations for this replacement arise from great “unknown depths” throws the discussion into the realm of speculation, which will be unprofitable until we have very strong evidence that large masses of granite result from metasomatism.

The evidences and experiences which have influenced the writer to the views he-now holds are presented in brief.