MECHANICS OF FORMA TION OF ARCUA TE MOUNTAINS 179 



Fig. 18. — Diagram to illustrate the 

 initiation of new anticlines in series. 



and hence devoted to lifting the load, can no longer be thus turned 

 out of its original course and is therefore more or less completely 

 transmitted through the anticline to the still unfolded section of the 

 stratum beyond (Fig. 18). At this point, therefore, the anticline 

 has the effect of temporarily at least stiffening the stratum locally 

 and so extending the reach of the deforming stress. Since, however, 

 some energy is lost in the continued deformation of the original 

 anticline, the new reach beyond 

 the farther base will generally 

 be less than that when the 

 first anticline began to rise. A 

 second arch thus tends to form 

 behind the first, but one of 

 somewhat smaller dimensions. 



This second anticline having in its turn risen to the stage of under- 

 turning, conditions for the development of a third enter; and the 

 process may go on until continued diminution of the reach due 



to imperfect stiffness of the 

 anticHne series brings the pro- 

 cess to an end. 



Successive anticlines thus de- 

 veloped in series are character- 

 istic of Willis's experiments so 

 often cited, and may be repre- 

 sented schematically by a in 

 Fig. 19, where anticlines and 

 synclines alike are developed 

 above the original position of 

 the stratum. Thus it is seen that though series of arcs develop in 

 order from the central area of the series outward, the series of 

 anticlines within each arc develop in the reverse order, or from 

 without inward toward the central area. 



Conditions oj formation of plunging crowns and recumbent folds . — 

 The peculiar curves of unsymmetrical anticlines show clearly that 

 the horizontal external forces which produce them are so resolved 

 as to produce rotation, and in such a sense that the base of the arch 

 is pushed backward under the crown. This is equivalent to saying 



/V— 



Fig. 19. — Correct (o) and two incorrect 

 {b and c) representations of anticlinoria. 



