distributed about the zero line represented by the ship's track in 

 Figure 12. An adjustment of this type is also discussed in Weissel 

 and Hayes (1978) . Since only the relatively short-wavelength anomalies 

 are considered in this interpretation, this procedure has no effect 

 on the conclusions. It is necessary, however, to point out that the 

 "zero line" has no physical significance. 



10 



