SECT. 1] 



GBAVITY AT SEA 



167 



1959a). At the top right of each cross-section is shown the continuous free-air 

 anomaly curve observed with the Graf Sea Gravimeter. Gravity anomahes in 

 the region indicated that the normal anomaly in the vicinity of this seamount 

 would be about -38 mgal. In Case A it is assumed that the seamount is super- 

 imposed on the sea crust and sediments, and the three computations represent 

 density assumptions of 2.30, 2.50 and 2.84 for the cross-hatched mass shown 

 in the diagram to the left. In Case B, the more logical view that the seamount 

 is based at or near the base of the sedimentary layers is computed for the same 

 density assumptions. In Case C, a local isostatic compensation is assumed at 



C a r y n 



Seamount 



Km 



3C 



N 



Sorlh 

 20 



of 36°27 S' 



30 20,. 



Regional Anomaly -5510 '40fngal 



^15 



Fig. 25. Computed curves for various structure sections of Caryn Seamount. (After 

 Worzel and Talwani, 1959a.) 



the base of the crust with a density the same as that for the 6.75 km/sec crustal 

 layer which overhes the M-discontinuity. The densities for the various layers 

 determined by refraction seismology were chosen according to the Nafe-Drake 

 velocity-density relation (Talwani et al., 1959). 



Using the criterion of the removal of the anomalous feature, one would 

 choose a solution of a density near 2.50 for Case A, the solution of a density near 

 2.30 for Case B, or the solution of a density between 2.30 and 2.50 for Case C. 

 The remaining fluctuations of the curves in each case are probably due to an 

 imperfect knowledge of the shape of the body, or due to the fact that the 

 density may not be well represented by a mean density, or to the errors of 

 calculation ; or perhaps due to the errors of measurement caused by an im- 

 perfect knowledge of the ship's velocity. 



Most workers have accepted a Case A type of solution. In view of the evidence 

 of the core on the flank of the seamount a solution of type B or type C is more 



