At the Cambridge (1932) meeting of the Geological Society of America a statement was made of the general problem which the writer is investigating cooperatively with the United States Coast and Geodetic Survey, and progress was reported. In 1932, thirty-seven gravity stations had been carefully located by W. T. Thom, Jr., W. H. Bucher, and the writer, and the gravity anomalies for these stations were determined by the United States Coast and Geodetic Survey. A striking relation was found between the isostatic anomalies and the elevation of the upper surface of the pre-Cambrian terrane.1
From this relation it was apparent that the density of the superficial rocks near a station was an important factor in producing the gravity anomaly. That this should be so was, of course, to be expected, but quantitative results were sought. The problem was to compare the gravitative pull of the actual rock formations with . . .