— 87 -- 



terisUc slriicliires. Wo fiinl (tnly the staleinenl : lli;il it difters from 

 the ordinary giieiss in Ihe norlhern [tarl of Ihe Finsleraarmassif in 

 its conspicuoiis «M ö r t e 1 s l r ii c t u r» (for the description of whicli 

 rereroiice is made lo a foreigii wriler) in Ihe defornialion of the 

 feldspars and llie prodiiclion of soricite froni Ihem.» 



Bonney fährt fort nach Anführung des Passns : Inwiefern gerade 

 diese Mörlelstnicliir clc. (siehe oben bei Baltzer) «I have been for 

 some years familiär wilh Greywackes which have been Ihiis modilied, 

 and as aniple niaterial for study could be oblained'wilhout going beyond 

 Ihe Hniits of the Al|)s, I niust beg leave to dispute the accuracy 

 of this remark.» Bonney führt nun die verschiedenen Verände- 

 rungen, denen (lesteine durch Dynanionietaniorphismus ;inler\vorfen 

 werden können . an und beschreibt die verschiedenen 

 G n e i s s V a r i e t ä l n der Umgebung von G u 1 1 a n n e n 

 und kommt zu dem Schhiss : «Tliat the G a r b o n i f c r o u s g n e i s s 

 is more variabh^ and holerogeneous. It presents the aspect of a r o c k 

 c m p s e d o f f r a g m e n t s d e r i v e d f i- o m s 1 i g l li 1 y 

 d i f f e r e n t s o u r c e s ; the o t h e r t h a t o f a rock 1 o c a 1 1 y 

 c r u s h e d t o f r a g m e n t s. 'J The distinclion is very marked in 

 the specimens identified as Gneiss in or ch)se to the infold of Garboni- 

 ferous Rock: for instance in that of Vorsaas.» Und weiter: 



«To sum ui): my study of the Guitannen rocks both in the lieid 

 and wilh the microscope leads nie to the following conclusion : 



« As in the case whith other rocks of Carboniferous age else- 

 where in tiie Alps, they are comi)osed exclusively, or ahnest so, of the 

 debris of the crystaliine rocks of the neighbourhood, they often, Hke 

 the T o r r i d n S a n d s t o n o in S c o 1 1 a n d or the G i" e s f e 1 d - 

 s p a t i q u e o f N o r in a n d y , are in i n e r a 1 o g i c a 1 1 y idenlical 

 with a granile on a granilical gneiss, and occasionaily cannot be dis- 

 tinguished even sti'ucluraliy etc. etc. » Und weiter : «So if we are prepared 

 to call the Torridon Sands tone a granite and the Gres 

 f e 1 d s p a l h i (j u e a gneiss, simply because here and there it 

 would be difficult lo i)oinl out a distinclion which would ap[)ear al 

 once lo an inexperienced eye -simply because they are rather clever 

 imitalions — Ihen we inay call the Guttannen rock a gneiss, 

 bul in thal case we may as well adinit frankly that pelrology is a 

 hopeless muddle, and that any atlempl lo invesligale the hisiory of 



*) Vom Referenten ycspeni. 



