RELATION TO MESOZOIC ROCKS IN THE LEPONTINE ALPS. 211 



illusory, — and that the latter really overlies and is much later in date 

 than the former. 



The evidence in this locality appears to me decisive, and it is of 

 a kind which would render it needless to pursue the investigatiou 

 further ; for the schists of the Piora group are so different from those 

 of the Tremola group that there is little danger of confusion between 

 a member of the former and one of the latter. Still it may be well 

 to add that the above case is by no means an isolated one. For 

 instance, near the top of the Nufenen Pass, as will presently be de- 

 scribed, some rauchwacke occurs. This also contains fragments of a 

 satiny mica-schist, resembling the so-called disthene-schist mentioned 

 above. Again, in the lower part of the Binnenthal, the path to the 

 village of Binn crosses some rauchwacke at the mouth of a ravine 

 cut deeply into a mass of dark schists whicli can be traced up the 

 valley above Binn, and ultimately passes eastward by the flank of the 

 Ofenhorn to the Gries Pass, the neighbourhood of the Nufenen Pass, 

 and the Val Bredretto. These schists are dark-coloured mica-schists, 

 sometimes rather calcareous. In their lower part they include a 

 mass of crystalline dolomite *, and the peculiar black-garnet schist 

 occurs in the bed of the river a short distance above Binn f. The 

 connexion of these schists with the Piora group cannot be doubted ; 

 both form part of the same great series which, as I have already 

 said, can be traced from one end of the Alps to the other. Hence 

 they ought, if the hypothesis which we are discussing be correct, to 

 be more modern than the rauchwacke. But this contains fragments 

 of a rock which has a remarkable resemblance to these schists. 



One objection might, however, be made. These fragments arc 

 neither numerous nor large, and it is uncertain whether they repre- 

 sent the true Binn schists. While there can be no doubt as to the 

 nature of the rock through which the greater part of the ravine is 

 cut, there is some difficulty at the opening. A short distance higher 

 up there arc some indications of another bed of rauchwacke, and the 

 rock, which south of this is an undoubted schist, suddenly assumes 

 a more slaty character, and it is difficult to determine whether we 

 have found the schist in a very crushed condition or a true slate. 

 Such a rock in this part of the lihonc valley (as, for instance, near 

 the foot of the Simplon Pass) is often found in contiguity with the 

 schist and bears some resemblance to it (being probably largely 

 derived from it), and might very well occur just in this position. 

 After careful study of slides cut from two rather typical specimens 

 collected in the neighbourhood of the rauchwacke, I incline to 

 regard this rock as only a pliyllite, not a true schist. Be this as 

 it may, the same rock indubitably occurs as a fragment in the 

 adjacent rauchwacke. This, however, contains other smaller frag- 

 ments more closely resembling schists, besides mica corresponding 



* A white saccharoidal rock resemWing the marbles whicli elsewhere occur 

 interbeclded with schists and totally unlike any rock 1 have seen in the rauch- 

 wacke group. 



t It was detected by Mr. Eccles as we were returning from an ascent of the 

 Ofenhorn. 



