344 



ARGILLACEOUS SCHIST, 



UJSDER this head are included all the schistose 

 argillaceous rocks of the primary class, however 

 differing in texture, and it thus comprises the 

 clay slate and the gray wacke of some geologists. 

 The reasons for adopting this innovation are the 

 following. 



In all cases, the coarser and finer varieties of 

 this rock occur as parts of one series, however the 

 one or the other variety may predominate in par- 

 ticular instances. If ever fine beds, or strata of 

 clay slate, are found unaccompanied by coarser, 

 or if the coarser are occasionally seen excluding 

 the finer, these instances are insufficient to jus- 

 tify a separation of the two, any more than the 

 separation of gneiss or of micaceous schist of 

 coarse and fine textures would be justified by si- 

 milar circumstances. Moreover, even the same 

 bed will sometimes present both textures ; the 



