May 8, 1884] 



NA TURE 



45 



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 

 schisl is only the consolidated debris of micaceous rocks. Its 

 composition, and that of the conglomerate, justifies us in assert- 

 ing that when the Carboniferous rocks of the Valorsine were 

 ited there were land surfaces of gneiss and schist in the 

 western region of the Alps, and that these rocks were sub- 

 stantially 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 for 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 per- 

 sonal 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: — (i) That there has been one epoch, at least, of 

 mountain-making posterior to the deposition of the Miocene 

 nagelflue, 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 we 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 Schei- 

 • leck, over the beds of the nagelflue ; (3) that there was a pre- 

 Triassic land surface of great extent, largely composed of crys- 

 talline rocks, and that with this geological age commenced a 

 long continuous period of depression, lasting into Tertiary times ; 

 (4) that a land surface of considerable extent existed at a yet 

 earlier period, and that this in the Carboniferous age was watered 

 by streams and clothed with vegetation — whether there were 

 mountains then it is impossible to say, but the evidence certainly 

 points to the conclusion that the ground was hilly ; (5) that 

 interior to the last-named period there is a great gap in our 

 records ; the older rocks, whose stratigraphical position can be 

 ascertained, being much metamorphosed, so that we appear 

 justified in concluding that all the more important mineral 

 changes which they had undergone occurred in pre-Carboniferous 

 times — that is, that the later Palaeozoic land surfaces consisted of 

 gneiss and schists in all important respects identical with those 

 which now exist. 



I have thus led you step by step — by processes, I trust, of 

 cautious induction — to the result that the Alps, as an irregular 

 land surface, are a very ancient feature in the contour of the 

 earth, and that the gneisses and crystalline schists, whereof they 

 so largely consist, are rocks of very great antiquity. Let us now 

 attempt to advance a step further by attacking the problem from 

 another side. Hitherto we have been working downwards from 

 the newer to the older, from the rocks of known towards those of 

 unknown date. Beginning now in the unknown, beginning 

 with the most remote that we can find, let us proceed onwards 

 toward the more recent and more recognised. 



This is a task of no slight difficulty. The ordinary rules of 

 stratigraphical inference frequently fail us ; nay, if blindly fol- 

 lowed, would lead us to the most erroneous conclusions. In the 

 apparent succession of strata in a mountain range the last may be 

 first and the first last in the literal sense of the words. Beds 

 may be repeated again and again by great folds, now in the 

 direct, now in the inverse, order of their superposition. They 

 may have been faulted and then folded, or folded and then 

 faulted, and the difficulty is augmented by the vast scale on 

 which these earth movements have taken place, by the frequent 

 impossibility of scaling the crags or pinnacles where critical 

 sections are disclosed, and by the masking of large areas of 

 surface by snow and glacier, or by debris and vegetation. Vet 

 more, the consciousness of these difficulties produces in the 

 mind — I speak for myself — a sort of hesitation and scepticism, 

 which are most unfavourable for inductive reasoning. Knowing 

 not what features are of importance, one is perplexed by the 

 variety of facts that seem to call fir notice ; knowing how easily 



one may be deceived, one hesitates to draw conclusions. I am 

 often painfully conscious of how much I have lost in a previous 

 journey from not having remarked some fact to which a fortunate 

 accident has just compelled my attention. In this part, there- 

 fore, I must be pardoned if I speak with considerable hesitation 

 and do not attempt more than state those inferences which seem 

 to me warranted by facts. 



I shall again ask permission to conduct you to a series of 

 typical sections, which, however, I shall describe with less 

 minuteness. 



Let us place ourselves in imagination on the great ice-field at 

 the upper part of the Gross Aletsch Glacier — the Place de la 

 Concorde of Nature, as it has been happily termed. We are 

 almost hemmed in by some of the loftiest peaks of the Bernese 

 Oberland : the Aletschhorn, the Jungfrau, the Monch, and 

 several others. We find the rocks which rise immediately round 

 the glacier — as, for example, near the well-known Concordia hut 

 — to be coarse gneisses, with difficulty distinguishable from 

 granites. As the eye travels up to any one of the mountain 

 ridges, the rock evidently becomes less massive and more dis- 

 tinctly foliated. We note the same sequence as we retrace our 

 steps towards the Rhone valley — speaking in general terms, the 

 ridges and the flanks of the Eggischhorn consist of more finely 

 granulated gneisses and of strong micaceous schists, which 

 'alternate more frequently one with another. Further to the 

 west, in the region around the Oberaletsch Glacier and on the 

 slopes of the Bell Alp, we find the same succession — coarse 

 granitoid gneisses in the relatively lower part of the heart of the 

 chain, finer grained and more variable gneisses and schists on 

 the upper ridges and the southern flanks. 



Let us change our position to a spot considerably to the east, 

 to the great section of the crystalline series made by the valley 

 of the Reuss below Andermatt. 



From the spot where the rocks close in suddenly upon the 

 torrent near the Devil's Bridge, to a considerable distance below 

 Wasen, extends an almost unbroken mass of coarse granitoid 

 gneiss. This, however, becomes more distinctly bedded and 

 schistose before it entirely disappears beneath the Secondary 

 deposits that border the Bay of Uri. Similarly, if from Wasen, 

 where the gneiss is barely distinguishable from granite, we ascend 

 the wild glen which leads up to the Susten Pass, and descend on 

 the other side by the grand scenery of the Stein Alp to the 

 beautiful Gadmenthal, thus passing obliquely outwards along the 

 apparent strike of the rocks to the point where, as in the neigh- 

 bourhood of the Imhof, they disappear beneath Mesozoic deposits, 

 we again find that we are among rocks which are rather more 

 variable in their mineral character, oscillating between moder- 

 ately coarse gneisses, sometimes porphyritic, and strong mica 

 schists. Near Muhlestalden, in the Gadmenthal, even a bed of 

 white crystalline dolomitic limestone is interstratified with the 

 gneissic rocks. 



Leaving for a brief space the vicinity of the St. Gothard road, 

 and returning to the upper valley of the Rhone, let us place our- 

 selves on such an outlook as we can obtain from Prof. Tyndall's 

 chalet on the Bell Alp, and fix our eyes on the magnificent 

 panorama of the Pennine chain, with whose geology we will 

 suppose ourselves to have become familiar in frequent traverses 

 from the northern to the southern side of the watershed of Central 

 Europe. Facing us, and forming the lower slopes and crags of 

 the great mountain chain «f the Pennines, we see an enormous 

 mass of distinctly bedded rock, of a brownish tint, of which at 

 this distance we should hesitate to say whether we ought to re.' n id 

 it as a member of the metamorphic or of the ordinary sedin c ntary 

 series. In an east-north-east direction we see it gradually ; ising to 

 form the peak of the Ofenhorn and the upper part of the r ountains 

 about the Gries Pass. In the opposite direction it forms he lower 

 slopes of the Simplon Pass and the portals of the valley of the 

 Visp. Hence, could we follow it, the area occupied by this rock 

 broadens out into the spurs which inclose the Einfischthal and the 

 Eringerthal, and crosses the watershed towards the south to the 

 east of the St. Bernard Pass. In more than one locality in the 

 region of the Binnenthal a band, of no great vertical thickness, , f 

 a white crystalline dolomite is conspicuously present. A very 

 similar group of rocks occurs in the Val Piora, in some bands of 

 which black garnets are very abundant. The same mineral also 

 occurs in a similar rock near the summit of the Gries Pass. Anda- 

 lusite or staurolite also occurs occasionally ; the group, in short, 

 is well characterised, and for reference I will call it the Lustn us 

 Schists. 



