232 



STRUCTURE COMMON TO ALL ROCKS. 



powerful horizontal squeezing. This is the case with the great slip in 

 Southwestern Virginia, represented in Fig. 196. These are called re- 



Fig. 203.— Section across Yarrow Colliery, showing the Law of Faults (after De la Beche). 



verse faults. In several hundred cases of great fissures, examined by- 

 Phillips, in England, nearly all followed the law of normal faults.* Fig. 

 203 is a section across Yarrow Colliery, in which all the slips follow 

 this law. Of the numerous slips figured by Powell, Gilbert, and Howell, 

 as occurring in the Plateau and Basin Eange region, nearly all follow 

 this law. Fig. 204 is a section illustrating this fact. 



East 



Fig. 204. — Section of Pahranagat Range, Nevada, showing the Law of Faults (after Gilbert). 



nearly 

 struct- 



Explanation of the Direction of Slipping. — Reverse faults are 

 always found in strongly-folded strata such as characterize the 

 ure of most moun- 

 tain ranges, and are 

 evidently formed 

 by powerful lateral 

 pressure. The 



manner in which 

 folds are pushed 

 over until they be- 

 come reverse faults 

 is shown in the ac- 

 companying figures 

 (Fig. 205, A, B, and 

 C). In extreme 

 cases the fault- 

 plane becomes near- 

 ly horizontal, C. 

 These are called 



tlirti o/ rnlnnoQ Fig. 205.— Diagrams showing how Reverse Faults are formed (after De 



mrilbl-pianes. Margerie and Heim). 



* Phillips's Geology, p. 35. 



