557 



SILICEOUS SCHIST. 



THE difficulty of procuring accurate informa- 

 tion respecting the geological connections of this 

 rock, in the works of foreign authors, and the 

 obvious errors that have followed, from confound- 

 ing it with the quartzose argillaceous schists, com- 

 pd me to limit the following remarks to my own 

 observations. 



The reasons for placing it in this division 

 require no further explanation than that already 

 given in the two preceding chapters. 



In the primary class, it occurs in the same 



situations as the ordinary argillaceous schist to 



which it is so nearly allied, and it also passes into 



that rock by imperceptible gradation. Hence its 



characters vary, not only according to the degree 



of its induration, or the perfection of its structure, 



.but according to the peculiar quality of the strata 



with which it is connected. Like jasper, it will 



