EELATION TO MESOZOIC ROCKS IN THE LEPONTINE ALPS. 197 



doubtful whether the phyllite which occurs at Altkirch, and pre- 

 sumably those pierced by the St. Gothard tunnel, of which the 

 northernmost at any rate may be safely identified with the former 

 rock, are of Jurassic age. The Swiss geologists consider (rightly, as 

 I believe) the phyllites south of the " sericite gneiss " (above the 

 village of Andermatt) to be members of the Carboniferous group, 

 as also an infolded strip which crosses the Lukmanier road at 

 Curaglia. Other like infolds occur (according to the older authori- 

 ties, who, I believe, are correct) in the valley of the Ehone, as, for 

 instance, at the north base of theSimplon Pass and elsewhere in the 

 neighbourhood of Brieg; and a narrow strip of the same rock, in my 

 opinion, is cut through by the Binnenthal, to the north of the great 

 mass of dark cr3stalline schists, from which it is macroscopically 

 not easily distinguished *. I am, of course, aware that in a case of 

 this kind it is hazardous to rely on lithological resemblances, but it 

 is at any rate remarkable that there is not only a strong family like- 

 ness, in such Alpine rocks as I have examined, among the phyllites 

 of Carboniferous age on the one hand and those of Jurassic age on 

 the other, but also a distinction between the two groups, due, as I 

 believe, to an original difference in the materials, the former having 

 been more directly derived from the older crystalline rocks. If this 

 identification of the Altkirch phyllite be correct, the relation of the 

 crystalline series, the Carboniferous phyllites, and the Jurassic rocks 

 of the upper Eeuss valley would very closely resemble that which 

 I have already described, and which is universally admitted, in the 

 valley of the Ilomanche t. 



Be this as it may, whether the Altkirch phyllite be Carboniferous 

 or Jurassic in age, if we place it in the same group with this marble 

 and calc-mica schist, the section presents us with the following 

 difiiculties. The argillaceous members of a consecutive sequence 

 are comparatively unaltered, while the calcareous are intensely 

 metamorphosed ; for in them not only have the calcareous consti- 

 tuents become completely crystalline, but also the argillaceous have 

 been converted into flakes of mica of considerable size — a result of 

 environment which is hardly in accordance with the general teaching 

 of nature. Again, both rocks have been affected, though, as is 

 usually the case in associated strata of unlike composition, to a 

 different extent, by pressure. This has produced the usual effect 

 upon the clay by converting it into a phyllite ; but it has first of all 

 (according to the hypothesis) converted the calcareous rock into 

 crystalline limestone and banded calc-mica schist, and has then im- 

 printed upon it the usual mark of dynamic change. Purther, the 

 section appears to prove too much for the advocates of theories of 

 *•' pressure metamorphism," for the transition between the phyllites 



* I twice walked over this strip without observing the distinction, but detected 

 it on a third occasion, as the occurrence of fragments of a dark schistose rock 

 in the adjacent rauchwacke led to a more careful examination of the underlying 

 rock. The similarity is probably due to the " anthracit-schiefer " having been 

 hirgely composed of fragmental mica, iind liaving derived locally much of its 

 material from the adjacent dark schit«t. 



t Quart. Journ. Geol. Soc. vol. xlv. p. 73. 



