187 



compound, or else the one mineral passing into 

 the other. 



The passage from micaceous schist to chlorite 

 schist is effected with equal facility ; as the con- 

 stituent minerals of both are so nearly allied : and 

 that passage is no less common than is the associa- 

 tion between these two rocks. 



It is more rare to observe transitions between 

 micaceous and argillaceous schists. Yet they 

 occur in several parts of Scotland, both between 

 the fine and the coarse varieties, respectively, of 

 each rock. But the association in position be- 

 tween the two, is much more frequent than the 

 transition ; as it is most usual for them to be 

 separated by a definite boundary. 



Instances of a decided transition between 

 micaceous schist and hornblende schist, are rare, 

 when compared to those that have been described 

 above. They occur in those cases where mica- 

 ceous schist is found to contain hornblende ; and 

 the two rocks are not unfrequently united in al- 

 ternation, without any absolute transition. 



