EELATION" TO MESOZOIC ROOKS IN THE LEPONTINE ALPS. 21 i) 



weathering : moreover the best specimens have a trick of occurring* 

 towards the middle of the iiattish surface of a block, which may be 

 about 16 square feet in area and a yard or so thick ! These blocks 

 are frequently very distinctly banded, layers of a grey calcareous 

 mudstone alternating with dark layers full of rounded and prismatic 

 spots : these minerals are rare and small in the former, but fossils 

 occur in both. The " spotted " bands pass rapidly into the compact 

 rock, and are sometimes split up by it, as when a grit is associated 

 with a shale. The mineral " spots " are rather indistinct on a fresh- 

 broken surface, but are very clearly displayed on a weathered one by 

 projecting from the matrix. One block exhibited an interbanding 

 of a fine-grained, hard mudstone and coarse micaceous layers, 

 commonly two or three inches thick, curiously twisted, evidently by 

 subsequent pressure. The rock, as a whole, has been subjected to 

 considerable pressure and generally exhibits a rough imperfect 

 cleavage, which is usually parallel with the bedding, but can occa- 

 sionally be seen to cross the latter at a fairly high angle. Another 

 peculiarity should be noticed. This rock in weathering breaks up 

 — sometimes with considerable facility — into rude flakes — as it were 

 *' scaling " off — as is common with rather coarse mudstones in 

 which a cleavage or bedding may be traced. This characteristic is 

 very conspicuous just at the top of the pass * (where the rock is in 

 situ). Here it reminded me of certain hard, gritty. Carboniferous 

 shales, and it gives to the scenery a curiously dull, dirty, and 

 generally untidy aspect. In this respect it differs markedly from 

 the habit of the black-garnet schist. The unpropitious state of the 

 weather prevented us from, ascending the Nufenenstock to examine 

 the section at its summit, or from devoting much time to a search 

 for any true Black-garnet schist, and an examination of the rauch- 

 wacke to the north of the pass f. There is not, however, space for 

 much of either, for the gneiss crops out abundantly at a very short 

 distance to the north. Eauchwacko, however, is there, but most of 

 it occurs as detached blocks. One of these contained pieces of a 

 satiny schist like the " Distheue " schist of the Yal Canaria. There 

 must also be a remnant (as at the Alp Vitgira) of the Elack-garnet 

 schist, for we found a few loose blocks, in one of which the garnets 

 were of a dark red colour. 



If the rock on the top of the I^ufenenstock is identical with that 

 on the pass itself, as, from what I saw at the entrance of the Val 

 Corno, I presume it is, the Jurassic rock may form a true trough, 

 though it must rest upon rather than be intercalated in the Piora 

 series as a whole. For on the north side of the pass there is 

 certainly gneiss with at most a mere scrap of the Black-garnet 



* A hard sandstone is interbanded in the scries close to the top of the pass, 

 the bands dipping roughly south at an angle of at least 70°, 



t Perhaps I should state that this did not interfere with our examination of 

 the eastern side. We were able to satisfy ourselves thoroughly as to the great 

 mass of the fossiliferous and spotted rock, but just when we had completed the 

 examination of this, a dull morning changed to heavy rain, and obliged us to 

 hurry down into the Eginenthal without minutely examining the short space 

 between the " spotted rock " and the gneiss, or climbing the Nufeueustock. 



