OP CARBONIFEKOUS AGE AT GUTTANNEX. 395 



being retained, witli some indications of the intervening material, 

 much as may be often seen in a sandstone from the Carboniferous 

 system. But if the molecular changes among the constituents 

 have been sufficient to transform a shale or a grit into a gneiss, is 

 it not strange that anything more than a mere trace of the plant 

 should be preserved ? I do not say that the difficulty is insuperable, 

 but it exists, and ought, it appears to me, to have been careftdly 

 discussed. Yet ^ve do not find a word on the subject. The occur- 

 rence of a fairly well-preserved fossil in a rock which has passed 

 into a crystalline condition seems to be regarded as a thing per- 

 fectly normal and natural.^ 



Here is the second point. We might have expected ample evidence 

 that the rock of the Guttannen boulder had been carefully compared 

 with numerous specimens of gneisses and crystalline schists from 

 other parts of the Alps, at least, in order to show that it agreed 

 completely with them in its characteristic structures. We find only 

 this statement : that it differs from the ordinary gneiss of the 

 northern part of the Finsteraar massif in its conspicuous ' Moy^tel- 

 structur ' (for the description of which reference is made to a 

 foreign writer), in the deformation of the felspars, and the pro- 

 duction of sericite from them. This statement ends with a remark- 

 able clause: — "Inwiefern gerade diese Mortelstructur auf einen 

 klastischen Ilrsprang des Gresteines hinweist, kann nicht mit 

 Bestimmtheit entschieden werden, da die Wirkungen der Dynamo- 

 metamorphose auf Grauwacken noch zu wenig bekannt sind." As 

 I have been for some years familiar with greywackes which have 

 been thus modified, and as ample material for study could be 

 obtained without going beyond the limits of the Alps, I must beg 

 leave to dispute the accuracy of this remark. 



The Alps provide an abundant series of rocks illustrative of the 

 various stages of pressure-metamorphism. Restricting ourselves on 

 the present occasion to a single group only, we can readily obtain 

 a series at one end of which is an almost normal granite or granitoid 

 gneiss, at the other a fine-grained quartzose or micaceous schist. 

 We can study under the microscope the gradual detrition and change 

 of the original constituents — the crumpling, tearing, and partial 

 reconstitution of the micas, the cracking and crushing up of the 

 quartzes, the progressive pulverization of the felspar and its re- 

 placement by filmy ' sericite ' and chalcedonic quartz. With such 

 specimens, of which I possess a large series (not a few from the 

 Central massif)^ these ' Carboniferous gneisses ' can be compared, on 

 the one hand, and on the other with greywackes composed of the 

 debris of crystalline rocks which have been subsequently subjected 



^ It may be said, ' But this is not regarded as a gneiss in the sense in which 

 the term is applied to the rock farther down the valley.' If it be not — if the 

 rock be only a shghtly modified grit, looking like a gueiss—theve is of com-se an 

 end of the matter. But if so, whei'e is the importance of the discovery, what 

 bearing had it on the questions discussed in my paper ' On the Crystalline 

 Schists, &c.,' and why import confusion of thought into a perfectly simple 

 matter by the emploj'ment of a misleading terminology ? 



