214 Pl-COi'. T. G. BONNEY ON CKYSTALLINE SCHISTS AXD THEIK 



its characteristic form while molecular changes of such importance 

 were taking place iu the matrix of the rock. Such inferences as 

 one could draw from the analogy of other cases in Nature seemed to 

 render this one extremely improbable, though of course one could 

 not say impossible *. The more I considered the question, the more 

 I regarded it iu the light of the evidence which I had obtained from 

 my previous studies both in the Alps and in other regions, the 

 greater appeared the difficulties involved in the hypothesis, the 

 stronger the probability of some mistake. 



I have already, I trust, shown that the Elack- garnet schist of the 

 Piora group underlies the rauchwacke, and therefore cannot be 

 identical with these supposed granatiferous rocks of Jurassic age, 

 which it is universally admitted overlie the rauchwacke and, like it, 

 belong to the Mesozoic system. Still we have to consider the 

 possibility that the fossiliferous rock has been converted into a 

 schist undistinguishable from the former. My previous experience 

 made this hypothesis appear very improbable to me, but I thought it 

 ought to be fairly tested. After examining the sections near the 

 Lukmanier and Nufenen passes I deemed it needless to carry my 

 investigations further. 



In describing the results of these I will not begin by giving a 

 detailed description of the supposed garnet-bearing schist iu which 

 fossils occur, but will merely state that the mineral constituents 

 appear either as flattened spheroidal or ovoid grains, about the same 

 size as the garnets, or as somewhat rounded and occasionally rather 

 elongated prisms. Before leaving the subject I shall endeavour to 

 summarize the principal characteristics of these minerals in order to 

 compare them with those of the Elack-garnet schist and its 

 associates. Meantime, in order to avoid prejudging the question, I 

 will refer to the rock in question as " the spotted rock," a trivial 

 name which I think expresses fairly accurately its most marked 

 characteristic. 



(b) The Lulcmanier Pass. 



The upper part of this pass, north of the mass of rauchwacke 

 already mentioned and east of the highroad, is bounded by a 

 mountain -mass of which the southern peak bears the name of Scopi 

 and rises to an elevation of 10,500 feet. On the opposite side of 

 the road is a lower mass called the Alp Vitgira, which, however, is a 

 kind of spur from a group of peaks but little inferior to Scopi in 



* We know that large and well-formed chiastolites are produced by eontact- 

 raetamorphism in a rock (of somewhat similar mineral character) of which the 

 matrix is but little affected. In the Bastogne also garnets of fair size and 

 singularly regular crystalline form have been formed in a matrix but slightly 

 changed. As reference is often made to the latter, I may say that though I 

 have not visited the district, I am familiar (thanks to Messrs. Eenard, Eudler, 

 and Topley) with specimens of the rocks, and am convinced tliat they do not 

 give us much help towards a theory of the formation of o-ystalline schists, as the 

 aarnets are of a very exceptional character. The metamorphism, such as it is, 

 jippears to me due to some unusual agency (certainly not pressui-e). Can it be 

 the passage of hot water? 



