not used in this study that the gravity anomalies in the 5x5° square centered at 

 22.5°N 100. 5°W and in the 5x5° square to the north are higher than the values used 

 in these calculations. The use of corrected values will raise the geoid over 

 Mexico and to a smaller extent in the Gulf of Mexico. Qualitatively we would 

 expect the -10 m and -15 m contours to shift eastwards and the lowest value in the 

 Gulf of Mexico to become slightly less negative. 



In summary, we see that the "1x1° difference" and the "10x10' difference" geoids 

 give large differences in the short wavelengths from the "G and L" geoid based on 

 the 1969 SAO Standard Earth. These difference geoids correlate well with gravity 

 features in the map in Figure 7. The assbciation of geoid features with physiographic 

 features in the North Atlantic clearly points out the usefulness of accurate geoid 

 maps in learning the details of the gravity field in the short wavelength range 

 used for crustal studies. 



ACKNOWLEDGMENTS 



Drs. J. L. Worzel and D. E. Hayes read the manuscript critically. This work 

 was supported by the Office of Naval Research through contracts N00014-67-A-0108-0004 

 and Nonr 266(79); and by grants from the National Science Foundation including grants 

 GA17761 and GA27281. 



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