\08 Prof. T. G. Bonney—Metamorphism in an Alpine Rock. 
is not novel, for the Poudingue de Valorsine, as the deposit is called, 
has been noticed by geologists again and again since the days of 
De Saussure, who described it with his usual accuracy; but when 
I state that more than one geologist of importance holds that the 
rock exhibits a considerable amount of metamorphism, I may be 
pardoned for directing attention to it. The Poudingue de Valorsine 
is a conglomerate, often of considerable thickness, at the base of the 
Carboniferous series in the Western Alps. For its distribution and 
the literature of the subject I may refer to Prof. Favre’s classic 
work— Recherches géologiques de la Savoie, etc. I have examined 
this conglomerate, especially in the neighbourhood of Vernayaz. All 
authors agree that it contains fragments of gneiss and various schists 
with vein quartz. De Saussure, however, states that he did not find 
“any schist (¢.e. slate) simply argillaceous or any limestone.” It 
should, however, be mentioned that he is not speaking quite of the 
same locality as I describe, though he had probably seen it, and 
his remark appears intended to be general. 
The conglomerate, together with a grit and dark slate, which in 
aspect resembles some of the Bala slates of Wales, occurs on the left 
bank of the Rhone, near Vernayaz and the opening of the famous 
Gorge de Trient. This last has been excavated in a hard gneiss, 
and the beautiful Pissevache cascade a little further down the valley 
is precipitated over a similar rock. Between the two, all seemingly 
interstratified, and now in an almost vertical position, come the 
conglomerate, grit, and slate of the Carboniferous series. Of course 
the last is simply caught in a great fold of the earlier rock, after the 
usual Alpine fashion, and there has perhaps also been some further 
disturbance of the nature of faulting. But as no one disputes that 
the gneiss and the conglomerate differ greatly in age, it is needless 
to enter into details on this point. The conglomerate crops out 
along the winding road which leads from the level of the Rhone to 
the elevated bed of the Val de Trient, and can be traced for a very 
considerable distance up the latter valley. 
The conglomerate passes into and is interbanded with grits, and 
these are succeeded by slate, as may be well seen during the above- 
named ascent. The transition from the supposed metamorphic rock 
to the only mechanically altered is so rapid, that our suspicions as to 
the former may well be aroused. The fragments in it are generally 
subangular, of various sizes, commonly up to 2 or 38 inches in 
diameter, but occasionally as much as 5 or 6 inches. The materials 
are chiefly vein-quartz, gneiss, mica-schist, and a purplish argillite. 
The proportions of these rocks vary somewhat, as might be expected. 
The gneiss is a rather fine-grained one, with silvery mica; it belongs 
to the same group as that exposed in the immediate neighbourhood— 
that which in the Alps usually occurs some distance above the coarse 
granitoid gneisses or protogines—the lowest known rocks of the 
district—and the large group of variable schists, part of which is 
the Pietra Verde group of some authors. Silvery mica, however, 
seems more abundant in the fragments than in the rocks which 
occur in situ. The mica-schist is one of the ordinary strongish mica- 
