of the Cornish Rocks. 105 



extended by later geologists, through all the regular grada- 

 tions observable in the grain of the mass, to argillaceous slate, 

 which has never been suspected of being derivative ; and after 

 an unavailing attempt to maintain the line of distinction be- 

 tween these two rock-formations, by some external characters, 

 which are not sufficiently constant to be of any importance, it 

 is now pretty generally acknowledged that the terms grey- 

 wacke slate and argillaceous slate are convertible, it being im- 

 possible, without the aid of petrifactions, to ascertain where the 

 one ends and the other begins. 



A dilemma so unfortunate as this is, ought to liave sug- 

 gested the jirobability of some error in the process of reason- 

 ing upon which these distinctions are founded, and might have 

 sooner led to its correction ; for, as the priority of formation 

 was confessedly due to that slate which contained no petrifac- 

 tions, it was natural to conclude that the order of transition, 

 if there w ere any, would be conformable with the march of 

 nature. It is surprising, as the derivative origin of the grey- 

 wiicke rests so much upon diis view of the subject, that there 

 should ever have been any other opinion in respect to this or- 

 der, and that the grey-wacke rock, instead of terminating the for- 

 mation of argillaceous slate, should have been regarded as its 

 archetype, or tire point from which it proceeded. So general, 

 nevertheless, has been this misconception, that the terms grey- 

 wacke and grey-wacke slate have been applied, without re- 

 serve, to strata which exhibit in a very imperfect manner, if 

 at all, the derivative character, and which are altogether de- 

 stitute either of petrifactions or of the limestone beds containing 

 them ; — in short, to a primitive rock, in no respect whatever 

 differing from our argillaceous slate: the consequence of which 

 is, that this latter and more ancient denomination is now, in 

 the literal sense of the word, losing ground, and gradually bcx 

 coming obsolete. 



It does not appear that Werner had ever contem]ilated this 

 abuse of a denomination, which the progress of discovery, at 

 the period when lie first adopted it, seemed in his oj)inion to 

 justify. Struck with the derivative nature of this rock, and 

 the organic remains which were occasionally observed in the 

 mass, he found it expedient to separate it in his earliest syste- 

 matical arrangement, even from the argillaceous sbile into 

 which he had traced its transition, antl with which it alter- 

 nated. Accordingly, in the short or elementary classification 

 of mountain rocks (gebirgs-arlcn) which he published in the 

 year 1787, the grey-wacke is placed among the derivative 

 rocks at the head of the secondary class but no mention is 



Vol. 61. No. 293. /'c/;. 1823. ' O made 



