66 Professor T. G. Bonney [April 4, 



There remains yet one other section to wliich I wish to direct your 

 attention ; it is near Vernayaz, in the vicinity of the famous gorge of 

 the Trient. Where the Ehone bends, at Martigny, from a south-west 

 to a north-west course, the crystalline massif of the Mont Blanc region 

 of which we have just spoken crosses the river, and is lost to sight 

 as it plunges beneath the mesozoic rocks of the western summits of 

 the Oberland. The gorge of the Trient is cut through hard and 

 moderately coarse gneiss ; the same rock occurs at the Sallenche 

 waterfall. Between the two is a mass of rock of a totally different 

 character — in part a dark slate, like some in Britain of Lower Silurian 

 age ; in part a conglomerate or breccia in a micaceous matrix, proved 

 by its plant remains to be a member of the Carboniferous series. 

 Omitting some minor details, not without interest, it may suffice to 

 say that we have in this place the end of an almost vertical loop, 

 formed by the folding of beds of Carboniferous age between the 

 crystalline rocks, which are the foundation-stones of the district. 

 The conglomerate is at the base of the Carboniferous series, and its 

 matrix so closely resembles a mica schist, that it has been claimed as 

 indicating metamorphism, and as linking together the Carboniferous 

 slates and the crystalline schists. But, in the first place, the fragments 

 in the conglomerate are not only gneisses and schists, but also 

 ordinary slaty rocks, no more altered than those of Llanberis. How, 

 we may well ask, could the latter escape unchanged when all the 

 surrounding matrix was converted into mica schist? Further, 

 when we apply the test of the microscope — that Ithuriel spear by 

 which the deceits of rocks are so often revealed — we find that this 

 seeming mica schist is only the consolidated debris of micaceous 

 rocks. Its composition, and that of the conglomerate, justifies us in 

 asserting that when the Carboniferous rocks of the Valorsine were 

 deposited there were land surfaces of gneiss and schist in the western 

 region of the Alps, and that these rocks were substantially identical 

 with those through which the Trient has sawn its ravine. 



It would be easy to multiply instances similar to one or the other 

 of those quoted above from this or that district of the Alpine region, 

 from the south of Monte Viso to the north of the Adriatic, to speak 

 only of those districts of which I have a personal knowledge ; but I 

 should speedily weary you, and will ask you to regard these as typical 

 cases, single samples of a great collection. They justify, as I think you 

 will agree, the following inferences : (1) That there has been one epoch, 

 at least, of mountain-making posterior to the deposition of the 

 Miocene nagclflue, which has given to many parts of the Alpine chain 

 an uplift sometimes not less than a mile in vertical elevation ; (2) 

 that prior to this there was an earlier epoch of mountain-making, 

 which affected all the rocks of older date, including at any rate a 

 portion of middle Eocene age — for wc find marine strata of this date 

 crowning the summit of the Diablerets, now more than 10,000 feet 

 above the sea, and bent back, as at the Rigi Scheideck, over the beds 

 of the nagelflue ; (3) that there was a pre-Triassic land surface of great 



