There can have been few occasions in the past when the President of the Geological Society of London—the mother of all geological societies—has been able to accept the hospitality of that most splendid of daughters, The Geological Society of America. I come bearing most hearty greetings and good wishes from my Society to yours. This meeting celebrates, I believe, the Centenary of the Geological Survey of Canada, and I am honoured to be present at the inauguration of a second century of fruitful geological investigation. Our countries are bound together by the cords— gossamer yet stronger than steel—of a common blood, a common creed, and a common history—we spring from the same roots. But we geologists are bound still closer to one another by devotion to our common science—nothing can unloose that tie. As these proceedings continue, we shall find maybe that we differ on a great many aspects of geological interpretation, but this is a sign of vitality and can in no way affect our regard for one another as fellow-seekers after the truth concerning the crust of Mother Earth. As President of the Geological Society of London, I salute The Geological Society of America and, contemplating your glorious past, I look forward to your yet more glorious future. In the foregoing paragraphs I have spoken in my official presidential capacity; from now on, I speak as a private individual—the personal pronoun will occur, I expect, with astounding frequency. I am not certain...

The hypotheses of the formation of granite by consolidation of magma derived from depth and of granite formed by granitization in association with magma intrusion are accepted as valid concepts. The results of a study of over 2000 square miles of the northwest Adirondack Highlands pre-Cambrian igneous complex are presented, and the two concepts are found far more appropriate to explain the source of the introduced material of the widespread granite masses occurring there than recourse to the hypothesis of “emanations” (hydrothermal solutions, gases, or migrating atoms and ions) from depth. It is concluded that over 85 per cent of the northwest Adirondack granitic rocks are the product of consolidation and differentiation of magma intruded as sheets or phacoliths and that less than 15 per cent is the product of migmatization and granitization of metasediments and amphibolite.

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.

Field features and petrographic criteria for granitic rocks of magmatic origin are listed, and a brief discussion is presented concerning the mode of emplacement and the differentiation of intrusive masses. Transitional facies of granitic rocks of metamorphic origin are described in detail. These facies include replacement dikes, replacement breccias, and metamorphic migmatites. Interpretations of mechanisms of the advance of granitization including geochemical migrations are discussed, not only from the detailed evidence shown by miniature features, but also with regard to the relationship of metamorphic granitic rocks to regional metamorphism. Some aplites, pegmatites, and quartz veins are explained as retrogressive features following granitization. Granitic rocks which exhibit both crystalloblastic textures and marked flow structure are interpreted as examples of rheomorphism, and the term neomagma instead of magma is used for the material that flowed. The use of large lantern-slide (3¼ × 4¼ inches) thin sections has proved to be most helpful in the study of critical features of either magmatic or metamorphic granitic rocks. In these large sections, microtextures and microstructures can be observed much better than in an ordinary thin section, or a number of thin sections, and an integrated overall picture can be obtained.

INTRODUCTION In his well-known essay, The method of multiple working hypotheses, Chamberlin (1897) discussed various modes of attack upon scientific problems. Of a theory hastily advanced in explanation of any group of observations he said, “From an unduly favored child it readily grows to be a master and leads its author whithersoever it will.” The theory thus becomes a “ruling theory.” It might be said that it becomes a prejudice. As we may readily suppose, he regarded the ruling theory as having little to commend it, though he did point out that in the method of the ruling theory the investigator’s “very errors may indeed stimulate investigation on the part of others.” Chamberlin then passed on to consider the method of the working hypothesis, which he naturally regarded as having notable advantages, but added “. . . the distinction is not such as to prevent a working hypothesis from gliding with the utmost ease into a ruling theory. . . ”, and further, “To avoid this grave danger the method of multiple working hypotheses is urged” where “the mutual conflicts of hypotheses whet the discriminative edge of each.” Chamberlin thus had in mind a happy situation where an individual investigator diligently sought all reasonable processes that might lead to an observed relation, carefully considered the full consequences of each process envisioned, impartially compared these deduced consequences with the re-examined facts and thus reached a conclusion as to the probable process or group of processes that were operative. ‘Tis a consummation . . .

R.H. JAHNS (California Institute of Technology, Pasadena, Calif.): Mr. Moderator, Members and Guests of the Society: The five points of view that were expressed this morning concerning the origin of granite are perhaps most striking for their similarity, at least insofar as the introductory remarks were concerned. There seems to be general agreement that some granite was formed by crystallization from magma, some by replacement of pre-existing crustal material, and perhaps some by other processes. The agreement is less pronounced, unfortunately, on the definitions of such fundamental terms as “granite,” “gneissic granite,” “granite gneiss,” and “gneiss.” Although opinions differ little concerning the composition of true granite, questions of texture are by no means so simple. To what extent can metamorphic textures be present in a rock defined as “granite”? To what extent, even, can such textures be identified with assurance? It is clear that geologists are not yet agreed on single answers to these questions. Even the term “magma” gives trouble. Evidently there are those who feel that a true magma should be fluid, or almost wholly so, whereas others would extend the term to include most mixtures of solid and fluid material. A few extremists would take a broad view of this term and would then define granite as any silicic rock formed by crystallization from a magma! For purposes of this discussion, let us take from the statements of this morning an “average definition”, however approximate that might be, for each of these basic terms, and go on . . .