268 MICACEOUS SCHIST. 



The individual strata in a series, are equally 

 variable in dimensions, but are most commonly 

 very thick where that series contains no inter- 

 vening substance. They are often indeed of a 

 thickness so great, and are, at the same time so 

 imperfectly defined or separated, that the stratified 

 nature of the rock is only to be deduced from a 

 knowledge of its general characters, and not 

 from any appearances visible in the spot under 

 examination. The difficulty of determining this 

 point is greatest, as in gneiss, where the disposi- 

 tion of the beds is least regular, or where they 

 are much bent or contorted. 



When the beds of micaceous schist are not 

 separated by any intervening rock, they are dis- 

 tinguished, like those of gneiss, by some change 

 in the proportions of the constituent parts, and 

 the actual separation takes place where the mica 

 is most abundant. 



The flexures above-mentioned as occurring 

 in this rock, are often so great as to amount to 

 contortions. But in many cases of contortion, 

 where the intricacy and minuteness of this struc- 

 ture is very considerable, this feature appears to 



