GEOLOGICAL RECORD ON THE OCEAN' FLOOR 133 



during which a position of the North Pole in the North Pacific 

 has been postulated. As Walter Munk has pointed out, this is one 

 of the most interesting applications that can be thought of for 

 some of the drilling tests planned to precede the ultimate attempt 

 for penetration of the earth's crust. 



So far the meridional cross section through the sedimentary 

 strata under the equator, shown in Fig. 2, has been used to 

 demonstrate the possibilities for accurate mapping of polar 

 wandering; however, another interesting feature of the equatorial 

 sedimentation mechanism should also be pointed out. If, instead 

 of investigating the relation between latitude and accumulation, 

 we focus our attention on the variation in time of accumulation of 

 biologically produced materials such as skeletal material of 

 carbonate, silica, or phosphate, or elements such as the rare earths, 

 or zirconium, we find (Fig. 4) that there is a marked variation 

 with time in the amount and kind of organic remains, in the cases 

 shown here, of calcium carbonate and diatomaceous silica. This 

 sequence is repeated in detail along the equatorial strip of high 

 productivity; the section shown in the middle is from north of 

 Marquesas; the one to the left shows the conditions found 5400 km 

 further to the east at the Galapagos Islands. Westward this 

 stratification can be followed to near the date line, and altogether 

 it extends along the equator over nearly one-quarter of the earth's 

 circumference. 



The present time is characterized by a relatively low carbonate 

 content in the sediment whereas during the preceding age, which 

 coincides in time with the last glaciation in higher latitudes, the 

 contribution of organic remains was high. Going downward in the 

 sediment, four or five major maxima of this kind and a number of 

 smaller ones are encountered before the Tertiary boundary is 

 reached, identified by Emiliani on the basis of the markedly higher 

 paleotemperature of planktonic Foraminifera. It has been demon- 

 strated by Bramlette that this change in temperature coincides in 

 time with an evolutionary change in the coccolithophorids, which 

 is recognizable over the equatorial Pacific and probably also 

 elsewhere. The Tertiary strata are characterized by smaller 

 amplitude of the variations in the supply of organic remains to 



