236 PEOP. T. G. BONNEY ON CRYSTALLINE SCHISTS AND THEIR 



I admit that the evidence of this specimen is not such as would 

 convince an ordinary observer, but after long familiarity with 

 schists and derivative rocks, I am unable to come to any other con- 

 clusion than that the garnet, to say nothing of other minerals, has 

 not been developed in situ, but occurs in derivative fragments *. 

 If this be so, no stronger proof could be given of the independence 

 and antiquity of the Piora-schist group — and this, coupled with 

 that already obtained from the rauchwacke, if admitted, places the 

 matter beyond dispute. This instance is only one out of many 

 which indicate (as I have already more than once observed) that 

 there had been " mountain-making " in the region of the present 

 Alpine chain before any Mesozoic rock was deposited, and even in 

 Pre-Carboniferous times. 



Discussion. 



Dr. Geikie stated that he had sent an abstract of the paper by 

 Prof. Bonneyt, read to the British Association at Newcastle, to Prof. 

 Heim, and the latter had favoured him with a resume of his views 

 on the subject of the present discussion, of which the following is a 

 translation : — 



" It appears to me that Professor Bonney starts from a misunderstanding. It 

 has often been maintained that Mesozoic rocks can become crystalline ; but no 

 Swiss geologist has, so far as I know, ever asserted that the crystalline schists of 

 the Central massif of the Alps are raetaraorphic Mesozoic rocks. In the printed 

 abstract of his British-Association paper, however, which you have sent to me, 

 Professor Bonney attacks this suppo3ed assertion — one that has never been 

 made. 



"I am in perfect accordance with those who know the Central massif best 

 (Baltzer, Fellenberg, &c.) in iixing the following points : — 



"1. Crystalline schistose rocks of Mesozoic age exist at Scopi, in the Valserthal 

 (Graubiinden), in the Urserenthal, on Piora, at the Nufenen Pass, in the Val 

 Canaria, in the Ganterthal, and numerous other places. Such rocks are : — 



" (a) Clay-slates, with mica, garnets, zoisite, staurolite, rutile, and Belemnites, 

 the latter being crystalline and granular. 



" (b) Clay-slates, with mica, staurolite, &c., and garnet, alternating with the 

 Belemnite-schists. 



" {c) Green plagioclase-amphibole schists, alternating with the Belemnite- 

 schists. 



" (d) Micaceous phyllites and calcareous mica-schists. 



" (e) Marble with mica, which has undergone linear stretching, going ovei- 

 into ' Malm-kalk ' with crinoids. 



" 2. We have never given the name ' crystalline-schists' to these rocks, nor 

 have we ever regarded them as such, but always as sedimentary metamorphosed 

 zones (synclinal basins) between the central massifs. Professor Bonney is right 

 in saying that they liave not the aspect of true crystalline schists. It is true 

 there are some varieties which it would be difficult to distinguish in the hand- 

 specitiien, and without stratigraphical evidence, from true crystalline schists. 

 Stratigraphically, they always present themselves as ' Mulden-zones ' accom- 

 panied by other sedimentary rocks. 



* My specimen of the Black-garnet schists collected between the top of the 

 Lukmanier Pass and Somascona (President's Address, 1886, Q. J. G. S. vol. xlii., 

 Proo. p. 47) in parts very closely resembles the fragment here described. The 

 rock has evidently been much affected by pressure. 



'■ Prof. Bonney states that the printed document sent to Prof. Heim con- 

 tained the whole of the note communicated by him to the British Association. 



