184 



CHAP. XXX. 



Argillaceous Schist. 



As the present title includes all the primary varieties 

 of this rock, it comprises the Clay-slate and the Gray- 

 wacke of Geologists ; excluding all the similar sub- 

 stances in the secondary class, under the term Shale- 

 The distinction is a geological, not a mineral one ; and 

 the present arrangement, or innovation, has long been 

 needed: since the confusion originally produced by 

 the Germans, and continued by their followers, in ad- 

 opting and misapplying the term Graywacke, has ren- 

 dered their writings worse than useless. This division 

 of the primary schists appears to have been first founded 

 on erroneous observation, as it has been continued by 

 those who find it easier to follow authority than to 

 observe. 



It was never, indeed, very easy to learn the opinions 

 of Werner ; yet he appears to have mistaken the red 

 marl for the lowest sandstone, thus erroneously assign- 

 ing to it the first place among the secondary strata. 

 Hence, confusion was first introduced into his views 

 of these, while the mountain limestone and the old 

 red sandstone became excluded, and placed either in 

 his transition, or in the primary, series. 



Now as this sandstone series often contains as much, 

 or more of argillaceous schists, than it does of sandstones, 

 and as many of these are formed of fragments, being, 

 in a mineralogical sense, coarse graywacke, it appears 

 to have laid the foundation both of his graywacke and 

 his transition ; while it is easy to see how exactly it 

 tallies with all the characters which he has given, as 

 it occurs with us. The remainder of the confusion 

 follows of course. They who were guided by words 



