IBS 



OUTLINES OF FIELD-GEOLOGY 



PART I 



Fig. 74 the whole of a narrow dyke has been rendered 

 schistose, while here and there it has been attenuated or 

 even ruptured along a plane of more intense move- 

 ment. 



It is thus evident that between cleavage and foil. 

 an intimate connection can be traced. Cleavage may 

 be regarded as the initial stage of the proc\ 

 when completed results in a mineralogiral transformation 



FIG. 75. Foliation of mica-schist and grit-bands coincident with bedding ; rocks 

 subsequently folded. 



and re-crystallisation of the constituents of a rock along 

 certain planes known as planes of foliation. But it 

 is conceivable that foliation may have been superin- 

 duced in planes which were not those of cleavage, or at 

 least, which were older than the later cleavage. Among 

 metamorphosed sedimentary rocks, it can sometimes be 

 demonstrated that the planes of foliation coincide with 

 those of bedding. The same coincidence often occurs, 

 of course, between bedding and cleavage. But even 

 where foliation has taken place along planes of original 



