CONTENTS. 



Page. 



Letter of Transmittal 29 



Chapter I. — Introduction 31 



General nature of alterations 31 



Classification of metamorphism 39 



Geological factors affecting the alterations of rocks _ 40 



Composition _ 40 



Structures and textures 4ft 



Porosity 40 



Water and gaseous content _ 41 



Climatic and geographic conditions _ 41 



Time 41 



Environment _ 49 



Degree of movement 42 



Depth 43 



Chapter II. — The Forces of Metamorphism 45 



Chemical energy 45 



Gravity _ 46 



Mechanical action 4g 



Molecular mechanical action 47 



Mass mechanical action 49 



Permanent strain without openings 49 



Permanent strain with openings 49 



Permanent strain with closing of openings and welding 50 



Water action 50 



Heat and light ~ 51 



Sources of heat and light 51 



The sun as a source of heat and light 51 



Heat derived from within the earth by conduction or convection through water 



or magma 53 



Mechanical action as a source of heat 54 



Chemical action as a source of heat 54 



Effects of heat and light on alterations of rocks 54 



Direct effects of heat and light •_ 55 



Mechanical effects 55 



Chemical effects 5g 



Indirect effects of heat and light 5g 



General statements _.. u 57 



5 



