350 ARGILLACEOUS SCHIST. 



tain prtiof of this is, in some instances, afforded 

 by the persistence of the fissile tendency, or the 

 lines of splitting, through beds which, in differ- 

 ent places, present an alternating fine and coarse 

 texture indicating the true position of the stratum, 

 or that in which the deposition of the materials 

 took place. 



As the seams, or divisions of the strata of ar^ 

 gillaceous schist, are often invisible, either in 

 consequence of their great distance from each 

 other, or from the nature of the ground, or from 

 other causes, the fissile direction may often be 

 mistaken for the plane of the stratification. The 

 alternation of the fine and coarse kinds, here serves 

 to mark the true disposition of the bed, even 

 where the different textures are not actually di- 

 vided ; but where neither of these indications are 

 present, there seems to be no criterion by which 

 the one can be distinguished from the other. 



This doubt is necessarily confirmed by the 



jact, that, it* many instances, the fissile tendency 



is actually parallel to the plane of stratification, 



as it invariably appears to be in the secondary 



argillaceous schists or slates. In these cases it 



