by the 100- and 1000-fathom curves (fig. 8) indicate that the source 
of the anomalies is in the basement. Anomaly A, referred to in the 
literature as the "slope anomaly," has been studied in some detail 
in other areas. Since this feature lies near the basement ridge, 
King et al (1961) and Drake et al (1963) used profile matching, based 
on seismically derived topography of the ridge to determine the 
origin of the anomaly. They concluded that compositional changes 
within the basement, rather than topography were the principal cause. 
Watkins and Geddes (1964) related the basement structure to an 
island arc system and attribute the anomaly to both intrusive and 
extrusive rocks withi- the basement. 
The Oceanographic Office has begun a detailed aeromagnetic 
survey of the Atlantic coastal area from Maine to Florida. Questions 
concerning the nature of the coastal anomalies and their relation- 
ship to the continental margins may be more readily answered with the 
data from this survey. 
IV. SEAMOUNT ANOMALIES 
Whereas the features over Zone 3 are related to deep seated 
basement phenomena, the anomalies seaward of the slope are directly 
correlative with bottom topography. The features over the seamounts 
of Zone 1 display total magnetic intensity anomalies (fig. 4) of 
1000-1400 gammas, and the anomalies over the Zone 2 seamounts range 
from 100-200 gammas. The origin of the seamounts is believed to be 
