OP CAKB0NIFER0U8 AGE AT GUTTANNEN-. 397 



on which a rude cleavage has been subsequently impressed. Traces 

 of a like structure can also be distinctly recognized in the rock with 

 white spots, already mentioned as occurring at the above-named 

 locality. These spots are felspar; they bear no resemblance to 

 authigenous minerals, though the outline of the fragment in places 

 is a little obscured by the formation of a narrow zone of chalcedonic 

 quartz, calcite (?), and other secondary products. The specimen 

 from the crag which rises by the path on the left bank of the Aar 

 consists of rather coarser detritus than the last-named example, 

 that is, of the debris of a normal granitoid rock. 



The crystalline rocks of the Haslithal above and below Guttann en, 

 already briefly mentioned, must now receive a little further notice. 

 On the Swiss map, those north of the ' Carboniferous gneiss ' are 

 coloured as gneiss : those south of it (with an unimportant exception) 

 as hank-granit, gneiss-granit, aug en-gneiss. The former un- 

 doubtedly are less coarse-grained and granite-like than the latter ; 

 in short, the Haslithal section is generally similar to those obtained 

 in crossing the Oberland range at some few miles distance to th« 

 east or to the west ; the rocks, as we proceed inwards, becoming 

 coarser, more obviously granites rendered gneissoid by pressure, 

 sometimes even porphyritic ; so that for general descriptive purposes 

 the above distinction may be maintained. My collection includes 

 a fair selection of various types of these gneisses or gneissoid 

 granites from the more central part of the Oberland, and I have 

 examined a few from the Haslithal itself. For our present purpose 

 it is needless to enter into minute descriptive details either of 

 structure or constituents. The dominant minerals are quartz, felspar 

 (orthoclase and plagioclase), and mica, commonly biotite. The rocks 

 are sometimes much crushed, when the quartz becomes a mass of 

 variable-sized granules, occasionally almost chalcedonic ; the felspars 

 are partially altered in the usual ways ; the mica flakes are more or 

 less broken up ; but in other cases the modifications are but slight, 

 the felspars sometimes being fairly idiomorphic, though more often, 

 like the quartzes, they are more or less irregular in outline, and 

 contain small grains of the latter mineral. The broad petrographic 

 distinction, mentioned above, is commonly maintained in the slides, 

 those from the upper part of the valley being more like normal 

 granites. Two specimens from above Guttannen contain, it may be 

 noted, small garnets. 



While it is evident that, if we restrict ourselves in a microscopic 

 examination to very small portions of the ' Carboniferous gneiss,' 

 these are identical both in structure and mineral constituents with 

 the above-mentioned gneisses (from which I consider them to have 

 been derived) ; yet, if we examine the slide as a whole, instead of 

 keeping our eyes fixed on what is really a fragment of the true 

 gneiss, we find that the ' Carboniferous gneiss ' is more variable and 

 heterogeneous. It presents the aspect of a rock composed of frag- 

 ments derived from slightly different sources ; the other, that of a 

 rock locally crushed to fragments. The distinction is very marked 

 in the specimens identified as gneiss in or close to the infold of 



Q. J. G. S. No. 191. 2 E 



