We have also shown a profile of the deflection of the vertical obtained by 

 Von Arx (1966) by the astrogeodetic method. We are not certain of the cause of 

 the discrepancy between Von Arx's profile and our "10x10'" deflection profile. 

 The difference might possibly arise from Von Arx's distance measurement made with 

 Loran A. Our values might also change with a more precise determination of the 

 "10x10'" geoid than we have been able to do in this preliminary study. 



While the gravity anomaly associated with the Puerto Rico Trench is well 

 known, that associated with the Lesser Antilles (Fig. 15) is almost equally 

 important. In the negative gravity belt east of the Lesser Antilles the 10x10' geoid 

 lies about 13 m below the G and L geoid and about 7 m above it over the island 

 platform. 



As described earlier, we used land gravity data in the United States and Canada 

 in the construction of the geoids in the western North Atlantic. In this process we 

 also obtained a geoid over North America and we compare it with earlier astro- 

 geodetic measurements of the geoid (Fig. 15). Comparisons are made with a profile 

 along 35°N obtained by Rice in 1970 (Strange et al., 1971) and with a profile along 

 100°W from Fisher et al . (1967). For all comparisons the geoids were referred to 

 the best fitting ellipsoid of flattening 1/298.25. The "1x1°" geoid, which is 

 referred to an ellipsoid of flattening 1/297.0, was transformed by using the difference 

 curve in Figure 11. For the geoid of Rice and that of Fisher et al . (1967) we 

 adopted the transformations given by Strange et al . (1971) and Gaposchkin and Lambeck 

 (1971) respectively. Systematic differences (which are not of concern to us here) 

 still exist between the "1x1°" geoid and the astrogeodetic geoids. We have added 

 9 m to the "1x1°" geoid profile along 35°N for comparison with Rice's profile. For 

 the comparison along the 100°W longitude we have removed the systematic difference 

 in plotting the curves a-c and b-c (Fig. 16) . 



We note that for the 100°W profile agreement of the "1x1°" geoid is excellent 



23-27 



