14 G. F. BECKER FINITE STRAIN IN ROCKS. 



Page. 



Meaning of Hooke's Law 38 



St less System 40 



Lines of unaltered Direction 4:! 



Properties of Matter 44 



Viscosity 44 



Flow 4o 



Relation of plastic Solids to Fluids 46 



Rupture 48 



( ideological Applications 4i» 



Cases to be considered 49 



Effect s i if direct Pressure 50 



Rigid Disk in resisting Medium .">:; 



Inclined Pressure arid yielding Medium 55 



Inclined Pressure and unyielding Resistance . 56 



Partial Theoiy of the Spacing of Fissures 57 



Examples of inclined Pressure 61 



Distortion on Planes of maximum Strain f>4 



Various Results of Strain 65 



Theory of slaty Cleavage 66 



Influence of Shock 66 



Secondary Action on ruptured Pocks 68 



Effect of tensile Stresses 68 



Review of Theories of slaty ( Jleavage 71 



Why needful 71 



Origin of Jointing 72 



Jointing and Cleavage 75 



Phenomena of slaty Cleavage 7"> 



Theories of slaty Cleavage 77 



( tbjections to Plypothesis of Heterogeneity 79 



Analysis of Experiments 80 



P>ehavior of included Grit Beds and Fossils • . 83 



Conclusions as to Slate 86 



Summary 87 



Phenomena and Plan of Discussion. 



Eoidences of Movement. All observers are aware that few. rock masses 

 are continuous for any considerable distance. It is seldom that more 

 than a few yards of a rock exposure can be examined without revealing- 

 joints, fissures or slickensides. Still more frequently rock masses show 

 slaty or schistose cleavage* impressed upon them by dynamical causes. 

 In a very great proportion of such cases a little attention also discloses 



♦ Schist and the adjectives derived from it are used in literature in somewhat variable senses. 

 As I use it, schist denotes eleavable rocks which an- allied to slates, but in which tin- cleavage 

 surfaces arc not all sensibly parallel to on< another as they air in true slate. By no means are 

 schists all crystalline of metamorphic. 



