There's something about introductory textbooks that can be fundamentally misleading. As I plowed through freshman Physical Geology some 36 years ago, I couldn't help but acquire the impression that all of the major problems in the earth sciences had been solved. Yes, there was a chapter about Wegener's conti nental drift hypothesis along with a few other ideas concerning earth evolution - expansion, contraction - and including Holmes' convection cell idea. Once I began to take the field trips and participate in junior-year field camp, I began to suspect that the textbooks had left something...