372 MRNARD AND I, ADO [I'HAP. 1 .") 



were Pre-Canibrian in age. The drowned island hv])othesis has been confirmed 

 re]>eatedly and can no longer he (questioned. On the other liand. the su])])osed 

 age definitely is incorrect. Confirmation of the origin of guyots developed 

 quickly. In 1947, Carsola and Dietz (1052) dredged two guyots in the north- 

 eastern Pacific and found rounded basaltic cobbles which could only have been 

 ])roduced near sea-level. In n>49, the Mid-Pacific Expedition set out to explore 

 guyots in the type locality discovered by Hess. There, in the Mid-Pacific 

 Mountains, the flat tops were surveyed and rounded cobbles as well as an 

 integrated reef fauna of Middle Cretaceous age were dredged from the guyots 

 at a depth of about 1800 m (Hamilton, 1956). Very recently, Eocene reef 

 debris has been found at a depth of about 1000 m on a guyot amid the atolls of 

 the Tuamotu Archipelago, and similar debris of late Tertiary to Recent age has 

 been dredged from guyots on the Nasca Ridge off Peru at a depth of about 

 400 m. 



(iuyots are not drowned atolls even though some are capped w ith reef debris. 

 Profiles do not show the typical steep slopes of atolls but rather the more 

 subdued .slo])es of submarine volcanoes (Fig. 9). In the Mid-Pacific Mountains, 

 coarse rounded l)asaltic debris was dredged with coral from the tops of some 

 guyots. At least in these places, the coral formed low banks which never 

 developed into atolls. The reef-covered guyots of the Tuamotu Archipelago 

 rise only a few hundred meters above a submarine plateau. Consequently, they 

 cannot have a thick coral capping and any growth comparable to an atoll seems 

 ruled out by gentle side slopes. 



An intensive search has shown that the distribution of guyots is world-wide. 

 The existence of guyots in the Gulf of Alaska (Fig. 4) was quickly confirmed by 

 detailed surveys (Menard and Dietz, 1951). Additional guyots in the Emperor 

 Seamounts in the northwestern Pacific were described by Dietz (1954), and 

 new groups of guyots were recently discovered in the South Pacific. Descrip- 

 tion of guyots in the Atlantic has been hampered by classification of soundings 

 but at least three groups exist (Heezen et al., 1959). Two isolated exami)les 

 show that there are guyots in the Indian Ocean (Wiseman and Hall, 195(5) 

 and it may be anticipated that more will be found. (Juyots have not been 

 reported in the Arctic Basin but the Lomonosov Ridge is truncated (R. S. Dietz, 

 in litt., 1959) and truncated seamounts would not be unexpected. 



Despite the discovery of six new groups and many isolated guyots, the total 

 number known differs insignificantly from the total of 160 reported by Hess 

 (1946). A few of the probable guyots of Hess have proved to be seamounts 

 with pointed tops ; many others have not yet been confirmed by surveys. In 

 contrast, all of the guyots reported since have been surveyed. Nevertheless, an 

 increase of only 22 known guyots after 13 years of exploration suggests that 

 the total number in the oceans ])robably does not exceed a few hundred and 

 that at least half of them are concentrated in the central western Pacific. 



Guyots range in depth from 200 m (by definition) to about 2500 m, but most 

 are between 1000 and 2000 m. Even in small areas the peak depths normally 

 are not concordant, suggesting that the guyots were islands at different times. 



