CHAPTER XX. 

 DEFORMATION OF ROCK MASSES. 



Having in the preceding chapters dealt at length with the subject 

 of rock formation or Litlwgcncsis, we must next turn our attention 

 to the subject of rock deformation or Orogenesis, i. e., the making 

 of mountain structures. 



As the result of rock deformation a number of distinct struc- 

 tural features come into existence, some of which have already 

 been noted in the preceding chapters. Deformation may be classed 

 as endogenetic or exogenetic, i. e., produced by internal or external 

 causes, respectively. Internal causes are diagenetic, such as chemi- 

 cal change, recrystallization, etc., while external causes include 

 pressure and motion due to gravity, to tectonic disturbances, etc. 

 The following types of deformation may be considered : 



I. Endogenetic. 



1. Endolithic brecciation. 



2. Enterolithic structure. 



3. Contractive joints (prismatic) (basaltic).' 



n. Exogenetic. 



A. Gravitational Deformations. 



a. Structures Due to Movement. 



4. Intraformational brecciation. 



5. Gliding deformations. 



6. Surface deformation through creep. 



b. Structures Due to Compression. 



7. Squeezed-out strata. 



8. Shaliness. 



9. Slatiness. 



c. Of Complex Origin. 



10. Pressure sutures and stylolites. 



11. Cone-in-cone structure. 



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