BECAUSE of similarity in methods of observation and reduction, it is possible to combine the gravity data of the United States Coast and Geodetic Survey and the Department of Mines and Resources of the Dominion of Canada in large-scale gravity investigations. The combined data include gravity observations extending from lat. 24° N. to 67° N. and from long. 52° W. to 133° W., an extent of 43° in latitude and 81° in longitude. This region includes large variations in topography and in geology, and has considerable coastal regions.