331 



tion, and straits may originate near the fractures without a subsidence 

 of the geanticline along the axis. The movements near the surface 

 are not equal to those at greater depth. But we su|)pose an extreme 

 case, in which, considering broadly, the portions near the surface 

 move at the same rate as those at greater depth. 



The vertical movement and the ej^ect of erosion. 



Considei-ing that during the movement erosion will continuously be 

 at work in the portions above the sealevel, it will generally be possible 

 to compare in the terminal phase the direction of the geanticliiial 

 axis with the direction of the exposed older strikes. In case of a 

 brief and not very intensive erosion, the tectonic details of a more 

 plastic deformation at greater depths, are still invisible. The intensity 

 of erosion decreases if, as in many rows of islands, the deform- 

 ation of the geanticline takes place near the surface of the sea, 

 and it is especially, when the vertical component of the rate of 

 movement is great, that the tectonic details, which have been formed 

 by a more plastic deformation at gieater depth will soon be visible. 



Rectilinear old strikes and curved fjeajiticlinal axis witli a hending- 

 point in the last phase of movement under consideration. 

 The two extreme cases, mentioned above are : 



1. No horizontal movement at the surface. 



In the case represented by tig. 4 the old strikes cut tiie geanti- 

 clinal axes of the terminal phase on either side of the bending-point 

 of A' B' at an angle of about 45°, while nearer to A' and B' the 

 older strike will gradually coincide with the new geanticlinal axis. 

 If we assume that in the portions AC and DB, the movement has 



J)' 



■^3' 



- '■ -y - 



c 



Fig. 4. 



Older strike. 



A C B = horizontal projection of the geanticlinal axis in the initial 



stage of the movement under consideration. 

 A^ C' Di B^ — Ibid, in the last phase of the movement under 



consideration. 



