Major structures and tectonics

The association of structures of similar type in regions, zones, or belts, as in fold mountain chains, zones of nappes or of major rift faulting, slate belts, metamorphic zones, and so on, is an outstanding geological fact which leads to the consideration of the regional deployment of major structures, and their spatial relationships one to another. Taken in conjunction with other data such as the distribution of sediments, the kinds of rocks and their thickness, the location of igneous rocks and of zones of metamorphism, regional study leads to a synthesis of geological events in space and time and to an under-standing, as yet far from complete, of the great units and elements in the structure of the continents and oceans. This is tectonics. Ed. Suess’ great work Das Antlitz der Erde was the first major study along these lines, ¹ directing attention particularly to the development of structures along their trend or regional strike as well as in cross-section. Since then geological knowledge has vastly expanded and geophysics has provided an entirely new body of data relevant to the inner structure of the globe, the former distribution of continents in the geological past, and the structure and evolution of ocean basins, which were virtually blank on the geological world map until very recently. Tectonics, from being largely an encyclopaedic exercise in the organization of knowledge, has come to be a positive element in geological philosophy, which may be used to guide regional studies and mineral exploration.