Naumann on Primitive Formations, 259 



la BecTie expressed himself, even earlier, in the same manner as 

 Riviere, and doubted whether the metamorphic theory (the sweep- 

 ing hypothesis, as he called it) was admissible in such cases, al- 

 though he quite acknowledges it within its proper limits (Report 

 on the Geology of Cornwall, p. 34). With this, A. Erdmann, a 

 high authority with regard to the Swedish primitive rocks, and 

 Von Blode, who has explored Finland in various directions, per- 

 fectly agree. Von BloJe says : that the raetamorphism is un- 

 deniably present where it can be recognised by observation, and 

 explained generally by physical science. Still the class of rocks 

 with which this is the case, is only limited, and not at all favor, 

 able to the baseless hypothesis which is now being carried to ex- 

 tremes. (Neues Jahrbuch fiir Mineralogie, 1844, s. 53.) Von 

 Leonhard, Petzholdt and others, have also repeatedly declared 

 against the too wide extension of the metamorphic theory, and we 

 are obliged, from complete conviction, to rank ourselves with thera^ 

 The transitions from gneiss, through mica-schist, into crystalline 

 clay-slate are not to be denied, but whether the transitions from 

 crystalline clay-slate into real greywacke slate may pass, in 

 every case, for fully proved, may still be doubted. Griiuer re- 

 marks distinctly that the clay-slate which is associated with gneiss- 

 and mica-schist is always diflferent from the clay-slate of the 

 greywacke; for which reason he declares himself unable to assert 

 that these older rocks, as they appear in the departments of the 

 Rhone and Loire, are metamorphosed greywacke slates. (Ann, 

 des Mines, 3ieme serie, t. 19, 1841, p. 70). 



In our opinion the principal difficulty, and one scarcely to be 

 overcome, lies in the fact that there are far younger gneisses 

 mica-schists, etc., which overlie sedimentary rocks, without the 

 slightest transition into these underlying rocks being observable. 

 In such cases every idea must disappear relative to a hypogenous 

 or anogenous metamorphosis ; for how could the overlying rock 

 have been metamorphosed by some agency from beneath, while 

 the strata beneath remain unaffected by any influence. Just 

 as little can a catogenous metamorphosis be thought of, for what- 

 ever cause one may suppose as the real agency, it is impossible 

 that it can have found in descending, such a sudden and entire 

 check, along one and the same plane of deposition, that the com- 

 pletely re-crystallised rock, should be, by this plane of deposition 

 separated from the perfectly unchanged rock. In such cases 

 there is nothing left for us but the supposition that these strati- 



