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[chap. 12 



extends for 400 miles along a north-south line, south of the Azores (Fig. 3). In 

 the southwest Pacific, many lines of islands and seamounts cross the ocean. In 

 the mid-Pacific southwest of Hawaii is a large area of seamounts whose flat 

 sunnnits range from 450-850 fm beneath sea-level. These seamounts have been 

 termed "Guyots"'. From the flat summits, shallow-water fossils of Cretaceous 

 age have been dredged (Hamilton, 1956). Such sunken islands are not entirely 

 limited to the Pacific: in the Atlantic, several of the Kelvin Seamounts are 



Fig. 28. Fracture zones of the eastern Pacific compared with trends of archipelagos of the 

 western Pacific. PVacture zones are shown by sohd lines and archipelagos by chains 

 of dots. (After Menard, 1959.) 



flat-topped at 650 fathoms, and the seamounts of the Atlantis-Great Meteor 

 group have flat summits at 150-250 fm. 



The number of seamounts in the sea is of interest in view of tectonics and it 

 can be estimated in the Pacific by several methods converging on the number 

 104 (see Chapter 15). The distribution of large seamounts and volcanic islands 

 is not iniiform. Instead, they are clustered in groups of 10 to 100. Abyssal hills 

 are randomly distributed, however, so that all the sea floor has been the site of 

 vulcanism, intrusions or faulting. The vulcanism has ranged in geological time 



