To the physical geologist the conformation of the Alps, and of mountain-regions generally, constitutes one of the most interesting problems of the present day. To account for this conformation, two hypotheses have been advanced, which may be respectively named the hypothesis of fracture and the hypothesis of erosion. Those who adopt the former maintain that the forces by which the Alps were elevated produced fissures in the earth’s crust, and that the valleys of the Alps are the tracks of these fissures. Those who hold the latter hypothesis maintain that the valleys have been cut out by the action of ice and water, the mountains themselves being the residual forms of this grand sculpture. To the erosive action here indicated must be added that due to the atmosphere (the severance and detachment of rocks by rain and frost), as affecting the forms of the more exposed and elevated peaks.
I had heard it stated that the Via Mala was a striking illustration of the fissure theorythat the profound chasm thus named, and through which the Hinter-Rhein now flows, could be nothing else than a crack in the earth’s crust. To the Via Male, I therefore went in 1864 to instruct myself by actual observation upon the point in question.
The gorge commences about a quarter of an hour above Tusis ; and, on entering it, the first conclusion is that it must be a fissure. This con-elusion in my case was modified as I advanced. Some distance up the gorge I found upon the slopes to my right quantities of rolled stones, evidently rounded by water-action. Still further up, and just before reaching the first bridge which spans the chasm, I found more rolled stones, associated with sand and gravel. Through this mass of detritus, fortunately, a vertical cutting had been made, which exhibited a section showing perfect stratification. There was no agency in the place to roll these stones, and to deposit these alternating layers of sand and pebbles, but the river which now rushes some hundreds of feet below them. At one period of the Via Mala’s history the river must have run at this high level. Other evidences of water-action soon revealed themselves. From the parapet of the first bridge I could see the solid rock 200 feet above the bed of the river scooped and eroded.
It is stated in the guide-books that the river, which usually runs along the bottom of the gorge, has been known almost to fill it during violent thunder-storms ; and it may be urged that the marks of erosion which the sides of the chasm exhibit are due to those occasional floods. In reply to this, it may be stated that even the existence of such floods is not well authenticated, and that if the supposition were true, it would be an additional argument in favour of the cutting power of the river. For if floods operating at rare intervals could thus erode the rock, the same agency, acting without ceasing upon the river’s bed, must certainly be competent to excavate it.
I proceeded upwards, and from a point near another bridge (which of them I did not note) had a fine view of a portion of the gorge. The river here runs at the bottom of a cleft of profound depth, but so narrow that it might be leaped across. That this cleft must be a crack is the impression first produced ; but a brief inspection suffices to prove that it has been cut by the river. From top to bottom we have the unmistakable marks of erosion. This cleft was best seen by looking down-wards from a point near the bridge ; but looking upwards from the bridge itself, the evidence of aqueous erosion was equally convincing.
The character of the erosion depends upon the rock as well as upon the river. The action of water upon some rocks is almost purely mechanical ; they are simply ground away or detached in sensible masses. In other cases the action is chemical as well as mechanical. Water, in passing over limestone, charges itself with carbonate of lime without damage to its transparency ; the rock is dissolved in the water; and the gorges cut by water in such rocks often resemble those cut in the ice of glaciers by glacier streams. To the solubility of limestone is probably to be ascribed the fantastic forms which peaks of this rock usually assume, and also the grottos and caverns which interpenetrate limestone formations. A rock capable of being thus dissolved will expose a smooth surface after the water has quitted it ; and in the case of the Via Mala it is the polish of the surfaces, and also the curved hollows scooped in the sides of the gorge, which assure us that the chasm has been the work of the river.
About four miles from Tusis, and not far from the little village of Zillis, the Via Mala opens into a plain bounded by high- terraces, evidently cut by water. It occurred to me the moment I saw it that the plain had been the bed of an ancient lake ; and a farmer, who was my temporary companion, immediately informed me that such was the tradition of the neighbourhood. This man conversed with intelligence, and as I drew. his attention to the rolled stones, which rest not only above the river, but above the road, and inferred that the river must have been there to have rolled those stones, he saw the force of the evidence perfectly. In fact, in former times, and subsequent to the retreat of the great glaciers, a rocky barrier crossed the valley at this place, damming the river which came from the glaciers higher up. A lake was thus formed which poured its waters over the barrier. Two actions were here at work, both tending to obliterate the lakethe raising of its bed by the deposition of detritus, and the cutting of its dam by the river. In process of time the cut deepened into the Via Mala ; the lake was drained, and the river now flows in a definite channel through the plain which its waters- once totally covered.
From Tusis I crossed to Tiefenkasten by the Schien Pass, and thence over the Julier Pass to Pontresina. There are three or four ancient lake-beds between Tiefenkasten and the summit of the Julier. They are all of the same typea more or less broad and level valley-bottom, with a barrier in front through which the river has cut a passage, the drainage of the lake being the consequence. These lakes are sometimes dammed by barriers of rock, sometimes by the moraines of ancient glaciers.
An example of this latter kind occurs in the Rosegg valley, about twenty minutes below the end of the Rosegg glacier, and about an hour from Pontresina. The valley here is crossed by a pine-covered moraine of the noblest dimensions : in the neighbourhood of London it might be called a mountain. That it is a moraine, the inspection of it from a point on the Surlei slopes above it will convince any person possessing an educated eye. Where, moreover, the interior of the mound is exposed, it exhibits morainematter–detritus pulverised by the ice, with boulders entangled in it. It stretched quite across the valley, and at one time dammed the river up. But now the barrier is cut through, the stream having about one-fourth of the moraine to its right, and the remaining three-fourths to its left. Other moraines of a more resisting character hold their ground as barriers to the present day. In the Val di Campo, for example, about three-quarters of an hour from Pisciadello, there is a moraine composed of large boulders, which interrupt the course of a river and compel the water to fall over them in cascades. They have in great part resisted its action since the retreat of the ancient glacier which formed the moraine. Behind the moraine is a lake-bed, now converted into a meadow, which is quite level, and rests on a deep layer of mould.
At Pontresina a very fine and instructive gorge is to be seen. The river from the Morteratsch glacier rushes through a deep and narrow chasm which is spanned at one place by a stone bridge. The rock is not of a character to preserve smooth polishing ; but the larger features of water-action are perfectly evident from top to bottom. Those features are in part visible from the bridge, but still better from a point a little distance from the bridge in the direction of the upper village of Pontresina. The hollowing out of the rock by the eddies of the water is here quite manifest. A few minutes’ walk up-wards brings us to the end of the gorge ; and behind it we have the usual indications of an ancient lake, and terraces of distinct water origin.
From this position the genesis of the gorge is clearly revealed. After the retreat of the ancient glacier, a transverse ridge of comparatively resisting material crossed the valley at this place. Over the lowest part of this ridge the river flowed, rushing steeply down to join at the bottom of the slope the stream which issued from the Rosegg glacier. On this incline the water became a powerful eroding agent, and finally cut its channel to its present depth.
Geological writers of reputation assume at this place the existence of a fissure, the ‘ washing out’ of which resulted in the formation of the gorge. Now no examination of the bed of the river ever proved the existence of this fissure ; and it is certain that water can cut a channel through unfissured rock that cases of deep cutting can be pointed out where the clean bed of the stream is exposed, the rock which forms the floor of the river not exhibiting a trace of fissure. An example of this kind occurs near the Bernina Gasthaus, about two hours from Pontresina. A little way below the junction of the two streams from the Bernina Pass and the Heuthal the river flows through a channel cut by itself, and 20 or 30 feet in depth. At some places the river-bed is covered with rolled stones ; at other places it is bare, but shows no trace of fissure. The abstract power of water (if I may use the term) to cut through rock is demonstrated by such instances. But if water be competent to form a gorge without the aid of a fissure, why assume the existence of such in cases like that at Pontresina ? It seems far more philosophical to accept the simple and impressive history written on the walls of those gorges by the agent which produced them.
Numerous cases might be pointed out, varying in magnitude, but all identical in kind, of barriers which crossed valleys and formed lakes having been cut through by rivers, narrow gorges being the con-sequence. One of the most famous examples of this kind is the Finsteraarschlucht in the valley of Hasli. Here the ridge called the Kirchet seems split across, and the river Aar rushes through the fissure. Behind the barrier we have the meadows and pastures of Imhof resting on the sediment of an ancient lake. Were this an isolated case, one might reasonably conclude that the Finisteraarschlucht was produced by an earthquake, as some suppose it to have been ; but when we find it to be a single sample of actions which are frequent in the Alpswhen probably a hundred cases of the same kind, though different in magnitude, can be pointed outit seems quite unphilosophical to assume that in each particular case an earthquake was at hand to form a channel for the river. As in the case of the barrier at Pontresina, the Kirchet, after the retreat of the Aar glacier, dammed the waters flowing from it, thus forming a lake, on the bed of which now stands the village of Imhof. Over this barrier the Aar tumbled towards Meyringen, cutting, as the centuries passed, its bed ever deeper, until finally it became deep enough to drain the lake, leaving in its place the alluvial plain, through which the river now flows in a definite channel.’
But the broad view taken by the advocates of the fracture theory is, that the valleys are the tracks of primeval fissures produced by the upheaval of the land, and the cracks across the barriers to which I have referred are in reality portions of the great cracks which formed the valleys. Such an argument, however, would virtually concede the theory of erosion as applied to the valleys of the Alps. The narrow gorges, often not more than twenty or thirty feet across, sometimes even narrower, frequently occur at the bottom of broad valleys. Such fissures might enter into the list of accidents which gave direction to the real erosive agents which scooped the valley out ; but the formation of the valley, as it now exists, could no more be ascribed to it than the motion of a railway train could be ascribed to the finger of the engineer which turns on the steam.
These deep gorges occur, I believe, for the most part in limestone strata ; and the effects which the merest driblet of water can produce on such rocks are quite astonishing. It is not uncommon to meet chasms of considerable depth produced by small streams the beds of which are dry for a large portion of the year. Right and left of the larger gorges such secondary chasms are usually to be found. The idea of time must, I think, be more and more included in our reasonings – on these phenomena. Happily, the marks which the rivers have, in most cases, left behind them, and which refer, geologically considered, to actions of yesterday, give us ground and courage to conceive what may be effected in geologic periods. Thus the modern portion of the Via Mala throws light upon the whole. Near Bergün, in the valley of the Albula, there is also a little Via Mala, which is not less significant than the great one. The river flows here through a profound limestone gorge ; but to the very edges of the gorge we have the evidences of erosion. The most striking illustration of water-action upon limestone rock which I have ever witnessed is, I think, furnished by the gorge at Pfaffers. Here the traveller passes along the side of the chasm midway between top and bottom. Whichever way he looks, backwards or forwards, upwards or downwards, to-wards the sky or towards the river, he meets everywhere the irresistible and impressive evidence that this wonderful fissure has been sawn through the mountain by the waters of the Tamina.
I have thus far confined myself to the consideration of the gorges formed by the cutting through of the rock-barriers which frequently cross the valleys of the Alps ; as far as I have examined them they are the work of erosion. But the large’ question still remains, To what action are we to ascribe the formation of the valleys themselves ? This question includes that of the formation of the mountain-ridges, for were the valleys wholly filled, the ridges would disappear. Possibly no answer can be given to this question which is not beset with more or less of difficulty. Special localities might be found which would seem to contradict every solution which refers the conformation of the Alps to the operation of a single cause.
Still the Alps present features of a character sufficiently definite to bring the question of their origin within the sphere of close reasoning. That they were in whole or in part once beneath the sea will not be disputed; for they are in great part composed of sedimentary rocks which required a sea to form them. Their present elevation above the sea is due to one of those local changes in the shape of the earth which have been of frequent occurrence throughout geologic time, and which in some cases have depressed the land, and in others caused the sea-bottom to protrude beyond its surface. Considering the inelastic character of its materials, the protuberance of the Alps could hardly have been pushed out without dislocation and fracture ; and this conclusion gains in probability when we consider the foldings, contortions, and even reversals in position of the strata in many parts of the Alps Such changes in the position of beds which were once horizontal could not have been effected without dislocation. Fissures would be produced by these changes; and such fissures, the advocates of the fracture theory contend, mark the positions of the valleys of the Alps.
Imagination is necessary to the man of science, and we could not reason on our present subject without the power of presenting mentally a picture of the earth’s crust cracked and fissured by the forces which produced its upheaval. Imagination, however, must be strictly checked by reason and by observation. That fractures occurred cannot, I think, be doubted, but that the valleys of the Alps are thus formed is a conclusion not at all involved in the admission of dislocations. I never met with a precise statement of the manner in which the advocates of the fissure theory suppose the forces to have actedwhether they assume a general elevation of the region, or a. local elevation of distinct ridges ; or whether they assume local subsidences after a general elevation, or whether they would superpose upon the general upheaval minor and local upheavals.
In the absence of any distinct statement, I will assume the elevation to be generalthat a swelling out of the earth’s crust occurred here, sufficient to place the most prominent portions of the protuberance three miles above the sea-level. To fix the ideas, let us consider a circular portion of the crust, say one hundred miles in diameter, and let us suppose, in the first instance, the circumference of this circle to remain fixed, and that the elevation was confined to the space within it. The upheaval would throw the crust into a state of strain ; and, if it were inflexible, the strain must be relieved by fracture. Crevasses would thus intersect. the crust. Let us now enquire what proportion the area of these open fissures is likely to bear to the area of the unfissured crust. An approximate answer is all that is here required ; for the problem is of such a character as to render minute precision unnecessary.
No one, I think, would affirm that the area of the fissures would be one-hundredth the area of the land. For let us consider the strain upon a single line drawn over the summit of the protuberance from a point on its rim to a point opposite. Regarding the protuberance as a spherical swelling, the length of the arc corresponding to a chord of 100 miles and a versed sine of 3 miles is 100.24 miles ; consequently the surface to reach its new position must stretch 0.24 of a mile, or be broken. A fissure or a number of cracks with this total width would relieve the strain ; that is to say, the sum of the widths of all the cracks over the length of 100 miles would be 420 yards. If, instead of comparing the width of the fissures with the length of the lines of tension, we compared their areas with the area of the unfissured land, we should of course find the proportion much less. These considerations will help the imagination to realise what a small ratio the area of the open fissures must bear to the unfissured crust. They enable us to say, for example, that to assume the area of the fissures to be one-tenth of the area of the land would be quite absurd, while that the area of the fissures could be one-half or more than one-half that of the land would be in a proportionate degree unthinkable. If we suppose the elevation to be due to the shrinking or subsidence of the land all round our assumed circle, we arrive equally at the conclusion that the area of the open fissures would be altogether insignificant as compared with that of the unfissured crust.
To those who have seen them from a commanding elevation, it is needless to say that the Alps themselves bear no sort of resemblance to the picture which this theory presents to us. Instead of deep cracks with approximately vertical walls, we have ridges before us running into peaks, and gradually sloping to form valleys. Instead of a fissured crust, we have a state of things closely resembling the surface of the ocean when agitated by a storm. The valleys, instead of being much narrower than the ridges, occupy the greater space. A plaster cast of the Alps turned upside down, so as to invert the elevations and depressions, would exhibit blunter and broader mountains, with narrower valleys between them, than the present ones. The valleys that exist cannot, I think, with any correctness of language be called fissures. It may be urged that they originated in fissures : but even this is unproved, and, were it proved, would still make the fissures play the subordinate part of giving direction to the agents which are to be regarded as the real sculptors of the Alps.
The fracture theory, then, if it regards the elevation of the Alps as due to the operation of a force acting throughout the entire region, is, in my opinion, utterly incompetent to account for the conformation of the country. If, on the other hand, we are compelled to resort to local disturbances, the manipulation of the earth’s crust necessary to obtain the valleys and the mountains will, I imagine, bring the difficulties of the theory into very strong relief. Indeed an examination of the region from many of the more accessible eminences from the Galenstock, the Grauhaupt, the Pitz Languard, the Monte Confinaleor, better still, from Mont Blanc, Monte Rosa, the Jungfrau, the Finsteraarhorn, the Weisshorn, or the Matterhorn, where local peculiarities are toned down, and the operations of the powers which really made this region what it is are alone brought into prominence must, I imagine, convince every physically-minded man of the inability of any fracture theory to account for the present conformation of the Alps.
A correct model of the mountains, with an unexaggerated vertical scale, produces the same effect upon the mind as the prospect from one of the highest peaks. We are apt to be influenced by local phenomena which, though insignificant in view of the general question of Alpine conformation, are, with reference to our customary standards, vast and impressive. In a true model those local peculiarities disappear ; for on the scale of a model they are too small to be visible ; while the essential facts and forms are presented to the undistracted attention.
A minute analysis of the phenomena strengthens the conviction which the general aspect of the Alps fixes in the mind. We find, for example, numerous valleys which the most ardent plutonist would not think of ascribing to any other agency than erosion. That such is their genesis and history is as certain as that erosion produced the Chines in the Isle of Wight. From these indubitable cases of erosioncommencing, if necessary, with the small ravines which run down the flanks of the ridges, with their little working navigators at their bottomswe can proceed, by almost insensible gradations, to the largest valleys of the Alps ; and it would perplex the plutonist to fix upon the point at which fracture begins to play a material part.
In ascending one of the larger valleys, we enter it where it is wide and where the eminences are gentle on either side. The flanking mountains become higher and more abrupt as we ascend, and at length we reach a place where the depth of the valley is a maximum. Continuing our walk upwards, we find ourselves flanked by gentler slopes, and finally emerge from the valley and reach the summit of an open col, or depression in the chain of mountains. This is the common character of the large valleys. Crossing the col, we descend along the opposite slope of the chain, and through the same series of appearances in the reverse order. If the valleys on both sides of the col were produced by fissures, what prevents the fissure from prolonging itself across the col ? The case here cited is representative ; and I am not acquainted with a single instance in the Alps where the chain has been cracked in the manner indicated. The cols are simply depressions , and in the case of many of them the unfissured rock can be traced from side to side.
The typical instance just sketched follows as a natural consequence from the theory of erosion. Before either ice or water can exert great power as an erosive agent, it must collect in sufficient mass. On the higher slopes and plateausin the region of colsthe power is not fully developed ; but lower down tributaries unite, erosion is carried on with increased vigour, and the excavation gradually reaches a maximum. Lower still the elevations diminish and the slopes become more gentle ; the cutting power gradually relaxes, until finally the eroding agent quits the mountains altogether, and the grand effects which it produced in the earlier portions of its course entirely disappear.
I have hitherto confined myself to the consideration of the broad question of the erosion theory as compared with the fracture theory ; and all that I have been able to observe and think with reference to the subject leads me to adopt the former. Under the term erosion I include the action of water, of ice, and of the atmosphere, including frost and rain. Water and ice, however, are the principal agents, and which of these two has produced the greatest effect it is perhaps impossible to say. Two years ago I wrote a brief note ‘ On the Conformation of the Alps,” in which I ascribed the paramount influence to glaciers. The facts on which that opinion was founded are, I think, unassailable ; but whether the conclusion then announced fairly follows from the facts is, I confess, an open question.
The arguments which have been thus far urged against the conclusion are not convincing. Indeed, the idea of glacier erosion appears so daring to some minds that its boldness alone is deemed its sufficient refutation. It is, however, to be remembered that a precisely similar position was taken up by many respectable people when the question of ancient glacier extension was first mooted. The idea was considered too hardy to be entertained; and the evidences of glacial action were sought to be explained by reference to almost any process rather than the true one. Let those who so wisely took the side of boldness’ in that discussion beware lest they place themselves, with reference to the question of glacier erosion, in the position formerly occupied by their opponents.
Looking at the little glaciers of the present daymere pigmies as compared to the giants of the glacial epochwe find that from every one of them issues a river more or less voluminous, charged with the matter which the ice has rubbed from the rocks. Where the rocks are of a soft character, the amount of this finely pulverised matter suspended in the water is very great. The water, for example, of the river which flows from Santa Catarina to Bormio is thick with it. The Rhine is charged with this matter, and by it has so silted up the Lake of Constance as to abolish it for a large fraction of its length. The Rhone is charged with it, and tens of thousands of acres of cultivable land are formed by it above the Lake of Geneva.
In the case of every glacier we have two agents at workthe ice exerting a crushing force on every point of its bed which bears its weight, and either rasping this point into powder or tearing it bodily from the rock to which it belongs ; while the water which everywhere circulates upon the bed of the glacier continually washes the detritus away and leaves the rock clean for further abrasion. Confining the action of glaciers to the simple rubbing away of the rocks, and allowing them sufficient time to act, it is not a matter of opinion, but a physical certainty, that they will scoop out valleys. But the glacier does more than abrade. Rocks are not homogeneous ; they are intersected by joints and places of weakness, which divide them into virtually detached masses. A glacier is undoubtedly competent to root such masses bodily away. Indeed the mere à priori consideration of the subject proves the competence of a glacier to deepen its bed. Taking the case of a glacier 1,000 feet deep (and some of the older ones were probably three times this depth), and allowing 40 feet of ice to an atmosphere, we find that on every square inch of its bed such a glacier presses with a weight of 375 lbs., and on every square yard of its bed with a weight of 486,000 lbs. With a vertical pressure of this amount the glacier is urged down its valley by the pressure from behind. We can hardly, I think, deny to such a tool a power of excavation.
Before concluding these remarks, I refreshed my memory by a second reading of the paper of Mr. John Ball, published in the ‘ Philosophical Magazine’ for February 1863. Mr. Ball’s great experience of the Alps naturally renders everything he writes regarding them interesting. But though I have attended to the suggestions contained in his paper, I am unable to see the cogency of his arguments.
An inspection of the map of Switzerland, with reference to the direction of its valleys, suggests to my mind no objection whatever to the theory of erosion.
The reperusal of his paper assured me that Mr. Ball had paid attention to the formation of ancient lakes. He deems their beds a prominent feature of Alpine valleys ; and he considers the barriers which dammed them up, and which were not removed by the ancient glaciers, as ‘ a formidable difficulty in the way of Prof. Tyndall’s bold hypothesis.’ ‘ Looking at the operation as a whole,’ writes Mr. Ball, ‘ it is to me quite inconceivable that a glacier should be competent to scoop out valleys a mile or more in depth, and yet be unable to remove the main inequalities from its own channel.’
To this I reply that a glacier is competent to remove such barriers, and they probably have been ground down in some cases thousands of feet. But being of more resisting material than the adjacent rock, they are not ground down to the level of that rock. Were its bed uniform in the first instance, the glacier would, in my opinion, produce the inequalities which Mr. Ball thinks it ought to remove. I have recently had the pleasure of examining some of these barriers in the company of Mr. Ball ; and to me they represented nothing more than the natural accidents of the locality. It would, I think, be far more wonderful to find the rocks of the Alps perfectly homogeneous, than to find them exhibiting such variations of resistance to grinding down as are actually observed.
The question of lake-basins is now in competent hands, and on its merits I will offer no opinion. But I cannot help remarking that the dams referred to by Mr. Ball furnish a conclusive reply to some of the arguments which have been urged against Prof. Ramsay’s theory. These barriers have been crossed by the ice, and many of them present steeper gradients than Prof. Ramsay has to cope with in order to get his ice out of his lake basins. An inspection of the barriers shows that they were incompetent to embay the ice; they are scarred and fluted from bottom to top. When it is urged against Prof. Ramsay that a glacier cannot drop into a hole 2,000 feet deep and get out again, the distance ought to be stated over which these 2,000 feet have to be distributed. A depression 2,000 feet deep, if only of sufficient length, would constitute no material obstacle to the motion of a great glacier.
The retardation of a glacier by its bed has also been referred to as proving its impotence as an erosive agent ; but this very retardation is in some measure an expression of the magnitude of the erosive energy. Either the bed must give way, or the ice must slide over itself ; and to make ice slide over itself requires great power. We get some idea of the crushing pressure which the moving glacier exercises against its bed from the fact that the resistance, and the effort to overcome it, are such as to make the upper layers of a glacier move bodily over the lower onesa portion only of the total motion being due to the progress of the entire mass of the glacier down its valley.
The sudden bend in the valley of the Rhone at Martigny has also been regarded as conclusive evidence against the theory of erosion. ‘ Why,’ it has been asked, ‘ did not the glacier of the Rhone go straight forward instead of making this awkward bend ?’ But if the valley be a crack, why did the crack make this bend ? The crack, I submit, had at least as much reason to prolong itself in a straight line as the glacier had. A statement of Sir John Herschel with reference to another matter is perfectly applicable here : ‘ A crack once produced has a tendency to runfor this plain reason, that at its momentary limit, at the point at which it has just arrived, the divellent force on the molecules there situated is counteracted only by half of the cohesive force which acted when there was no crack, viz. the cohesion of the uncracked portion alone. To account then for the bend, the adherent of the fracture theory must assume the existence of some accident which turned the crack at right angles to itself; and he surely will permit the adherent of the erosion theory to make a similar assumption.
The influence of small accidents on the direction of rivers is beautifully illustrated in glacier streams, which are made to cut either straight or sinuous channels by causes apparently of the most trivial character. In his interesting paper ‘ On the Lakes of Switzerland,’ M. Studer also refers to the bend of the Rhine at Sargans in proof that the river must there follow a pre-existing fissure. I made a special expedition to the place in 1864 ; and though I felt that M. Studer had good grounds for the selection of this spot, I was unable to arrive at his conclusion as to the necessity of a fissure.
Again, in the interesting volume recently published by the Swiss Alpine Club, M. Desor informs us that the Swiss naturalists who met last year at Samaden visited the end of the Morteratsch glacier, and there convinced themselves that a glacier had no tendency whatever to imbed itself in the soil. I scarcely think that the question of glacier erosion, as applied either to lakes or valleys, is to be disposed of so easily. Let me record here my experience of the Morteratsch glacier. I took with me in 1864 a theodolite to Pontresina, and while there had to congratulate myself on the invaluable aid of my friend Mr. Hirst, who in 1857 did such good service upon the Mer de Glace and its tributaries. We set out three lines across the Morteratsch glacier, one of which crossed the ice-stream near the well-known hut of the painter Georgei, while the two others were staked out, the one above the hut and the other below it. Calling the highest line A, the line which crossed the glacier at the hut B, and the lowest line C, the following are the mean hourly motions of the three lines, deduced from observations which extended over several days. On each line eleven stakes were fixed, which are designated by the figures 1, 2, 3, &c. in the Tables.
Morteratsch Glacier, Line A.
No. of Stake. Hourly Motion.
1 0.35 inch. 2 0.49 3 0.53 4 0.54 5 0.56 6 0.54 7 0.52 8 0.49 9 0.40 10 0.29 11 0.20
As in all other measurements of this kind, the retarding influence of the sides of the glacier is manifest: the centre moves with the greatest velocity.
Morteratsch Glacier, Line B.
No. of Stake. Hourly Motion.
1 0.05 inch. 2 0.14 3 0.24 4 0.32 5 0.41 6 0.44 7 0.44 8 0.45 9 0.43 10 0.44 11 0.44
The first stake of this line was quite close to the edge of the glacier, and the ice was thin at the place, hence its slow motion. Crevasses prevented us from carrying the line sufficiently far across to render the retardation of the further side of the glacier fully evident.
Morteratsch Glacier, Line C.
Nn of Stake. Hourly Motion.
1 0.05 inch. 2 0.09 3 0.18 4 0.20 5 0.25 6 0.27 7 0.27 8 0.30 9 0.21 10 0 20 11 0.16
Comparing the three lines together, it will be observed that the velocity diminishes as we descend the glacier. In 100 hours the maximum motion of the three lines respectively is as follows :
Maximum Motion in 100 hours.
Line A . 56 inches B . 45 C . 30
This deportment explains an appearance which must strike every observer who looks upon the Morteratsch from the Piz Languard, or from the new Bernina Road. A medial moraine runs along the glacier, commencing as a narrow streak, but to-wards the end the moraine extending in width, until finally it quite covers the terminal portion of the glacier. The cause of this is revealed by the fore-going measurements, which prove that a stone on the moraine where it is crossed by the line A approaches a second stone on the moraine where it is crossed by the line C with a velocity of twenty-six inches per one hundred hours. The moraine is in a state of longitudinal compression. Its materials are more and more squeezed together, and they must consequently move laterally and render the moraine at the terminal portion of the glacier wider than above.
The motion of the Morteratsch glacier, then, diminishes as we descend. The maximum motion of the third line is thirty inches in one hundred hours, or seven inches a daya very slow motion ; and had we run a line nearer to the end of the glacier, the motion would have been slower still. At the end itself it is nearly insensible. Now I submit that this is not the place to seek for the scooping power of a glacier. The opinion appears to be prevalent that it is the snout of a glacier that must act the part of ploughshare ; and it is certainly an erroneous opinion. The scooping power will exert itself most where the weight, and consequently (other things being equal) the motion, is greatest. A glacier’s snout often rests upon matter which has been scooped from the glacier’s bed higher up. I therefore do not think that the inspection of what the end of a glacier does or does not accomplish can decide this question.
The snout of a glacier is potent to remove any-thing against which it can fairly abut ; and this power, notwithstanding the slowness of the motion, manifests itself at the end of the Morteratsch glacier. A hillock, bearing pine-trees, was in front of the glacier when Mr. Hirst and myself inspected its end ; and this hillock is being bodily removed by the thrust of the ice. Several of the trees are over-turned ; and in a few years, if the glacier continues its reputed advance, the mound will certainly be ploughed away.
I will here record a few other measurements executed on the Rosegg glacier: the line was staked out across the trunk formed by the junction of the Rosegg proper with the Tschierva glacier, a short distance below the rocky promontory called Agaliogs.
No. of Stake. Hourly Motion.
1 0.01 inch. 2 0.05 3 t.07 4 0.10 5 0.11 6 0.13 7 0.14 8 0.18 9 0.24 10 0.23 11 0.24
This is an extremely slowly moving glacier ; the maximum hardly amounts to seven inches a day. Crevasses prevented us from continuing the line quite across the glacier.
To return to the question of Alpine conformation : it stands, I think, thus : We have, in the first place, great valleys, such as those of the Rhine and the Rhone, which we might conveniently call valleys of the first order. The mountains which flank these main valleys are also cut by lateral valleys running into the main one, and which may be called valleys of the second order. When these latter are examined, smaller valleys are found running into them, which may be called valleys of the third order. Smaller ravines and depressions, again, join the latter, which may be called valleys of the fourth order, and so on until we reach streaks and cuttings so minute as not to merit the name of valleys at all. At the bottom of every valley we have a stream, diminishing in magnitude as the order of the valley ascends, carving the earth and carrying its materials to lower levels. We find that the larger valleys have been filled for untold ages by glaciers of enormous dimensions, always moving, grinding down and tearing away the rocks over which they passed. We have, moreover, on the plains at the feet of the mountains, and in enormous quantities, the very matter derived from the sculpture of the mountains themselves.
The plains of Italy and Switzerland are cumbered by the débris of the Alps. The lower, wider, and more level valleys are also filled to unknown depths with the materials derived from the higher ones. In the vast quantities of moraine-matter which cumber many even of the higher valleys we have also suggestions as to the magnitude of the erosion which has taken place. This moraine-matter, more-over, can only in small part have been derived from the falling of rocks upon the ancient glacier it is in great part derived from the grinding and the ploughing-out of the glacier itself. This accounts for the magnitude of many of the ancient moraines, which date from a period when almost all the mountains were covered with ice and snow, and when, consequently, the quantity of moraine-matter derived from the naked crests cannot have been considerable.
The erosion theory ascribes the formation of Alpine valleys to the agencies here briefly referred to. It invokes nothing but true causes. Its artificers are still there, though, it may be, in diminished strength ; and if they are granted sufficient time, it is demonstrable that they are competent to produce the effects ascribed to them. And what does the fracture theory offer in comparison? From no possible application of this theory, pure and simple, can we obtain the slopes and forms of the mountains. Erosion must in the long run be invoked, and its power therefore con-ceded. The fracture theory infers from the disturbances of the Alps the existence of fissures ; and this is a probable inference. But that they were of a magnitude sufficient to determine the conformation of the Alps, and that they followed, as the Alpine valleys do, the lines of natural drainage of the country, are assumptions which do not appear to me to be justified either by reason or by observation.
There is a grandeur in the secular integration of small effects implied by the theory of erosion almost superior to that involved in the idea of a cataclysm. Think of the ages which must have been consumed in the execution of this colossal sculpture. The question may, of course, be pushed to further limits. Think of the ages which the molten earth required for its consolidation. But these vaster epochs lack sublimity through our inability to grasp them. They bewilder us, but they fail to make a solemn impression. The genesis of the mountains comes more within the scope of the intellect, and the majesty of the operation is enhanced by our partial ability to conceive it. In the falling of a rock from a mountain-head, in the shoot of an avalanche, in the plunge of a cataract, we often see more impressive illustrations of the power of gravity than in the motions of the stars. When the intellect has to intervene, and calculation is necessary to the building up of the conception, the expansion of the feelings ceases to be proportional to the magnitude of the phenomena.