chap. xin. Cleavage and Foliation. 467 



quartz-veins, is entangled in gneiss, in such a manner as 

 to show that it had certainly originated in some pro- 

 cess of segregation : again, in another spot, the gneiss 

 tended to pass into hornblendic schist by alternating 

 with layers of quartz ; but these layers of quartz aln,osb 

 certainly had never been separately deposited, for they 

 were absolutely continuous with the numerous intersect- 

 ing veins of quartz. I have never had an opportunity of 

 tracing for any distance, along the line both of strike 

 and of dip, the so-called beds in the metamorphic 

 schists, but I strongly suspect that they would not be 

 found to extend with the same character, very far in the 

 line either of their dip or strike. Hence I am led to 

 believe, that most of the so-called beds are of the nature 

 of complex folia, and have uot been separately de- 

 posited. Of course, this view cannot be extended to 

 thick masses included in the metamorphic series, which 

 are of totally different composition from the adjoining 

 schists, and which are far extended, as is sometimes the 

 case with quartz and marble ; these must generally be 

 of the nature of true strata. 1 Such strata, however, 

 will almost always strike in the same direction with the 

 folia, owing to the axes of elevation being in most 

 countries parallel to the strike of the foliation; but 

 they will generally dip at a different angle from that of 

 the foliation ; and the angle of the foliation in itself 

 almost always varies much : hence, in crossing a meta- 

 morphosed Schistose district, it would require especial 

 attention to discriminate between true strata of depo- 

 sition and complex foliated masses. The mere presence 

 of true strata in the midst of a set of metamorphic 

 schists, is no argument that the foliation is of sedimen- 



1 Macculloch states (' Classification of Rocks,' p. 364) that prim- 

 ary limestones are often found in irregular masses or great nodules, 

 • which can scarcely be said to possess a stratified shape.' 



21 



