189 



Hornblende schist, independently of its tran- 

 sitions formerly noticed, is also found, in some 

 situations, to pass into clay slate, or fine argilla- 

 ceous schist ; although I have not observed any 

 instance of a decided alternation or association of 

 distinct beds of those two rocks. In this case, 

 the change from the hornblende into the schistose 

 clay of slate, seems to be effected very gradually, 

 and with great facility. An example of this na- 

 ture occurs in Rossshire. As a converse to this 

 case, it may also be stated, that argillaceous schist 

 sometimes becomes partially, but gradually also, 

 converted into hornblende schist when in the 

 vicinity of granite or of the trap rocks. 



In some of the Western Isles of Scotland, 

 there is an alternation between chlorite schist and 

 hornblende schist, of a very remarkable nature, 

 and accompanied, also, by other strata, such as 

 quartz rock and micaceous schist. In some parts 

 of this series, there is an imperfect gradation be- 

 tween the two former rocks ; produced by an in- 

 termixture of hornblende in the chlorite schist, 

 at length predominating so far as to exclude it. 



