SEDIMENTCARPET 67 



and oceans most of the preceding data have been taken, 

 summarizes his view by asserting that for the present 

 study of major tectonic and geophysical processes the 

 boundary of the Pacific Basin, the so-called Marshall 

 Line, seems to have more importance than any other 

 crustal boundary and to be frequently marked by a 

 sharp, deep-reaching discontinuity, whereas transitions 

 of the Atlantic types usually seem rather gradual.-^ 



In the same volume of the Bulletin of the Geological 

 Society of America there is an excellent paper on sub- 

 marine topography in the North Atlantic by Tolstoy, 

 giving a resume of the results of work done by the 

 Lamont Observatory of Columbia University and the 

 Woods Hole Oceanographic Institution.^ I shall briefly 

 summarize some of the most important conclusions 

 from this paper, insofar as they refer to the Mid- Atlantic 

 Ridge. 



During the German cruises in the mid-twenties and 

 early thirties considerable light was thrown on the na- 

 ture of the Mid-Atlantic Ridge, thanks to echo sound- 

 ings. Especially in its northern parts, north of the 

 Azores, it was found to have a structure resembling that 

 of folded mountains, with more or less parallel ridges 

 running from north to south and separated by deep, 

 almost Alpine valleys. One of the foremost specialists in 

 geotectonics of West Germany, Hans Cloos, who died 

 in 1951, made successful attempts to imitate the shape 

 of the ridge and the Azores Plateau by squeezing a 

 plastic material through a narrow fissure. 



