ORIGIN OF FOLIATED CRYSTALLINE ROCKS 315 
would, perhaps, seem to show that chemical analysis cannot be 
used satisfactorily as a criterion for determining original igneous or 
sedimentary character. It is probable, however, that composition 
may still be employed in this connection, to some extent at least, 
after the magnitude and character of the chemical changes involved 
in the production of schistosity in different rocks become better 
determined. 
