Natural History of Granite

Abstract

FOR a century and a half the origin of granite (including granodiorite) has remained one of the most intractable and controversial of the problems geologists have tried to solve. Fouqué and Levy's comment in 1882, that "it excites the most lively discussion", is as true to-day as ever before; and indeed might be regarded in some countries as a mild understatement of the passions that are aroused by apparent conflicts of evidence and very real conflicts of opinion. Hutton clearly established the status of granite as a crystalline plutonic rock, but the French geologists and Lyell and his followers soon realized that not all granites are necessarily of igneous origin. Some occurrences were seen to have no sharp contact against the aureole of metamorphic rocks, but to merge into the surrounding schists through a transitional zone of gneisses and felspathized schists so gradually that at no point could it be said that the rock ceased to be metamorphic and became igneous. These granites consequently came to be regarded, not as representing the cause of metamorphism, but as being the extreme products of its action.