As an approximation to the period when this district was last subject to volcanic action, it may be noticed that the craters of Auvergne and the Cantal had all ceased to emit fire or were just expiring, when those of Etna and Vesuvius began their operations. From whatever cause, it would appear that the incandescent elements had here parted with their caloric or had shifted their position, and that new vents were opened for them in the basin of the Mediterranean. These latter volcanoes may have been in activity before the historical epoch, although the evidence must still be regarded as inconclusive, and the violent efforts to fasten a collision upon revelation have utterly failed. But in Auvergne, on the contrary, little doubt exists of the priority of all the volcanic emissions to the human epoch. When Cæsar encamped among these narrow defiles, his Commentary is silent as to any eruptions save the irruption of his own legions. The inhabitants, as now, were cultivating the vine or peacefully engaged in rural occupations, as little dreaming of any disturbances from the interior, as they were unprepared to resist the torrent of mail-clad warriors that poured through their valleys and devastated their fields. The poet Sidonius Apollinaris had his residence on the borders of Lake Aidat, but he sung not of the “sublime” in these upthroes of his native province. Nevertheless, an immense degree of historic interest must ever attach to these volcanic rocks, inasmuch as they are infinitely modern when compared with the primary and secondary formations, the granites and the traps of Britain. They keep continually, too, before our eyes the fact of a succession of igneous operations, and remind us that plutonic agencies have prevailed through all time, and over regions which have only recently been liberated from their ravages; that at any moment, and at any place, they may again burst forth, when islands will be raised, continents submerged, the fertile plain laid waste, and lakes, estuaries, and seas converted into dry land.
Nor are there evidences wanting, in existing volcanoes, of the intensity of the fires which still glow within the interior of our earth. There are at present more than two hundred volcanoes in active operation; these are not confined to any particular zone, but are distributed like those of the older families through the different quarters of the world. The greater centers of action are situated in the mountain-ranges of South America, along the western coast of North America, and in the numerous islands of the Southern Pacific; but at the same time there is scarcely a portion of the earth’s crust that is not subjected to the shock of volcanic influence and the movement of earthquakes. There are two theories by which all volcanic phenomena are attempted to be explained. The more prevailing one among geologists is that which connects them with one great source of central heat—interior lakes of molten stone—the residue of that incandescent condition in which the globe originally appeared, and out of which the primary crystalline strata were formed. The other mode of explanation is that which supposes the internal heat to be the result of chemical and galvanic action among the materials composing the earth’s crust. The metallic and earthy bases, upon contact with water, everywhere transmitted through fissures and apertures on the surface, burn, melt, and are converted into lavaform matter, and which acting again as fuel, serve to fuse the rocks among which they occur. Hence various gases will be generated sufficient to occasion much local disturbance; though certainly not upon a scale to correspond with the magnitude, universality, and perpetuity of those changes that have resulted in the igneous products of the primary, secondary, or even tertiary formations.
But whatever be the source or cause, the heat and the elements of heat have been in constant activity, volcanoes and earthquakes, like the hurricane and disease, subserving important necessary purposes in the economy of nature. Humboldt was the first to remark the linear distribution of volcanic domes, which he considered as vents placed along the edge of vast fissures, communicating with reservoirs of igneous matter, and extending across whole continents. Lyell, considering that the earthquake and the volcano are probably the effects of the same subterranean process, and that the subterranean movements are least violent in the immediate proximity of volcanic vents, observes, “that if the fused matter has failed several times to reach the surface, the consolidation of the lava first raised and congealed will strengthen the earth’s crust, and become an additional obstacle to the protrusion of other fused matter during subsequent convulsions.” Thus, needful in all past time, these igneous phenomena are needful still—in supplying and indurating new lands—in repairing the waste and continual encroachments of the sea—in keeping up a salutary degree of heat over the earth’s crust, and thereby perhaps essential toward maintaining the necessary volume of the earth’s bulk. Nor will the fires within have fulfilled their law and purpose of inclosure until the ordinance of Heaven in its creation be completed, when the earth and the works therein shall be burnt up.
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 the principal 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.