to predict the pattern of anomalies observed off Iceland (Pitman 

 and Heirtzler, 1966). The rates of expansion of the ridge deduced 

 by this method are in very good agreement with those (1 to 2 

 cm/yr.) suggested by the time scale of continental drift. 



LINEATIONS 



The only adequate way to check how much of the ocean basin 

 floor shows these strongly linear magnetic structures would be to 

 survey a trans-Atlantic strip in detail. In the absence of such a 

 survey, one may compare the existing magnetometer profiles. So 

 far the results are not too encouraging: correlation between 

 adjacent tracks are unimpressive once the immediate vicinity of the 

 ridge crest has been left, but the tracks are too far apart and often 

 too poorly navigated for this to be certain. This method has how- 

 ever revealed a pattern of broad magnetic lineations in the Bay of 

 Biscay, surveyed this summer by R.R.S. DISCOVERY which is at 

 least consistent with the idea that the Bay was formed by the 

 anti-clockwise rotation of Spain as Girdler had suggested on 

 palaeomagnetic grounds. 



ROCKS FROM THE OCEAN FLOOR 

 Fairly numerous hauls of lava from the ocean floor have been 

 described during the past few years and at the International 

 Oceanographic Congress in Moscow there was, at last, some discus- 

 sion of their petrology. On a recent cruise of DISCOVERY several 

 days were spent surveying and dredging a small area on the flanks 

 of the Mid- Atlantic Ridge (at 43 °N„ 20 °W.) where we thought that 

 a section through the oceanic crust had been exposed by faulting. 

 Here a succession of sedimentary pelagic limestones going back 

 to Eocene in age was found overlying a basement of metamor- 

 phosed basalts and gabbros. K 40 : A 10 age determinations put the 

 age of the metamorphism at 55 m.y. ago. This is all consistent with 

 the metamorphism and faulting of the crust having occurred near 

 the crest of the Mid-Ocean Ridge at that time (Cann and Funnell, 

 1966). Studies of this kind could disprove the idea that the ocean 

 floor is growing from the middle if unequivocally old sediments 

 were found close to the ridge axis. Such specimens have been 

 reported recently by Ewing, Le Pichon and Ewing (1966). 



THE CONTINENTAL MARGIN 



On the American side of the Atlantic the Appalachian struc- 

 tures run parallel to the continental margin, but on the European 

 side they run perpendicularly across it, out to sea. If the idea of 

 continental drift is true they must be truncated and continued on 

 the other side (Fig. 5). 



We know remarkably little about the structure under the edge 

 of the continent off the mouth of the English Channel and this is 

 an obvious challenge. 



36 



