166 Professor T. G. Bonney — Schists in Lepontine A/ps. 



I 



garnet, and still more staurolite, are not formed until the materials 

 of the rock have undergone such great molecular changes as to 

 obliterate all traces of a sedimentary origin and convert the rock 

 into a fairly coarse crystalline aggregate of quartz, brown and w^hite 

 mica, andalusite, and other minerals.^ Under such circumstances, 

 I believe that any calcareous organism, if it did not disappear and 

 supply its lime to some silicate, would become unrecognizable. 

 Only in one case, that of the Bastogne rock, have I seen well-formed 

 garnets in a matrix apparently not very greatly altered. These, 

 however, are rather abnormal specimens, and, as it has been latelj^ 

 demonstrated, occur under very abnormal circumstances.- My bias, 

 then, was due to experience, which showed me the antecedent 

 improbability of what Professor Heim was asking me to believe. 



There was yet one other reason for my scepticism. In 1883 

 I crossed the Gries Pass to the Tosa Falls, wishing to see an Alpine 

 route of some historical interest, and with no definite geological aim, 

 for I had but recently begun to make any special study of the 

 'upper schists.'^ Here are some extracts from my diary. Going 

 up the Eginenthal I observed occasionally loose blocks " of a dark 

 slaty or schistose rock, with rounded spots and irregular long 

 darkish crystals, which I took for a kind of ' knoteu schiefer ' and 

 got a specimen."^ Later on I write — "At the head of this [upland 

 basin] there is evidently a great piece of well-bedded rock, not highly 

 metamorphosed, apparently folded in the more crystalline rock. To 

 this apparently the ' knoten schiefer ' belongs, for it was all about 

 here, some of it being rather more schistose than what 1 had seen 

 below." Again, on reaching the top of the pass, I record the presence 

 of dark mica schist with garnets, "looking more highly altered than 

 that below." From the Tosa Falls I crossed to the Binnenthal aud 

 studied the crystalline schists in that district.^ Thus I was aware 

 that in the Lepontine Alps two rocks existed in which some 

 superficial resemblances were associated with real and important 

 differences. In other words, I knew that Nature had been laying 

 traps, so that exceptional caution was needed. 



1 think, then, I may claim that my ' bias ' was the result of 

 knowing certain facts in petrology and Alpine geology better 

 apparently than Professor Heim, and thus was more than justifiable. 

 May 1 ask, in conclusion, that if he thinks he can refute any of the 

 statements in this paper he will abstain from fighting under the 

 shelter of an official publication. There I cannot reply to him ; so 

 the combat is one Ubi tu pulsas, ego vapulo tantum. 



^ Quart. Journ. Geol. Soc, vol. xliv (1888), p. 11. 



- See Miss C. A. Eaisin: Quart. Journ. Geol. Soc, vol. Ivii (1901), p. 55. 

 A museum specimen labelled PjTeneite (from that mountain range) appears to be 

 another instance. 



2 See Quart. Journ. Geol. Soc, vol. xlv (1889), pp. 96-99. 



* This is a transcript of my field notes, in which I do not pick my phi'ases. 

 I probably should not now use the words ' knoten schiefer.' What I meant to 

 express was that it seemed in about the same state of alteration as a chiastolite slate. 



5 A fortnight later I paid my first visit to the Val Piora. 



