Geology. — "Fractures and Faults near the Surface of Moving 

 Geanticlines. III. The Horizontal Movement of the Central- 

 Atlantic Ridge". By Prof. H. A. Brouwkr. 



(Communicated at the meeting of January 27, 1923). 



Many explanations that have been given for tectonic structures 

 are unsatisfactory on account of the geometrical treatment of the 

 problems and a preference to vertical movements. The geometrical 

 treatment draws attention to the change in position of parts of the 

 earth's crust, while the velocity' of the movement receives no further 

 consideration. Because of the predilection for vertical movements we 

 often explain the observed facts by vertical movements, until it is 

 proved thai faulting must have been effected in another direction. 



In regions, which are not accessible to direct observation, i.e. 

 the parts of the earth's crust covered by the sea, the existing mor- 

 phology is explained by rising and by subsiding movements, while 

 the factor lime is neglected. Subsidence of continents and subsidence 

 of "land-bridges" are common expressions in geological literature. 

 Velocity and direction of the movement are hardly or not at all 

 considered in these inadequate interpretations of dynamic phenomena. 

 The reason is obvious, the forces causing the movement are unknown, 

 and the velocity of the movement cannot be measured. 



Another way of studying these problems is the comparative-tectonic 

 method. Our object in this paper is to consider the results achieved 

 by applying this method to the movement of a region, which is 

 almost entirely covered by the sea, of which the morpiiology is 

 known in broad outlines, and which is still moving, as we know 

 from numerous earthquakes. It is the S-shaped ridge, of which the 

 existence has been proved by numerous soundings and parts of 

 which emerge from the sea, as e.g. the Azores and the islands of 

 St. Paul and Tristan da Cunha. In previous papers ') we pointed to 

 the significance of the bending-points of the horizontal projection 

 of a geanticlinal axis for a judgment upon the horizontal movement 

 of geanticlines. Transverse fractures, which may be lïiore or less 



1) These Proceedings XXlil, p. 570; XXV, p. 327. 



H. A. Brouwer. The horizontal movement of geanticlines and the fractures 

 near their surface. Journ. of Geology. 1921, XXIX, p. 560 — 577. 



