The foundations of geology were based on exposed rocks--their lithology, stratigraphy, and structures. However, these rocks cover less than 30 percent of the surface of the earth. In the last few decades much of the remaining 70 percent of the earth has been studied by less direct means, with the result that what we have seen on land does not seem to fit with what we are discovering beneath the world's oceans. However, it seems reasonable that the ultimate forces that have shaped the earth are the same beneath the oceans and within the continents.

These new marine data have aroused serious considerations of the possibility, geometry, and mechanics of continental drift, plate and mantle convection. These concepts seem to account well for the geology of many exposed rocks and for most marine data, but they presently appear to be unrelated to the deformation of large areas of the continents and oceans. It is important at this stage that we carefully examine the history of the continents (and particularly of the present and past continental margins) in light of these growing concepts of global tectonics. Equally obvious is the importance of directly sampling the rocks beneath the deep oceans (through such programs as the Deep-Sea Drilling Project).

The successful exploration and development of natural resources depend ultimately on the soundness of our understanding of the history and structure of the earth. Anything which might improve this understanding is of obvious importance to the economic geologist of today and, perhaps, even more so to the meeting of the immense resource challenges of the future.