Page:The Journal of geology (IA journalofgeology21894univers).pdf/436

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-

Fig. 1.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 localities is flexed into minute puckerings and minor folds having 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-