The necessity of revising the first edition of this text so soon after writing it demonstrates very well the dramatic rate at which igneous petrology advances. In preparing this revision, the amazing scope of the changes in own time. Indoctrinated with a reverence for the work of bowen, daly, wager, and their peers, i had little doubt that, armed with my powerful array of tools-rock hammer, microscope, phase diagrams, and chemical analyses-i could deal with most of the volcanic and plutonic rocks of the world. Now, i have more tools but far less assurance that i can use them to explain all rocks. Having seen so many cherished notions discredited.