232 SYNOPSIS OF GNEISS. 



gneiss, or containing some substance not included in that 

 definition. 



A. Quartz and felspar ; simply laminar and at the same 



time granular. The foliated disposition here results 

 from the crystalline position of the felspar. 



B. Hornblende and felspar, foliated and sometimes im- 



perfectly schistose. Analogy and geological con- 

 nexions claim a place here for this rock ; it is however 

 the primitive greenstone of some and the hornblende 

 schist of other authors. 



C. Felspar and mica. Long island. 



D. Felspar and clay slate. Isla, Lewis. 



E. Felspar and chlorite schist. Gigha, Sky. 



F. Felspar, quartz and chlorite schist. Sky. 



G. Felspar, quartz and clay slate. North Uist. 

 H. Felspar, quartz and talc. Scalpa, (West.) 



I. A granular mixture of felspar and quartz in one lamina 



and clay slate in another. 

 K. The same with chlorite schist or greywacke slate instead 



of clay slate. Sky. 

 L. Compact quartz with imbedded grains of felspar, in one 



lamina, and the same schists in the other. Sky. 

 M. Schistose felspar containing crystals of hornblende 



interspersed. 

 N. Actinolite occupying the place of hornblende. 



Sutherland. 



Of all these I may remark, that the geological position 

 and general features are the same as those of the most 

 regular gneiss, and that they often pass into the regular 

 varieties.* 



* It is perhaps superfluous to remark, that although I have thus 

 distinguished the varieties of gneiss by fixed divisions, there are, as in 

 all cases of compound rocks, intermediate gradations which cannot 

 be decidedly referred to either. But I may observe that many other 

 combinations probably exist, and that an ideal catalogue of much 

 greater extent might easily have been formed. The present enumera- 



