CHAPTER X 



METAMORPHISM 



When either sedimentary or igneous rocks have been affected, 

 either in their mineral composition or in their texture or in both, so 

 that their original character is altered- or entirely changed, they are 

 called metamorphic rocks, and the process is known as metamorphism 

 (Greek, metamorphoun, to transform or change). The term, as used 

 here, will be limited to those changes which have resulted from heat 

 or pressure, or both, whether produced locally, as for example by 

 batholiths ; or over large areas by pressure and heat. 



Contact Metamorphism. — The form of metamorphism most 

 easily understood is that produced when sedimentary rocks are cut 

 by great igneous intrusions, such as batholiths. Under such condi- 



H^ARTZ,T E iSS" 



Fig. 334. — Diagram showing the metamorphism produced by a great igneous 

 intrusion upon the surrounding rock. 



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