OF CAEBONIFEROFS AGE AT GFTTANNEN'. 399 



rock a gneiss, but in that case we may as well admit frankly that 

 petrology is a hopeless muddle, and that any attempt to investigate 

 the history of the schists and gneisses is a waste of time ; or in 

 other words — for I do not see where we are to stop in applying the 

 principle — that the banker or the archaeologist is at the mercy of the 

 accomplished forger. 



Discussiois'. 



The President observed that this, an old controversy, was likely 

 to remain one for some time to come. JFirstly, it was necessary to 

 define a gneiss, and such definition must be based entirely on petro- 

 graphical characters. In the case described by the Author, we have 

 a rock which is clearly detrital (containing as it does recognizable 

 fossils), and this exhibits a structure to a certain extent gneissic, 

 though he presumed that the Author would deny that it was a 

 gneiss ; but supposing that alteration had gone on a step farther, 

 and nearly all trace of organic structure was gone, he (the speaker) 

 thought that the gneissic structure would increase in intensity, so 

 that it could not be distinguished from what he supposed the Author 

 would admit to be a normal gneiss. He considered that an argu- 

 ment used by the Author, as to its being extraordinary that fossil 

 plants were preserved in true gneiss, cut both ways. If a detrital 

 rock be chemically and mineralogically allied to a gneiss, then, on 

 the occurrence of further change, one can only say that the rock is 

 a gneiss, without defining what sort of a gneiss it is. 



Prof. JuBD congratulated the Author of the paper on having so 

 satisfactorily disposed of an erroneous observation. Por himself, he 

 had always doubted cases of the alleged occurrence of fossils in holo- 

 crystalline rocks. If the rocks are holocrystalline, how could original 

 structures like fossils be preserved ? If, on the other hand, the 

 rock did preserve the structure of a fossil, how could it be said to have 

 been perfectly recrystallized ? He thought the doctrine of dynamo- 

 metamorphism (and we must remember that the doctrine is much 

 older than the name it now bears) had suffered from trop cle zele on 

 the part of some of its supporters. He regarded many of the observa- 

 tions of Prof. Bonney, even in the present paper, as affording valuable 

 support to the doctrine of dynamo-metamorphism. 



Mr. EccLES fully believed in the Carboniferous age of these 

 ' Sericite Schists ' at Guttannen, and considered them to belong to 

 a prolongation of one and the same infold, which includes fossili- 

 ferous strata of the same age in the massif of the Todi to the 

 N.E., as well as those of the Lower Yalais to the S.W., all the three 

 occurrences being approximately on the same strike-line. But he 

 was not prepared to admit that Carboniferous strata, altered or un- 

 altered, entered in any considerable degree into the composition of 

 the crystalline zone which extends from the Todi to Dauphine', and 

 of which these Guttannen schists form a part. In support of this 

 contention he pointed out that all the known Carboniferous expo- 

 sures in this zone except one, which may not after all be an ex- 

 ception, are synclinals of comparatively limited width sharply in- 



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