DROWNED ANCIENT ISLANDS — HESS 



289 



arrived at the hypothesis here presented. Though it explains the facts 

 at present available, it is highly speculative and might easily be 

 wrong. Nevertheless, it seems worth presenting as a working hypothe- 

 sis, particularly since it has many interesting ramifications, some of 

 which would be worthy of investigation even if the parent hypothesis 

 were found to be invalid. 



EXPLANATION OF DEVELOPMENT OF UPPER SURFACE OF GUYOTS 



When the writer first discovered guyots, he supposed that they were 

 drowned atolls. However, this hypothesis proved untenable upon 



Figure 9. — Profile B-B of figure 7 showing normal atoll slope approaching 



Enlwetok from the East. 



further study. A profile of an atoll should show a rise along the outer 

 margin representing the area of active reef growth and should be 

 dished in the middle — the lagoon — unless it were filled in with yomiger 

 sediments. On an atoll, the profile breaks abruptly outside of the 

 living reef and descends in slopes averaging about 25°. There is no 

 feature comparable to the gently sloping shelf found around the flat 

 tops of nearly all guyots. In fact there seems to be no way of account- 

 ing for these shelves unless the guyots had developed in a sea which 

 did not support reef -building organisms. 



It may reasonably be assumed that guyots were originally volcanic 

 peaks. After a long period of time they became stabilized and were 

 eroded down to low relief. At this time they developed gently sloping 

 shelves around them as might be expected in the case of a maturely 

 dissected island. This was followed by a long period of marine 

 planation, unhampered by reef growth, ultimately forming the flat 

 upper surfaces. If marine planation cut the island down to about 30 

 fathoms below sea level, then the outer margin of the gently sloping 



