way a meandering gorge through the hills and ponded sediments. 

 The permanence of the ocean basins, at that time presumed to 

 have been there for at least 1,000 million years, posed the important 

 question: where have all the sediments gone? In the five years 

 between 1954 and 1959 the seismic layering beneath the ocean 

 basins had been worked out and was summarised by Hill (1957) 

 for the Atlantic: 



A new technique had emerged in the shape of the towed 

 proton magnetometer; on many crossings of the Mid-Atlantic 

 Ridge Ewing and Heezen had discovered the existence of a 

 median magnetic anomaly associated with a median valley. The 

 existence of high heat flow on the Mid Ocean Ridge had become 

 established and the ships of the Lamont Observatory had demon- 

 trated that the position of the Mid-Ocean Ridge system could be 

 predicted from its association with a world-encircling system of 

 earthquake epicentres, as Rothe had suggested at the Royal 

 Society in 1954. Earthquake seismologists working on surface 

 waves had demonstrated that the low velocity channel in the upper 

 mantle predicted by Gutenberg was shallower under the oceans 

 than under the continents. All these advances were reviewed by 

 M. Ewing (Ewing and Landisman in Sears, 1961) at the first 

 International Congress. Bullard, in Sears, 1961, significantly, drew 

 attention again to the problem raised by Lees, of geologic structures 

 which transect the continental margin, and discussed the possibility 

 of continental drift. 



However, one of the main problems was the question of where 

 the sediments had gone, and this reduced to determining the 

 nature of the rocks of layer 2: if layer 2 were compacted sediment 

 it was just possible that the oceanic floor could be permanent, but 

 if it was lava it could not be. The case for believing the seismic 

 second layer to be consolidated sediment was put by E. L. 

 Hamilton (1959; also Sears, 1961) but it has not prevailed. The 

 only abyssal hill yet sampled proved to be of weathered basalt 

 having just the right seismic velocity (Matthews, 1961) and subse- 

 quent calculations to explain magnetic anomalies observed at sea 

 have required strongly magnetised rocks in layer 2. Current opinion 

 regards layer 2 as being volcanic though with sediments inter- 

 mingled. If this is the case then the ocean floors cannot be old — 



31 



