304 HORNBLENDE SCHIST. 



takes place, it is sometimes observed to pass into 

 it by an insensible gradation. An example of 

 this association is visible in the mountain Ben 

 Lair already quoted. 



It must lastly be remarked, respecting its geo- 

 logical associations, that it accompanies that rock, 

 so little distinguished from it, which has been 

 placed in a separate chapter by the name of ae- 

 tinolite schist, and that the two pass into insen- 

 sible gradations. 



The forms of the strata of hornblende schist 

 require no further detail than that already inci- 

 dentally given in speaking of its associations ; nor 

 does it, in the greater number of these, present 

 any varieties of structure requiring particular de- 

 scription. 



But in those varieties which occur in associa- 

 tion with chlorite schist, in that which is here 

 called the chlorite series, the beds often present 

 a prismatic structure which may be a source of 

 great difficulty to geologists. That difficulty is 

 materially increased by the texture and compo- 

 sition of the rock, which are, in these instances, 

 not distinguishable from those of many green- 



