164 Professor T. G. Bonneij — Schists in Lopontine Alps. 



have been affected by pressure, but they were crystalline scbists 

 before that acted, for the larger minerals are sometimes distorted 

 or even crushed, the garnets in one or two localities being distinctly 

 cleaved. Pressure, in fact, has injured more than it has originated 

 the crystalline condition. But the Jurassic rocks are only schistose ; 

 they have been affected by pressure, and it has produced the usual 

 mineral changes on a comparatively small scale. But besides this, 

 in some localities a number of ovoid and of rudely prismatic bodies 

 have formed (the Tcnoten and prismen of Von Fritsch), These, which 

 occur along with fossils (belemnites, bits of crinoids, etc.), are not 

 either garnets or staurolites, but only very impure silicates, more or 

 less hydrous ; some probably belong to the chloritoid, others perhaps 

 to the scapolite group, with possibly a third mineral of the same 

 general character.^ Professor Heim asks almost in a tone of triumph ^ 

 whether I have not seen " die Verquetschungen und die Veriinderung 

 (Marmorisirung) in der Structur der Belemniten .... die 

 ganz mit der Umiinderung des Muttergesteines parallel geht." 

 Certainly I have : indeed have mentioned it (loc. cit., p. 219). But 

 by this question he shows that he can have given very little time to 

 the study of metamorphism. Otherwise he would have known that 

 this ' marmorosis,' notwithstanding its fine name, proves but little, 

 for calcite is one of those minerals which are always ready to 

 crystallize, and particularly so when it is ' organic' We constantly 

 see this illustrated in rocks (especially Paleeozoic) from English 

 localities. There are no signs of pressure, yet fragments of 

 fossils may be often found under the microscope to become partially 

 or even wholly crystalline, to the obliteration of the original 

 structure. I have also seen tests or spines of echinids from the 

 Chalk break as if they were crystalline calcite, and a fractured 

 stalactite showing the cleavage surface of large crystals.^ Professor 

 Heim, however, seeks to minimize my criticisms by intimating 

 that I am a prejudiced witness, and have from the first shown 

 signs of a distinct bias (tendenz). Of this I am convicted by 

 my own confession, because I stated that, when I saw the 

 specimens on which he rested his case, and which he exhibited at 

 Burlington House in 1888, " ' Still, I was not quite satisfied 

 . for it was very difficult to understand how such a fossil 

 as a belemnite could have retained its characteristic form while 



' Dr. Schmidt admits the presence of clintouite (which name is now appHed by 

 Dana to the group inchiding the species of chloritoid), and assigns the knoten and 

 piismen to zoisite. Both minerals are so full of impurities that it is veiy difficult to 

 come to any conclusion, but neither reminds me of zoisites, nor is any close relationship 

 suggested by the analyses (quoted on p. 233 of my paper) ; and after reconsideration 

 of my specimens I see no reason to change what I wrote in 1890 (Quart. Jouru. Geol. 

 Soc, vol. xlvi, pp. 232-234). Dr. Schmidt's petrographical description will be 

 found in Beitrage, vol. xxv, Anhang, pp. 41-65. 



- Beitrage, ut supra, p. 317- 



^ Though I think that, as a rule, I can distinguish a marble belonging to a group 

 of crystalline schists from an ordinary Palaeozoic or later limestone, even if 

 pressure modified, I put more reliance on any sOicates which may be associated with 

 the calcite, and do not feel quite happy unless I can trace the rock into some schist 

 composed largely of these. 



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