THE STRUCTURE OF THE EARTH 



263 



tween Albany and Little Falls one passes over nine easily recognized 

 faults and probably over many smaller ones. 



The term graben (Fig. 257) is used for a portion of the earth's 

 crust bounded by faults, which is depressed relative to the surround- 



Fig. 256. — A section from east to west across the plateau north of the Grand 

 Canyon, with a bird's-eye view of the surface. The effect on the topography of the 

 great faults, folds, and monocline are well-shown. (Powell.) 



ing masses, and the term horst for a section which is elevated relative 



to the surrounding masses and separated from them by faults. The 



Rhine valley, between Basle and Mainz, is an excellent example (Fig. 



81, p. 100) of a graben. 



Here the valley is limited 



by parallel faults, the 



Black Forest lying on the 



east and the Vosges on the 



west. The valley occupied 



by the Jordan River and 



the Dead Sea of Palestine 



is a graben in which a fault 



block has sunk 2600 feet below the level of the plateau, depressing it 



in places below the level of the sea. 



Reverse or Thrust Faults. — In reverse faults the hanging wall 

 should be considered as having moved up, and we thus find that 

 instead of a stratum being separated as a result of the faulting, 

 the two ends overlap so that the older beds are pushed over the 



HORST 



Fig. 257. — Block diagram showing the appearance 

 and origin of a grabert and horst. 



A B C 



Fig. 258. — A fold passing into a thrust fault. (Heim.) 



