Charles Lapworth was one of the intellectual princes of our profession. He it was who discovered the “Secret of the Highlands.”1 In another Scotland Yard he triumphantly illustrated the British genius for detective work. His penetrating eye saw in principle, and later Peach and Horne proved, the majesty of the Scottish thrusts. Thus a revolutionary idea became generally accepted. Yet a still more vital secret underlies the secret explained by the brilliant Lapworth. That further mystery, still unsolved to general satisfaction, is the cause of the clean-cut slicing and plastic shearing of the rocks when mountains are made. Clearly the data for solving the mystery must be sought under all the lands and seas—in the earth’s vast interior.
There, too, is the condition for the isostatic rise of the crust when the regional ice-caps melted, or when continents lost weight by denudation and rose to renew their equilibrium. . . .