CHAPTER II.THE ALPS—MONT BLANC.
The Pennine or Western Alps constitute the loftiest group of mountains in Europe. They consist of a vast chain of isolated peaks, all of which are elevated above the region of perpetual snow. Mont Blanc, Mont Cervin, and Mont Combin attain respectively to the heights of fifteen thousand seven hundred and thirty-two feet, fourteen thousand eight hundred and fifty-five feet, and fourteen thousand one hundred and twenty-five feet, above the level of the sea. This group is succeeded by that of the Bernese Alps, of which the Jungfrau is the most conspicuous, reaching the altitude of thirteen thousand seven hundred and eighteen feet. The Helvetian Alps lie to the east and south of these two ranges, rising in Mont Rosa to the height of fifteen thousand one hundred and fifty feet into the same aerial frozen regions. The rivers Rhine and Rhone spring from the glaciers which occupy the valleys intermediate betwixt the Bernese and Helvetian mountains, while the Po, rising among the Cottian Alps on the south-west, derives its principal tributaries from the same alpine sources with its larger twin-sisters.
Switzerland, thus bounded on the south, is walled in along the entire northern frontier by the range of the Jura mountains, whose loftiest point, the Le Reculet, is five thousand six hundred and twenty-seven feet above the sea level. The mountains of Savoy stretch along the left bank of the Lake of Geneva. Mont Pilatus, the Rigi, and other noted hills of tourists, occupy the eastern central division of the country, among which are situated the largest cluster as well as the most celebrated of the lakes. The great valley of Switzerland, the territory proper of the cantons Vaud, Fribourg, Berne, and Soleure—within which lie all theprincipal towns, those of the old Roman and all of modern times—forms an extended plateau or basin, inclosed by an amphitheater of mountain land, diversified at intervals by low swelling ridges, undulating hills, precipitous ravines, the deep-set channels of turbid streams, and lovely lakes imbosomed in orchards, vineyards, and meadows of the most luxuriant pasturage.
The two great rivers, embracing the entire drainage of the country and of all the lakes, debouch through narrow gorges at opposite sides of the Swiss territory, and pursue, nearly at right angles to each other, their respective courses until they mingle their waters—the one in the Mediterranean, and the other in the Northern Ocean.
The little town of Neufchâtel, so often alluded to, lies on the north bank of the lake of the same name, the Jura mountains gently sloping up behind. In the suburbs, forming one of a row of detached unpretending houses, is situated the neat château of M. Agassiz in the middle of a small garden, which rests against the hills, and is bounded on the south by the waters of the lake. A most fitting habitation for the great ichthyologist, surrounded as it is with the noblest scenery, and replete in every locality with the richest treasures of his favorite study. I visited the place in the autumn of 1846, unfortunately when M. Agassiz had just left for America: in a beautiful evening strolled through the garden and adjoining inclosures, and was pleased to observe numerous traces in the rocks, and in some fossil relics lying about, of his studies and researches.
The geology of the Alps, the last stage in our self-elected course, is of the most complicated character. The researches of Studer, Escher, and Brunner, natives of the country, have served to establish the general superposition and normal arrangement of the various groups of strata, as those of the illustrious De Saussure had long before been directed to determine their mineral distinctions, and chiefly their classification upon mineralogical principles, into separate crystalline masses. The labors again of Brongniart, Deshayes, Agassiz, D’Orbigny, and Brown, have been mainly employed upon their organic remains, with a view to ascertain the geological epochs within which the several suites of rocks have originated. Our own countrymen, Buckland, Lyell,Sedgwick, and Murchison, have attempted to systematize still further the alpine deposits, as well as those of Italy and Germany, by showing their relations to the well-marked divisions of our British systems; and the result is, that over all these widely-extended regions, and amidst all the metamorphism, contortion, dislocation, and upheaval of such lofty ranges, there is a true transition from the Silurian, Devonian, and Carboniferous rocks existing in the eastern Alps into the higher secondary and tertiary strata of the western or Swiss Alps.
It would be impossible within our limits to furnish even a moiety of the details and evidences by which the intricate structure of the Alps has been so successfully unraveled, and the arrangement of nature in the due order of superposition so persistently maintained. We shall simply advert to the equivalents of the English strata which have been satisfactorily ascertained, and shall then consider some of the more interesting phenomena connected with the age, elevation, erratic blocks, and glaciers of this Alpine country.
I.General Structure.The great central axis of the Alpine region, stretching from the Rhone to the Danube, consists mainly of the primary crystalline rocks. The granite is everywhere accompanied by gneiss, mica-schist, chlorite-schist, silicious and serpentine limestones. The upper silurian, devonian, and carboniferous systems are distinctly represented in the eastern Alps; but no traces of the Permian deposits have been detected in them or in any part of southern Europe; while again in following the central parts of the chain from Austria into Switzerland and Savoy, all fossil evidences of the four sedimentary systems disappear. The conclusion arrived at by geologists, therefore, is that for these palæozoic and triassic formations there exist no representatives among any of the vast piles of strata of the western Alps; or, if they ever had a place in this part of the chain, that they have been obliterated by the powerful transmuting action of metamorphism, or plunged to inaccessible depths beneath the upraised edges of the primary series. Coal plants, and anthracite coal itself, have both indeed been found in the valley of the Arve in Savoy, at Tarentaise, Maurienne, and along the base of MontBlanc; but as they occur in connection with belemnites, these beds have been referred by M. E. de Beaumont and others to the Lias formation, which is clearly determined by its numerous animal fossils to exist in this part of the chain. The remarkable picturesque rocks of Varennes, Duron, and the Col de Balme belong to the lias deposit—the grandest specimens, perhaps, of natural architecture anywhere to be seen.
But, making allowance for all the uncertainties of their lithological complement, and quitting all points of a doubtful character, it has been satisfactorily established that the flanks of the Swiss Alps are covered by a series of sedimentary deposits of vast thickness, which form a true transition from the newer secondary into the older tertiary strata. The normal arrangement of rocks within these limits is complete, beginning with the lias and terminating in distinctly recognized beds of the tertiary pleiocene group.
The lias formation is largely developed along the northern, eastern, and south-western side of the chain, forming an immense belt from near the foot of the Jungfrau, in the central district of Switzerland, to Savona in the Gulf of Genoa. The oolitic formation succeeds, on a scale of still greater magnitude, having a continuous stretch from the Mediterranean at Toulon to Vienna, on the Danube; again constituting an enormous deposit along the Jura range of mountains; and then by Ulm, Altmuhl, and Amberg, to Beyruth, with its celebrated bone caves, in the heart of Germany. The Oxfordian group are represented by the “Neocomian” limestones, a series of hard subcrystalline strata, abounding in fossils of the gault and upper green-sand. To these succeed beds of red, gray, and white marly limestones, containingGryphææ,Inocerami, andAnanchytes, and regarded as the equivalents, as they are undoubtedly in the position, of the white chalks of England. A supercretaceous group, consisting of nummulitic and shelly rocks, the “flysch” of the Swiss, constitutes the close of the secondary, and graduates conformably and insensibly upward, by mineral and zoological passages, into the eocene system. The vast beds of strata, which are termed the “molasse” and “nagelflue,” contain in thelowerseries a large proportion of living species of marine shells, while the associated andoverlayingstrata of terrestrial origin are loaded with forms all of which are extinct. In this group there is nevertheless shadowed forth a type of rocks characteristic both of a miocene and pleiocene age; but so anomalous is their arrangement, that the younger are often found to dip under the older rocks out of which they have been formed. And as of these, so generally of the entire Alpine series now referred to, the position of the various groups in particular localities can only be unraveled in their flexures, dislocations, and displacements, by means of the organic remains with which they severally abound.
II. TheSuperficial Accumulationsembrace a wide-spread class of geological phenomena. These have originated in causes some of which are still in active operation, others are dormant, and others again may be considered as belonging to agencies which may be termed extraordinary, or permitted only at intervals to display themselves. The effects of their operations are visible, less or more, in every part of the surface of the globe. They have been termed thePleistocenegroup, and consist of both marine and fresh water materials. To these are referred the bowlder-clay formation, the vast deposits of sand and gravel heaped up in valleys, the erratic blocks spread over hill-tops, and the various kinds of detrital matter which, although often laminated, is loose and unstratified, and clearly distinguishable from the more indurated and subjacent beds composing the earth’s crust. Nor in gathering up the links of this extended field of review, will it be possible to omit all mention of glaciers and their moraines, so intimately connected with Alpine scenery.
The sand, gravel, and drift accumulations of every kind are common to every country where waters flow or valleys exist. They cover the great straths of Scotland, the low steppes of Russia, the lofty gorges of the Himalaya, the desert wastes of Africa, and the elevated plateaux of North and South America. Among the Rocky Mountains they are of the most varied character, and are spread over extensive areas in those sterile regions, high up among the sources of the great American rivers. Wherever a stream falls into another stream, a stream into a lake, a lake into a river, or a river into the sea, bars, gravelly shoals, anddeltas are found to exist, or to be in the act of formation. Accumulations of this class, therefore, are to be regarded as of various periods, as they are evidently the results of causes of continual operation, ordinary as well as extraordinary. Many of such phenomena, however, are as clearly the indication of a state of things which no longer exists. Whether by a subsidence in the sea-bottom, or an elevation of the land, they are now raised far above the influence of the element within which they were collected, and to whose abrading powers they owe their laminated structure. Such, in particular, are those regular-shaped terraces as well as detached hillocks of sand and gravel, several hundred feet in depth, so common in the straths of Scotland and valleys of Switzerland, through which arms of the sea or of great inland lakes once penetrated, and over whose shores and bottoms the debris of the mountains gradually accumulated. “The Sea Margins,” the work of the accomplished Robert Chambers, contains a minute and interesting detail of these facts, gleaned from varied sources of reading and most extensive personal observation, and clearly warranting the inference that the sea at no very remote period covered vast districts of country from which it has now receded.
The Bowlder Clayimmediately underlies the gravelly beds which have been noticed. Betwixt the two classes of drift there is a clear line of demarkation, although both sand and gravel are often in considerable masses included in the plastic mud which chiefly characterizes the bowlder clay. This formation is of great extent, covering the whole of the north of Europe, a large portion of northern Asia, and in America extending from the Arctic Sea to Boston; massed up in every ravine, and ranging from the lowest valleys to two thousand feet on the mountain slopes, where it is often accumulated to a great depth. One striking peculiarity of the bowlder clay is, that huge blocks of stones of all ages are imbedded in the mass in every region and country where it is found: hence the name. The bowlders are not always of local origin; on the contrary, the parent rock is more generally situated at remote distances, even from five to eight hundred miles. Thus the Scottish Grampians furnish the greater proportion of the hugeblocks which are scattered over the lowland and midland counties of Scotland. The Lammermuirs, the Cheviots, the Lake Mountains of Cumberland, have strewed their wreck over the vales of the Tweed and Northumberland, through Yorkshire and the midland plains of England. The chalks of Denmark and Norway are spread out on every shoal and bank in the German Ocean to the British shores; while again, through all Friesland and central Germany, the primary rocks of Scandinavia are as distinctly to be traced. The erratic-block family have in like manner traveled over France, those of Britanny and Normandy penetrating to the basin of the Loire; the Cantal down even to the shores of the Mediterranean. Switzerland, perhaps, contains the most interesting specimens of this universal drift-wreck; as, on the sides of the Jura, at an elevation of four thousand feet, at Monthey, where they give a feature to the landscape, and on the east bank of the lake of Geneva, lies the celebratedPierre de Gouté, which figures in the Huttonian controversy, measuring about ten feet in height by fifteen to twenty in breadth and length. Mont Blanc is conjectured to have been the source of most of thesepierres roulés, which have been transported across the valley of the Rhone, or lifted sheer over the mountains of Savoy, and are now at the distance of sixty and seventy miles, lying in all the passes and ridges of the Jura.
Various explanations have been given of the origin and deposition of the bowlder-clay formation, as well as of the erratic block-drift, for the two can scarcely be separated in the question of cause and effect. The bowlders, for example, are sometimes in the mass of clay itself, sometimes they are lying loose on the surface, in many instances they are spread over areas where no clay exists; but in most cases maintaining their unmistakable character of being water-worn, rounded, and covered with striæ. Both classes of phenomena, therefore, are supposed to be referable to the same period of time, as they probably have originated in the same series of causes. One theory advanced in explanation of both, is the agency of powerful currents that swept over Britain and the adjacent continents, generally in a north and north-westerly direction, bearing along with them soil, gravel, and the larger debris of rocks; and as obstructions occurred, or theviolence of the currents subsided, the heterogenous materials were deposited in the various countries and at the different elevations in which they are found. The direction of the currents, often from different centers, is indicated clearly by the position and lithology of the mountains from which the blocks have been transported, no less than by the fact that the greatest accumulations of drift and bowlders are to be observed at the south-eastern extremities of such gorges and valleys as were open to the diluvial action. But the hypothesis fails in giving a satisfactory account of the transport of the larger blocks, often of sixty to a hundred tons weight, over a course of many hundreds of miles, plunging through hollows, and now stranded on mountain slopes several thousand feet above. The theory of icebergs, as the transporting agency, meets this difficulty; and accordingly, in one form or other, such a cause or agent, of widely-prevailing influence, is almost universally adopted into the creed of geologists. This theory implies, that those portions of Europe now covered with the bowlder-clay formation were submerged after the deposition and consolidation of the tertiary strata—that this submergence was the result of a change in the earth’s axis or some extraordinary alteration in its planetary relations—that a great arctic glacial continent subsided and disappeared beneath the waters—and that vast floating masses of ice, inclosing rock loosened from the sinking land, penetrated southward, grazing and polishing the harder substances that lay in their course, or carrying along with them the more yielding and transportable materials. Admit all or even a limited number of such assumptions, and we know from what is occurring in recent times, that the cause is quite adequate to the production of the effect. Sir James Ross, in his late humane exploratory expedition, encountered in the polar regions icebergs from a hundred to three hundred feet in height, and from a quarter to half a mile in length. Two-thirds of every iceberg float beneath the water. What a carrier power, at once for erosion and transport, in every one of these frozen floating mountains! The Polar ocean still maintains its great southward current to the equatorial seas, modified by the headlands and inequalities of bottom which occur in its progress; and then, as now, the icebergs driven along this highway of waterswould drop, at intervals, portions of their stony load, to take up at other stations whatever was prepared to adhere to them. Hence the difficulty vanishes as to the large detached blocks so often found on the elevated sides of mountains. Hence, too, the explanation of those collected groups which are entirely free from any admixture of clay. And hence, upon the retreat of the waters and the elevation of the land, it is reasonable to infer that many districts would be swept bare again of their mud, while the bowlders would remain, and that in other quarters ridges and the deeper accumulations would be formed. “Both theories,” however, as stated by Mr. Page in his excellent treatise, “Rudiments of Geology,” “are beset with difficulties; and though the latter accounts more satisfactorily for most of the phenomena of the erratic block group, still there are many points respecting the distribution and extent of the deposit to be investigated before either can be finally adopted. All that can be affirmed in the present state of the science is the composition and nature of the clay, gravel, and bowlders—the course of the currents concerned in their deposition—the fact of the land having a configuration of hill and valley, not differing much from what now exists—and the peculiar scantiness, if not total absence, of organic remains.”
Whether this mysterious cataclysm occurred before or within the modern epoch is a question which, as yet, has not by any means been determined. The few organic remains detected in the deposit are of marine origin—one or two species of shells—but all identical with species now existing. The presumption is that the climate which prevailed over these northern regions during the period was extremely low. But how long it lasted, and why there are no types preserved, in all that congeries of materials of theterrestrialfauna and flora of the period, are points both of them of a very perplexing kind. Whether just dawning upon the advent of man, or within the actual era of his history, certain it is that these are the results of a chaotic condition over a large portion of our planet, of which, if we except the deluge, we have no record nor memorials in any of the after changes and modifications of its surface. Shall we add, as indicative of afinal causeappearing in and overruling the tumultuous agitation, that to thissource is to be traced great part of the soil which covers the valleys and mountain sides of all the submerged districts? that hereby extensive lakes were silted up, the flinty rock concealed by fertile earth, and the steep acclivity made accessible to the husbandman? One thing is clear, that all the latest tertiary strata in this alpine region have, after their consolidation, been disturbed and broken up: it is upon their inverted edges that the superficial accumulations have been deposited and now rest: and whether the submergence of Europe, and other parts of the globe, was simultaneous or not with the cause of their movement and overthrow, a superintending wisdom and purpose are unquestionably discernible in those accessions of soil and other economic arrangements that resulted from the change.
There is another theory, however, which has been applied to the explanation of these phenomena—namely, thetheory of glaciers, as illustrated in the works of Venetz, Charpentier, Agassiz, and Forbes.
A glacier is a moving stream of ice formed in the transverse valleys and furrowed gorges of alpine chains. They are of great depth and indefinite length; and as they proceed slowly but progressively in their courses they carry along with them all the loose and prehensible mountain debris with which they come in contact. On their surface they bear every falling splinter, small and great, from the overhanging rocks. The sides and bottom of the ravines through which they pass are stripped, polished, and striated. The avalanche breaks upon them with its accumulated load; and every mountain rill, upon the melting of the snows in summer, deposits over their flanks the materials with which they are charged. Immense masses of matter are, in these various ways, collected and transported from the higher into the lower valleys: these at the outgoing of the glacier generally assume a ridge shaped form, and are termedmoraines. The underlying blocks are all rounded and grooved: those borne on the surface are sharp and angular, until they are swept away by the torrents into the rivers, where they are in turn subjected to their smoothing operations. There can be no doubt, therefore, either as to the disintegrating or transporting power of this mighty agent. When I stood upon the Mer de Glace I saw before me, in onegorge of the mountain, a continuous stretch of icy machinery fourteen miles in length by two to three in breadth, and several hundred feet in depth. The whole was in motion; and, whether we adopt as the principle of translation the mechanical pressure of Agassiz, or the hydraulic law of Forbes, the instrument of an incalculable carriage-power was there. And yet, upon the first glance, it shrank into a span, or appeared but as a small lake, as we viewed the glacier pouring down that deep gorge of Mont Blanc; a sheer depth of dark perpendicular rocks rising on its edges many thousand feet in height; several of the sharp-pointed Aiguilles, the Grandes Mullets, and above all, the Peak de Dru, unrivaled in symmetrical grandeur, penetrating still higher into the clear sky above. How many such glaciers are dispersed through that vast alpine chain; and how immense, upon any rule of calculation, have been the earthy and rocky materials which they have borne downward in the lapse of time!
Familiarized to such gigantic operations among his native Alps, M. Agassiz came to the conclusion that not only the bowlder drift of Switzerland, but nearly all the superficial accumulations of northern Europe, were to be ascribed to glacial action. In the straths and glens of Scotland he fancied a moraine in every talus of a mountain, and in every bar of a river. He saw the polishing of glaciers in the pass of Killiecrankie, on the sides of Ben Nevis, and the steep promontories of Morven. The parallel roads of Glenroy originated in the same cause. From the Mediterranean to the Arctic zone a polar climate universally prevailed, and the whole was covered with a mantle of ice; vast fields of ice, too, depending from the mountains penetrated into the adjacent valleys; the plains in succession were invaded, and erratic blocks were scattered in every direction; when at last, upon a change of temperature consequent upon other changes in the planetary relations of the earth, all these erosive influences were for a time increased, and the glacial power attained its maximum. Not only the upper and transverse furrows in the Alps but all the lower and great longitudinal valleys of the Cantons were the seats of glaciers during this period. Along the passes of the Rhine, the Rhone, the Drance, the Doire, the Arve, and the Isêre, the irrepressible tide of ice maintained its course, leaving portions of thedrift at different elevations, and dropping bowlders on the intermediate hills and on the more distant and loftier barriers of the Jura. Sir R. Murchison opposes all these speculations of Agassiz and others. The elevation of the alpine chain, of which there is abundant evidence in comparatively recent times, he regards as cotemporaneous with the translation of the bowlder-drift, and considers that during the sub-aqueous condition of northern Europe, the Alps and the Jura were from two to three thousand feet below their present altitude. He finds that the famous blocks of Monthey opposite Bex are composed exclusively of the granite of Mont Blanc—that they have been transported on ice-rafts through the gorge of St. Maurice to their present locality—and reasons with justice that had they formed part of a moraine the debris of all the intervening rocks, along the valley through which the glacier passed, must have been associated with them. None of the glaciers of the Alps, he thinks, could have been of the extent implied in the transport through their agency of the Jura blocks, nor have ever the upper longitudinal and flanking valleys around Mont Blanc been filled with general ice-streams. The materials, likewise, of true glacier moraines he conceives can be readily distinguished, on the one hand, from the more ancient alluvia, and, on the other, from tumultuous accumulations of gravel bowlders and far-transported erratic blocks. And, looking at the various causes which have affected the surface, Sir Roderick concludes, that all the chief difficulties of the bowlder-clay formation are removed, when it is admitted that frequent and vast changes of the land and waters have taken place since the distribution of large erratics—that a great northern glacial continent has subsided—that the bottom of the sea over Britain and the adjacent continent has been raised into dry land, while the Alps and Jura, formerly at lower levels, have been considerably and irregularly elevated.
The elevation of this stupendous chain of rocks, not by one but by a succession of upheavals and depressions ere they assumed their present position and grouping, is a point generally admitted, and not difficult to demonstrate. The Alps, for example, are folded all round with successive belts or zones of sedimentary matter, marking, as so many milestones at different points of altitude,the measure of increment attained during the intervals of their deposition. These belts contain each their own peculiar class of fossils which determine their relative ages. In succession, the several suites or families of rocks rest upon the inverted outcrop or inclined edges of the older groups. Thus the history of organic life upon the globe, the incoming of new races and the extinction of old ones, as contained in these deposits, becomes a scale of measurement of the elevations, disruptions, and ever-varying conditions of the inorganic crust, while in the inverted, dislocated state of the crust itself, we mark the several throes by which it was lifted above the waters. Not one of the fossiliferous beds enveloping the granitic and crystalline nucleus of the chain of the Alps but has been shifted out of its original horizontal position, and the shift of the subjacent having always preceded the deposition of the overlying formation, it follows that, in addition to the intumescence of the chain, there must have been a series of oscillatory and elevatory movements before attaining its final altitude. But after the consolidation of the whole rocky strata, and while the waters were still many thousands of feet in depth, the superficial accumulations were being deposited—the bowlder drift, and erratic blocks, either by icebergs or other causes, were floated into position—and it was not until every one of these traveled stones, fresh even now as when torn from the living rock, were quietly settled down into the bottom of the sea, that Mont Blanc had displayed a moiety of its massive outline, or towered to one-half of its present colossal grandeur. The elevation of Ben-Mac-Dhui dates from the era of the old red sandstone formation. Mont Blanc was invaded on all sides by a sea that received the latest of the tertiary deposits. Both were submerged during the cataclysm which produced the bowlder clay; but as no increment to its bulk was derived from this cause, Ben-Mac-Dhui falls geologically to be reckoned a completed, and therefore a far older, mountain than Mont Blanc, which had not attained its full altitude and bulk until the expiration of the Pleiocene age!
Such are the mighty agencies contemplated by the geologist in the various later changes which have affected the surface of our globe. The rill, the river, the torrent, the glacier, the earthquake,the volcano, are still in operation, but only as faint images of the enormous powers which in the more ancient times have been at work. That the earth has been repeatedly encroached upon by the waters every principle of his science goes to establish; but out of every convulsion he sees a better and more stable condition of things to have emerged. If the bowlder drift and the cold plastic clay formation point to a continuance of sunless, lifeless seasons, he forgets not, as the products of the period, that two-thirds of the soil of Great Britain and of the grain-bearing lands of the continent, have been derived from these accumulations—the industrial monuments of their invasion in every quarter of the world.