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THE JOURNAL OF GEOLOGY. 



Structural differences. — Evidence afforded by a study of 

 the structure in the two series, both original and induced, 

 has an important bearing upon the separation of the two 

 terranes. Of first importance may be mentioned the relatively 

 orderly strike of the lamination and bedding of the upper 

 series in comparison with the strike and disordered succes- 



FlG. I. Initial development of strain-slip cleavage, dipping to the right in a 

 schistose phase of the conglomerate-gneiss horizon. The fluted bedding planes are 

 seen dipping to the left. Under the microscope the faulting of the sharp crenulations 

 is plainly visible with secondary formation of muscovite along slipping planes. 



sion of the core rocks. The Mendon series in many local- 

 ities is flexed into minute puckerings and minor folds hav- 

 ing northerly pitching axes overturned to the west. Along 

 the western line of the folds, and in synclinal troughs, sharp 

 crenulations are developed ; on the backs of folds stretching and 

 consequent schistosity are best shown. When the sides of the 

 crenulations are forced to move over each other strain-slip clear- 



