As the Mid-Atlantic Ridge crest is approached east of 45°W between 25°N and 

 35°N the gravity anomalies and the geoid heights attain positive values. The 

 closed geoid high with a maximum of 0.6 m at 45°N 45°W is also over the Mid-Atlantic 

 Ridge crest. A geoid low with a minimum of -7.2 m is centered near 41°N 42°W 

 over the Newfoundland Basin. 



In the Caribbean area the prominent negative belts associated with the 

 Puerto Rico Trench and its eastern extension around the Lesser Antilles and into 

 Barbados (12.5°N 59.5°W) are clearly reflected in the geoid map. The negative 

 belt along the northern coast of South America is also associated with a low 

 in the geoid. Gravity as well as geoid highs lie over the islands of the 

 Hispaniola and Jamaica and southeast Cuba and continue southwest along the 

 Nicaraguan Rise into Middle America. 



The "10x10' difference" geoid map (Fig. 13) helps to resolve the gravity 

 features even further. A high is apparent over the island of Puerto Rico and 

 lows over the Anegada Trough (east of Puerto Rico) and Dominican Trench (south 

 of Puerto Rico) are resolved. A geoid high lying roughly between 12° and 16°N 

 and 63° and 54°W resolves the Aves Swell. Along the South American margin both 

 the gravity highs over the Dutch Antilles and Las Rocques etc. as well as the 

 marginal lows are seen in the geoid maps. 



A value of -21.5 m in the Gulf of Mexico in the "1x1° difference" geoid 

 indicates the largest departure from the "G and L" geoid. The gravity contours 

 in Figure 7 indicate large negative values. The contours west of 95°W in the 

 Gulf of Mexico are based on reliable sea values even though they are dotted 

 (because they lie in a square where 5x5° average rather than 1x1° average values 

 were used) . However, the values in Mexico are few and unreliable. We also note 

 that the astrogeodetic geoid along 100°W in Mexico (between 20°N and 35°N) lies 

 below the "G and L" geoid, (when adjusted for systematic differences) but above the 

 1x1° geoid. We know from the newer data of Woollard et al . (1969) which we have 



23-31 



