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The accumulation of physical data such as gravity values and the adjustment of these values to an acceptable absolute standard is usually an endeavor that can best be carried out by a government organization such as the National Bureau of Standards or the United States Coast and Geodetic Survey. That a scientific institution should undertake such a task on an international world-wide basis can only be justified in terms of the requirements of its own scientific research program and the inadequacy of the data available.

That the gravity data available in the United States from government sources were inadequate both in terms of reliability and density of observations for regional geologic studies was evident over twenty years ago. It was for this reason that the senior author in 1939 (Woollard 1943) established the first of a series of gravity and magnetic traverses across the United States with observations at 10-mile intervals to determine the degree to which regional geologic features are reflected in these data. This study was extended in 1941 to include all of the Appalachian tectonic province between Newfoundland and the Gulf of Mexico lying between the Atlantic Coast and the Cumberland-Allegheny Plateau. It was this latter program that focused attention on the fact that the absolute gravity datum in use in Canada was not the same as that being used in the United States, and that there were datum shifts in the pendulum gravity work of the United States Coast and Geodetic Survey as well as random

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