296 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



of pre-Cambrian islands formed by the processes suggested above. 

 Tbe group of guyots with which we have been mainly concerned range 

 from 520 to 960 fathoms (3,120 to 5,760 feet) below sea level. Ac- 

 cepting Kuenen's figures for accumulation of sediments, at least 2,000 

 feet of sediments (solid) would have been deposited in the deep sea 

 since pre-Cambrian time. The great bulk of sediments, however, are 

 deposited along continental margins, on the shelves, slopes, and shal- 

 low epeiric seas. It is almost impossible to estimate the amount of 

 water displaced by these inasmuch as a thickness of tens of thousands 

 of feet may displace only a relatively small amount of water since 

 the bottom of such basins of sediments tend to sink isostatically under 

 the load. These thick prisms of sediments may at a later time be 

 deformed and welded to the continents, thereby enlarging the con- 

 tinents at the expense of the oceans. Certainly these processes have 

 decreased the areal extent of the oceans a considerable if unpredictable 

 amount since the end of the pre-Cambrian. If sediments deposited in 

 shallow waters around the continents displaced only half as much 

 water as deep-sea sediments, an estimate which seems to the writer 

 to be on the conservative side, then one could account for a rise of sea 

 level relative to an oceanic island of 3,000 feet (500 fathoms) since 

 the end of the pre-Cambrian which is comparable to the present depth 

 of the shallowest guyots. Thus we might attribute most guyots to a 

 Proterozoic episode of vulcanism. The occasional, less well-preserved 

 surfaces mentioned in the text, having depths between 1,100 and 1,900 

 fathoms might be older and well back in the pre-Cambrian in age. 



RECOMMENDATION FOR FUTURE RESEARCH 



With the above hypotheses in mind it would be exceedingly interest- 

 ing to drill a hole 5,000 feet deep in the center of a Pacific Basin atoll. 

 It is necessary to avoid the outer margin of the atoll since it may well 

 have built outward over its own debris. From another point of view, a 

 hole drilled on the southern rim of Eniwetok would almost certainly 

 penetrate into the underlying guyot at a depth of approximately 4,200 

 feet. It would be extremely interesting also to make magnetic surveys 

 of a number of atolls to estimate the depth to the volcanic core and 

 perhaps couple such an investigation with seismic and gravimetric 

 work. Bottom samples with the Piggot sampler taken from the flat 

 tops and gentle marginal slopes of guyots might bring up some of the 

 rock of which they are formed, provided these surfaces had been swept 

 completely clean of sediments. Pleistocene to Recent banks in high 

 latitudes where cold water would inhibit growth of reef -forming or- 

 ganisms should be investigated to compare their profiles with those 

 of the guyots. A further investigation of Murray's seamounts in the 

 Gulf of Alaska might furnish some of the missing clues to the origin 



