290 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



shelves, normally some TO fathoms deeper, would have originally 

 represented approximately a 100-fathom curve around the island. 



Possibilities of accounting for the reef- free surface of the guyots by 

 some connection with a glacial epoch were considered and rejected. If 

 reef growth had been inhibited by a glacial epoch, the guyots would 

 have had to have suffered marine planation followed by sudden subsi- 

 dence to below the level at which reef growth would recommence at the 

 end of the glacial epoch — a coincidence which makes the hypothesis 

 very unlikely. The glacial epoch would have had to be a very long one 

 to permit complete planation of the larger guyots. It cannot possibly 

 be referred to the Pleistocene epoch since the Marshall Islands atolls 

 are younger than the guyots and there could obviously not have been 

 time for marine planation, subsidence, and upbuilding of the atolls 



FiGUEE 10. — Profiles across two guyots. A is normal except that the gently sloping 

 shelf is lacking on the right-hand side ; B is an example of the hummocky type 

 of upper surface. 



all in this short epoch aside from the inconsistency that the cold water 

 was called upon to keep the guyot surface reef -free but later on per- 

 mitted the upbuilding of the atolls. 



GENERAL REI^^TIONS WITHIN PACIFIC BASIN 



Since it is difficult to discuss any theory of origin of guyots against 

 the background of misconception and ill-founded theories which at 

 present confound geologic literature on ocean basins and the Pacific 

 Basin in particular, the writer proposes to wipe the slate clean and 

 start on a new basis. 



The Pacific Basin is here considered to comprise the central portion 

 of the ocgan and is bounded by an almost continuous belt of strong 

 late Cretaceous-Tertiary mountain building. On the northern and 

 western borders this belt is characterized by elongate deeps which lie 

 over downbuckles of the earth's crust.* Related island arcs show 



» See the works of Vening Meinesz and others on gravityat sea. 



