802 HORNBLENDE SCHIST. 



rock. In other cases, however, the former equals, 

 or even exceeds the gneiss in quantity, so that the 

 term subordinate is in no rational sense applicable 

 to it. Whatever theoretical views may be im- 

 plied in this term, they are not matters for inquiry 

 in this place. 



Where it occurs in this association, it com- 

 monly follows all the contortions of the gneiss, 

 and is traversed by the same granite veins: a 

 fact which only proves that these veins are poste- 

 rior to the whole series. In other cases, horn- 

 blende schist may follow gneiss without exhibit- 

 ing that appearance ; which equally proves that, 

 in these, it is posterior in origin to the time at 

 which the granite veins penetrated the inferior 

 strata, It is also found, but less conspicuously, 

 in Scotland at least, interstratified with those va- 

 rieties of gneiss, formerly described, which are 

 more evenly disposed and contain no granite 

 veins. In all these instances it passes into the 

 gneiss by alterations in the proportion of the 

 leading ingredient, hornblende, and by the ac- 

 quisition of the quartz which is nearly essential 

 to the composition of that rock. 



