SUBMARINE MOUNTAINS 63 



classes of anomaly we shall now be interested in only two — the 

 free-air anomaly and the isostatic anomaly. 



Actual measurements of the intensity of gravity have been 

 made on Bermuda, Ascension Island, and Saint Helena Island 

 of the Atlantic, and on Oahu Island and Hawaii Island of the 

 Pacific. In every instance gravity is much above normal. The 

 same is true at the submarine stations occupied by Professor 

 Vening Meinesz off Oahu, Madeira, and Sao Miguel islands. 3 

 Figure 32, a map of Oahu, illustrates one of the cases (land 

 stations only). Gravity stations are indicated by dots, beside 

 which are the corresponding free-air anomalies. Much greater 

 free-air anomalies are found in Hawaii. See Figure 33, where 

 numbers in brackets represent isostatic anomalies. All the 



FIGURE 32. FREE-AIR ANOMALIES OF GRAVITY IN OAHU ISLAND. 

 HEIGHTS IN FEET. 



