III. ESTIMATES OF SOURCE BODY 

 Estimates of the probable shape, location, and magnetic properties 

 of the source body were made with a modified computer technique of 

 Vacquier (1962). Given a three dimensional, uniformly magnetized body 

 and the observed anomaly, the program computes a direction and intensity 

 of magnetization. A theoretical anomaly is then determined from the 



computed magnetization and the source body. The difference between the 

 observed anomaly and the computed anomaly is a measure of the "goodness 

 of fit," 



For the Plantagenet feature, the anomalous vertical intensity was 

 used as the input, and two source configurations were tested as possible 

 solutions. The observed topography was discounted as being the source 

 body, due to the localized areal extent of the magnetic anomaly; how- 

 ever, the slope characteristics of the bank were assumed to be a 

 reflection of the source body. 



An east-west and north-south cross section through the center of 

 the first model (run no. 1) is illustrated on Figure 12. The depth to 

 the top of the model was based upon depth estimates from Steam's 

 method (Heiland, 1946), and Peters' method of tangents (1949). The 

 slopes and base were arbitrarily chosen. This model resulted in a poor 

 fit and excessive intensity of magnetization. The second model (run 

 no. 2, Fig. 13) resulted in a better fit with a computed intensity of 

 magnetization of 1200 gammas, and horizontal and vertical directions of 

 339° and 85°, respectively. From the results of run no. 2, it is evi- 

 dent that a body located between the model of Figure 13 and the ob- 

 served topography would yield a closer fit. This is commensurate with 

 the investigations of Officer et al (1952) which indicated that the 

 volcanics beneath the Bermuda Islands are close to the top. Further 

 computations were not made because additional geophysical and geological 

 information is required for a more significant solution. 



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