HYPOTHETICAL STAGES LEADING UP TO THE KNOWN ERAS. 129 



plane of reference, not to absolute distance from the center of the earth. Rightly 

 understood, these are proper terms, dynamically, since it is the relation of part 

 to part that produces the distortional effect. There is a very closely related 



Fig. 32c. — Diagram illustrating the supposed elements of a general deformative move- 

 ment. SS represents the outline of the sphere at the ocean level before deforma- 

 tion. The dotted line represents the corresponding surface of the lithosphere, the 

 ocean basin occupying the center and the continents the flanks. S'S' represents 

 the outline of the sphere at the ocean level after deformation, the heavy line repre- 

 senting the outer surface of the deformed lithosphere, and the space between SS 

 and S'S' representing (much exaggerated relatively) the vertical shrinkage which 

 is the great feature of the movement but is only made apparent through its de- 

 forming effects. That part of the outer shell which is beneath the ocean is sup- 

 posed to descend without much compression, while the necessary folding is con- 

 centrated on the borders of the continent. The central portion beneath the ocean 

 is represented as descending directly toward the center. The portions on each 

 side preserve their length by thrusting laterally and hence descend along paths 

 represented by the arrow-headed lines of which those at the border of the ocean 

 a, a', are the most oblique and represent the greatest thrust. On the borders of 

 the continent the crust is folded to the extent of this lateral thrust. This of course 

 only holds true when the thrust is limited to a single oceanic basin. The lateral 

 thrust is chiefly felt in the outer shell or rigid zone, RZ, which embraces the heavy 

 line and the dotted zone below. Beneath this lies the shear zone, SZ, whose foliated 

 structure is represented as not unlike that of the "drag" belt of a fault plane. 

 The igneous sheets, batholiths, etc., which are supposed to especially affect this 

 zone, are not represented. The great sector beneath the ocean is represented as 

 having crowded slightly upon the sectors beneath the continents on either hand, 

 this crowding being represented by the short arrows b, b'. By comparing bb' with 

 aa' the reason for the shear zone will be made apparent. On the right-hand side 

 the outer part of the sub-oceanic sector is represented as crowding upon the con- 

 tinental sector an exceptional amount, as represented by the deflection of the 

 line b'b". This gives rise to the plateau at the right. The proportions of most 

 of the significant parts are necessarily exaggerated relatively. 



conception, which needs, however, to be distinguished from this, that of the 

 shrinkage (settling) of the general crust away from certain portions, leaving the 

 latter protuberant. Such areas, left above their surroundings by circumjacent 

 depression, have been called horsts. 1 While the existence of horsts is not ques- 

 1 Suess, Das Antlitz der Erde, p. 167. 



