34 THE OCEAN RIVER 



method Pettersson calculated the layers of ooze in a few parts 

 of the Atlantic to be nearly 12,000 feet thick. From our knowl- 

 edge of the present rate at which the slow rain of plankton 

 skeletons and other minute particles are added to the sedi- 

 ment carpet of the ocean floor, some have estimated that this 

 thickness represents a period of several hundred million years 

 during which the ocean floor has been submerged. 



Our story of the long history of the sea floor is perforce scat- 

 tered with ifs and buts. No one was present in the distant past 

 to leave an eyewitness account, and the deductions we draw 

 from the evidence of rocks are based on all too few observa- 

 tions. The sea floor at a depth of several miles is only now 

 beginning to yield up its secrets to such indirect probing as 

 the use of explosive depth charges. One of the newer tools 

 which enables us to observe the ocean bed more directly is the 

 deep-water camera; and even television has been used in mod- 

 erate depths. The coring tube, a long metal pipe with compli- 

 cated attachments, has been lowered in depths of thousands 

 of feet and has penetrated into the mud and ooze by as much 

 as 70 feet. The material brought to the surface by this device 

 may give a record of the sediment rain for a hundred thou- 

 sand years or more, depending on the rate at which it was 

 deposited. Seismological stations throughout the world record 

 the time of earthquake shocks, so that we may calculate their 

 speed of travel through the earth's crust and so, by a process 

 of deduction, form some idea of the distribution of heavier 

 and lighter rocks. The pendulum, which we have already men- 

 tioned, tells us where gravity force is greater or less than the 

 average, so that we are able to find out something of the 

 gigantic strains that are warping the earth's crust. 



In recent years much of the widespread interest in the ocean 

 floor has become centered on the mid-Atlantic Ridge which 

 runs southward beneath the seas like a great 7,000-mile sub- 

 marine mountain chain from Iceland in the north to Bouvet 



