MICACEOUS SCHIST. 159 



connected with quartz rock, by its ingredients and by 

 its structure, so it is often united to it in geological 

 position ; either preceding or following, as far as suc- 

 cession or precedence can be determined respecting 

 those primary strata which, occupying high positions, 

 are sometimes reversed on different sides of the per- 

 pendicular. It also alternates with that rock in equal 

 and smaller beds, so that a given tract or mass cannot 

 be preferably referred to either ; while, further, it 

 forms occasional beds in the larger masses, or else 

 graduates into it in an imperceptible manner. As 

 might be expected, it alternates with the primary 

 limestones, since these occur in every situation among 

 the primary strata. I know not that extensive masses 

 of this rock have yet been found succeeding to equally 

 extensive ones of the argillaceous schists, and in con- 

 tact ; but, in Isla, considerable bodies of the latter are 

 found beneath the micaceous schist, though separated 

 from it by intervening beds of quartz rock. Lastly, 

 as a deposit independent of other rocks, or only par- 

 tially intermingled with them, it is intimately asso- 

 ciated with chlorite schist, and occasionally with 

 talcose schist, as will immediately appear. 



Besides these connexions on the great scale, it is 

 associated with many different substances, in smaller 

 quantity and in frequent alternations. In the chain 

 of Isla, it thus alternates, in repeated beds, with quartz 

 rock, clay-slate, and graywacke of various characters ; 

 these alternations being extremely numerous, arid the 

 space occupied by the micaceous schist often very 

 minute, as again noticed under Argillaceous schist ; 

 and it will be seen, under Chlorite schist, that it thus 

 also enters into another series of which that rock 

 and hornblende schist form the most remarkable por- 

 tions. From this history of its alternations, mav be 



