884 



PRINCIPLES OF STRATIGRAPHY 



These intersecting fissures are locally known as earthquake "que- 

 bradas." 



Fissures often o]:)en and close repeatedly, even during the same 





Fig. 240. Small earthquake fissure and fault in the Arizona desert. 

 (After Branner.) 



disturbance ; sometimes in closing, the walls are pressed violently 

 together, while shattering of the adjoining rock masses occurs, with 

 the formation of autoclastic material or fault-breccias. This gen- 



.» n n I 'I ' 



I K I. '^ 



"jTi — ^0 'I ^' - 

 '■ -fTi >i^ n lu ^ , 



Fig. 241. Section of one of the sandstone pipes in limestone on the eastern 

 coast of Anglesey in Wales. (After Greenly, from Hobbs.) a, 

 cherty limestone ; /3, sandstone pipe ; 7, cherty limestone. 



erally falls into the fissure, more or less filling it, or it marks the 

 sides of the fissure for some distance outward. 



Filling of the Fissures. Sandstone Dikes. Fissures formed by 

 earthquakes may remain open for a longer or shorter period of 



