169 



bending point it may be concluded that velocity differences in a 

 liorizontal direction are a characteristic of the present movement. 



In the Central Atlantic Ridge there is a distinct bending-point 

 between the island of St. Paul and the Romanche Deep, while quite 

 close to it there is a zone of strong seismic activity. Further appli- 

 cation of the comparative method would lead to the conclusion that 

 the Central Atlantic Ridge is not only moving now, but has been 

 moving for a long time, with velocity-differences in a horizontal 

 direction. The tectonic structure of the ridge is not accessible to 

 observation. However, there are indications that a further application 

 of the comparative method is possible. The morphology is still little 

 known, but the soundings have pioved the existence of very great 

 depths, viz. in the Romanche Deep, where a depth of 7370 m. has 

 been sounded. 



This depth has been considered as a remarkable phenomenon 

 for the Atlantic Ocean. The situation close io the heiidiiig-poini poluis 

 to an origin such as already previously suggested by us with regard 

 to abnormally deep straits near the bending-points of rows of islands. 

 Just as is the case in Manipa Strait between Cerani and Boeroe. 

 The Romanche Deep can be explained by difference in \elocity of 

 horizontal movements for neighbouring parts of the ridge along 

 the axis. 



We only find the results of the ditferences in velocity in a hori- 

 zontal direction, the absolute horizontal movement cannot be inferred 

 from the surface characters with the comparative method. We do 

 not know whether the Cejitral Atlantic Ridge originally had a more 

 rectilinear form. Neither do we know whether the bending of the 

 strong curve between the Azores and the island of St. Paul is still 

 increasing, or whether the southern portion with Ascension and 

 Tristan da Cunha is moving with less velocity than the northern 

 in a western, or in an eastern direction, or whether it has become 

 stationary now. 



Many widely different views have been brought forward concerning 

 the origin of the Central Atlantic Ridge. Some authors') look upon 

 it as a rising geanticline, as a mountain range in statu nascendi. 

 Up to now these authors never considered the horizontal movements, 

 which as evidenced before often are much more important than the 

 vertical movements in rising geanticlines. Another explanation') has 

 been afforded representing the ridge as the filling of an originally 



') E. Haüg, Traite de Geologie I, 1907, p. 164. 



*) A. Wegener, Die Entstehung der Kontiuente und Ozeane. 1922, p. 42. 



