SECT. 2] 



OCEANIC ISLANDS, SEAMOUNTS, GUYOTS AND ATOLLS 



371 



clusters of seamounts appear to rise from a relatively level, although irregular, 

 sea floor and in this they are dissimilar from most archipelagoes. The diff"erence 

 probably is not significant with regard to origin, however ; if the seamounts 

 continued to gro\\', lava flows would eventually reach from the base of one 

 volcano to the next and would build a connecting rise. In groups as well as 

 individually, therefore, the seamounts resemble volcanic islands in all respects 

 except size. The close similarity is further emphasized by the existence of 

 intermediate types, namely, guyots, atolls and banks. 



No Vert. Exog 



GILBERT SEAMOUNT 



CONTOUR INTERVAL 100 FM 



Noutical miles 

 6 ~i i 3 4 5 



Kiy. 3. CJilbert. Seamount in the Norlli PaciHc 



4. Guyots 



A guyot is a flat-topped seamount deej^er than 100 fm. The discovery of 

 these features was announced by Hess in 1946 and his pioneering efforts 

 launched a continuing and very fruitful exploration of guyots. Hess personally 

 sounded 20 guyots and found 140 probable guyots by examining unpublished 

 soundings. The guyots described were limited to the northwestern Pacific, 

 although Hess recognized that some of the seamounts described by Murray 

 (1941) in the Gulf of Alaska were also flat-topped. From their topography alone, 

 Hess concluded that the guyots were drowned ancient islands which had been 

 truncated at sea -level. From the absence of coral capping he reasoned that they 



