SUCCESSIVE PHASES OF GLACIAL ACTION IN THE ALPS, AND THEIR RELATION TO THE HUMAN PERIOD [Note 34].
According to the geological observations of M. Morlot, the following successive phases in the development of ice-action in the Alps are plainly recognisable:—
First. There was a period when the ice was in its greatest excess, when the glacier of the Rhone not only reached the Jura, but climbed to the height of 2015 feet above the Lake of Neufchatel, and 3450 feet above the sea, at which time the Alpine ice actually entered the French territory at some points, penetrating by certain gorges, as through the defile of the Fort de l'Ecluse, among others.
Second. To this succeeded a prolonged retreat of the great glaciers, when they evacuated not only the Jura and the low country between that chain and the Alps, but retired some way back into the Alpine valleys. M. Morlot supposes their diminution in volume to have accompanied a general subsidence of the country to the extent of at least 1000 feet. The geological formations of the second period consist of stratified masses of sand and gravel, called the "ancient alluvium" by MM. Necker and Favre, corresponding to the "older or lower diluvium" of some writers. Their origin is evidently due to the action of rivers, swollen by the melting of ice, by which the materials of parts of the old moraines were rearranged and stratified and left usually at considerable heights above the level of the present valley plains.
Third. The glaciers again advanced and became of gigantic dimensions, though they fell far short of those of the first period. That of the Rhone, for example, did not again reach the Jura, though it filled the Lake of Geneva and formed enormous moraines on its borders and in many parts of the valley between the Alps and Jura.
Fourth. A second retreat of the glaciers took place when they gradually shrank nearly into their present limits, accompanied by another accumulation of stratified gravels which form in many places a series of terraces above the level of the alluvial plains of the existing rivers.
In the gorge of the Dranse, near Thonon, M. Morlot discovered no less than three of these glacial formations in direct superposition, namely, at the bottom of the section, a mass of compact till or boulder-clay (Number 1) 12 feet thick, including striated boulders of Alpine limestone, and covered by regularly stratified ancient alluvium (Number 2) 150 feet thick, made up of rounded pebbles in horizontal beds. This mass is in its turn overlaid by a second formation (Number 3) of unstratified boulder clay, with erratic blocks and striated pebbles, which constituted the left lateral moraine of the great glacier of the Rhone when it advanced for the second time to the Lake of Geneva. At a short distance from the above section terraces (Number 4) composed of stratified alluvium are seen at the heights of 20, 50, 100, and 150 feet above the Lake of Geneva, which by their position can be shown to be posterior in date to the upper boulder-clay and therefore belong to the fourth period, or that of the last retreat of the great glaciers. In the deposits of this fourth period the remains of the mammoth have been discovered, as at Morges, for example, on the Lake of Geneva. The conical delta of the Tiniere, mentioned in Chapter 2 as containing at different depths monuments of the Roman as well as of the antecedent bronze and stone ages, is the work of alluvial deposition going on when the terrace of 50 feet was in progress. This modern delta is supposed by M. Morlot to have required 10,000 years for its accumulation. At the height of 150 feet above the lake, following up the course of the same torrent, we come to a more ancient delta, about ten times as large, which is therefore supposed to be the monument of about ten times as many centuries, or 100,000 years, all referable to the fourth period mentioned in the preceding page, or that which followed the last retreat of the great glaciers.*
(* Morlot, Terrain quaternaire du Bassin de Leman "Bulletin
de la Societe Vaudoise des Sciences Naturelles" Number 44.)
If the lower flattened cone of Tiniere be referred in great part to the age of the oldest lake-dwellings, the higher one might perhaps correspond with the Pleistocene period of St. Acheul, or the era when Man and the Elephas primigenius flourished together; but no human remains or works of art have as yet been found in deposits of this age or in any alluvium containing the bones of extinct mammalia in Switzerland.
Upon the whole, it is impossible not to be struck with an apparent correspondence in the succession of events of the glacial period of Switzerland and that of the British Isles before described. The time of the first Alpine glaciers of colossal dimensions, when that chain perhaps was several thousand feet higher than now, may have agreed with the first continental period when Scotland was invested with a universal crust of ice. The retreat of the first Alpine glaciers, caused partly by a lowering of that chain, may have been synchronous with the period of great submergence and floating ice in England. The second advance of the glaciers may have coincided in date with the re-elevation of the Alps, as well as of the Scotch and Welsh mountains; and lastly, the final retreat of the Swiss and Italian glaciers may have taken place when Man and the extinct mammalia were colonising the north-west of Europe and beginning to inhabit areas which had formed the bed of the glacial sea during the era of chief submergence.
But it must be confessed that in the present state of our knowledge these attempts to compare the chronological relations of the periods of upheaval and subsidence of areas so widely separated as are the mountains of Scandinavia, the British Isles, and the Alps, or the times of the advance and retreat of glaciers in those several regions and the greater or less intensity of cold, must be looked upon as very conjectural.
We may presume with more confidence that when the Alps were highest and the Alpine glaciers most developed, filling all the great lakes of northern Italy and loading the plains of Piedmont and Lombardy with ice, the waters of the Mediterranean were chilled and of a lower average temperature than now. Such a period of refrigeration is required by the conchologist to account for the prevalence of northern shells in the Sicilian seas about the close of the Pliocene or commencement of the Pleistocene period. For such shells as Cyprina islandica, Panopoea norvegica (= P. bivonae, Philippi), Leda pygmaea, Munst, and some others, enumerated among the fossils of the latest Tertiary formations of Sicily by Philippi and Edward Forbes, point unequivocally to a former more severe climate. Dr. Hooker also in his late journey to Syria (in the autumn of 1860) found the moraines of extinct glaciers, on which the whole of the ancient cedars of Lebanon grow, to descend 4000 feet below the summit of that chain. The temperature of Syria is now so much milder that there is no longer perpetual snow even on the summit of Lebanon, the height of which was ascertained to be 10,200 feet above the Mediterranean.*
(* Hooker, "Natural History Review" Number 5 January 1862
page 11.)
Such monuments of a cold climate in latitudes so far south as Syria and the north of Sicily, between 33 and 38 degrees north, may be confidently referred to an early part of the glacial period, or to times long anterior to those of Man and the extinct mammalia of Abbeville and Amiens.
