Fig. 5. Fit of the North Atlantic continents after Bullard et al. Structural 

 trends on land : broken lines Appalachian-Caledonian, solid lines 

 Hercynian. Solid lines in mouth of English Channel are magnetic 

 anomaly lineations (Hill and Vine, 1965). 



THE FUTURE 



In the future, during the next few years, there is bound to be 

 great expansion of our attempts to make direct studies of the 

 upper mantle, taking to sea the techniques, such as large arrays of 

 seismometers or strain and tilt measuring devices, that have revo- 

 lutionised seismology on land during the past decade. We need to 

 be able to map the shape of the Moho by reflection techniques and 

 to be able to study the anisotropy and non-uniformity of the 

 properties of the rocks beneath it. 



It is because the oceanic crust is relatively thin and simple 

 compared to the continents, so that it reflects the recent history 

 of the mantle better than the continental crust does, that geology 

 must go on at sea if we are to understand the development of the 

 crust and its structure and resources. 



REFERENCES 



Blackett, P. M. S., Bullard, E. C, and Runcorn, S. K. (Editors), 1965, A 

 Symposium on Continental Drift. Phil. Trans. A. Roy. Soc. Lond. 258, 

 1-323. 



Bullard, E. C. (Editor), 1954, A discussion on the floor of the Atlantic Ocean. 

 Proc. Roy. Soc. A. 222, 287^107. 



37 



