12 Br. F. M. Stapff— Crystalline Schists 



Geol. Durchschnitte, Siidseite, is highly instructive for the inter- 

 pretation of the rather irregular or lenticular masses of rauchwacke 

 which figure on the geological maps of the country. The same 

 rock which, in the ragged cliffs N.E. and S.V/. of the tunnel, 

 appears almost homogeneous (though greatly decayed), is, in the 

 tunnel, unrolled in a long series of alternating concordant strata of 

 rauchwacke, saccharoidal dolomite, marble, breccia, ' ash,'' quartzite, 

 and mica schist, this last named forming not only some well-defined 

 beds at the end of the series, but also thin separating sheets between 

 the different calcareous layers, and patches in their mass. I am 

 not convinced that these fragments are, in all cases, the detritus of 

 pre-existing mica schist inclosed in the lime rock ; sometimes the 

 white, gray, or greenish coatings of talcose mica appear to have 

 been formed contemporaneously with the calcareous material or even 

 subsequently ; in other instances they are certainly torn and crushed 

 fragments of the intercalated mica schist which have been squeezed 

 into the dolomite by mechanical forces. Prof. Bonney lays stress 

 upon the occurrence in the dolomites, etc., of fragments of mica 

 schist, which indicate their psammitlc nature. With the reservation 

 just mentioned, I share this view, which I have already published 

 in the " Geol. Durchschnitte und Tabellen, Siidseite," specially with 

 reference to No. 10 ("dolomitic ash," a dirty greenish medley of 

 dolomite, talc, etc.) and to No. 14 ("breccia" at 78'5m., which is 

 thus described, " Yellowish, ashy, cavernous rauchwacke, inclosing 

 sharp-edged fragments of talcose mica schist and of saccharoidal 

 dolomite, with white or rusty saccharoidal or sandy dolomite in the 

 cavities. This bed, so far as it is not a vein, proves that the 

 dolomitic strata are younger than the mica schist on their hanging 

 wall "). Very similar remarks are made in the text to the Geological 

 profile (German, p. 44; French, p. 48, and in "Verhandl. der 

 Schweiz. Naturf. Gesellsch." 1874-75, p. 139) : "the occurrence of 

 this mica-dolomite breccia seems to prove that the dolomites are 

 younger than the surrounding mica schists." 



Dolomitic material is predominant in the chequered line of thin 

 strata in this section of the tunnel, which have together been sub- 

 jected in common to contortion, faulting and squeezing, so that it 

 is difficult to understand why the same mechanical forces should 

 not have exercised similar metamorphic effects on every individual 

 bed of the whole series, which they are believed to have exercised on 

 some of them ; why, for example, mechanical " marmorization " has 

 taken place in No. 17 at 82-3 — 83 m. ; but not in the preceding bed 

 of white loose saccharoidal dolomite, nor in the following one of 

 white and red dolomitic bands which alternate with strings of 

 quartz and mica-schist? How are we to explain the alternation of 

 beds of rauchwacke with saccharoidal limestone if the transformation 

 of one of these substances into the other were due to pressure which 

 has acted through the whole complex ? Leaving on one side the 

 formation of breccias, it does not seem probable that petrographic 

 metamorphosis by mechanical forces has played an important role 

 in our case ; I am inclined to consider that the chemical or physical 



