102 



UPHEAVAL WITHOUT DISLOCATION. 



when iwo parallel upheavals take place (Jig. 268), it sometimes 

 happens that one portion (a) of the formation is cut off, and then 



Fig. 267. Fig. 268. 



Various dispositions of craters of elevation in calcareous formations. 



forms the culminating point of the whole mass, giving the appear- 

 ance of a repetition of certain strata in the same deposit. The 

 central part of the uplifted mass is formed of matters sometimes 

 analogous to those that essentially constitute the formation, and 

 sometimes totally different. 



16. Upheaval and distortion witliout dislocation. The uplift- 

 ing of strata is often accompanied by ruptures, but frequently there 

 is no apparent dislocation. We have already noticed the isolated 

 mounts or hillocks on the Champs-Phlegreens (Jig. 261), and the 

 same is also seen, for greater or less lengths, which then have 

 more or less projecting sides, or anteclinal lines, formed by the 

 uplifted strata on either side, like the dip of a roof; these effects 

 are similar to those produced by crevices ; but acting on strata of 

 a certain degree of flexibility, like the matters placed in the centres 

 of the preceding figures. The Jura mountains present a number 

 of instances of this ; we often see there different parallel ridges of 

 this kind, clearly marked on the simplest maps, which leave be- 

 tween them valleys of greater or less breadth, on the two slopes of 

 which the beds are uplifted. The result is great undulations in 

 the strata, remarked especially in escarpments, produced by diffe- 

 rent ruptures, which cut the ridges in a great many places. These 



Fig. 269. Distortions of the Jura. Valleys from plaiting. 



1R. Is upheaval always attended by rupture of strata? 

 dinal lines? How are undulations in strata produced? 



What arc ante 



