449

GLACIAL PERIOD.

of ancient glaciers far distant from their existing limits. Heaps of debris, of all sizes, comprehending blocks with sharp-pointed angles, are found in the Swiss plains and valleys. Blocs perches (Perched blocks), as in Pl. XXXI., are often seen perched upon points of the Alps situated far above existing glaciers, or dispersed over the plain which separates the Alps from the Jura, or even preserving an in-

Fig. 197.— Transported blocks.

credible equilibrium, when their great mass is taken into consideration, at considerable heights on the eastern flank of this chain of mountains. It is by the aid of these indications that the geologist has been able to trace to extremely remote distances signs of the former existence of the ancient glaciers of the Alps, to follow them in their course, and fix their point of origin, and where they terminated. Thus the humble Mount Sion, a gently-swelling hill situated to the north of Geneva, was the point at which three great ancient glaciers had their confluence — the glacier of the Rhone, which filled all the basin of Lake Leman, or Lake of Geneva; that of the Is^re, which issued from the Annecy and Bourget Lakes; and that of the Arve, which had its source in the valley of Chamounix, all converged at this point. According to M. G. de Mortillet, who has carefully studied this geological question, the extent and situation of these ancient glaciers of the Alps were as follows:— Upon its northern flank the glacier of the Rhine occupied all the basin of Lake Constance, and extended to the borders of Germany; that of the Linth, which was arrested at the extremity of the Lake of Zurich — this city is built upon its terminal moraine — that of the Reus^ which covered the lake of the four cantons with blocks torn from the peaks of Saint-Gothard; — that of the Aar, the last moraines of which crown the hills in the environs of Berne;— those of the Arve and the Isere, which, as we have said, debouched from Lake Annecy and Lake Bourget respectively;— tiat of the Rhone, the most imf)ortant of alL It is this D D

450

THE WORLD BEFORE THE DELUGE. glacier which has deposited upon the flanks of the Jura, at the height of 3,400 feet above the level of the sea, the great erratic blocks already described. This mighty glacier of the Rhône had its origin in all the lateral valleys formed by the two parallel chains of the Valais. It filled all the Valais, and extended into the plain, lying between the Alps and the Jura, from Fort de L’Écluse, near the fall of the Rhône, up to the neighbourhood of Aarau.

The fragments of rocks transported by the ice-sea which occupied all the Swiss plain follow, in northerly direction, the course of the valley of the Rhine. On the other hand, the glacier of the Rhône, after reaching the plain of Switzerland, turned off obliquely towards the south, received the glacier of the Arve, then that of the Isère, passed between the Jura and the mountains of the Grande-Chartreuse, spread over La Bresse, then nearly all Dauphiny, and terminated in the neighbourhood of Lyons.

Upon the southern flank of the Alps, the ancient glaciers, according to M. de Mortillet’s map, occupied all the great valleys from that of the Dora, on the west, to that of the Tagliamento, on the east. “The glacier of the Dora,” says de Mortillet, whose text we greatly abridge, ‘‘debouched into the valley of the Po, close to Turin. That of the Dora-Baltéa entered the plain of Ivréa, where it has left a magnificent semicircle of hills, which formed its terminal moraine. That of the Toce discharged itself into Lake Maggiore, against the glacier of the Tessin, and then threw itself into the valley of Lake Orta, at the southern extremity of which its terminal moraines were situated. That of the Tessin filled the basin of Lake Maggiore, and established itself between Lugano and Varése. That of the Adda filled the basin of Lake Como, and established itself between Mendrizio and Lecco, thus describing a vast semicircle. That of the Oglio terminated a little beyond Lake Iseo. That of the Adige, finding no passage through the narrow valley of Roveredo, where the valley became very narrow, took another course, and filled the immense valley of the Lake of Garda. At Novi it has left a magnificent moraine, of which Dante speaks in his ‘Inferno.’ That of the Brenta extended over the plain of that commune. The Drave and the Tagliamento had also their glaciers. Finally, glaciers occupied all the valleys of the Austrian and Bavarian Alps.” *

Similar traces of the existence of ancient glaciers occur in many other European countries. In the Pyrenees, in Corsica, the Vosges, the Jura, &c., extensive ranges of country have been covered, in

“Carte des Anciens Glaciers des Alpes,” pp. 8—10. (1860.)

geological times, by these vast plains of ice. The glacier of the Moselle was the most considerable of the glaciers of the Vosges, receiving numerous affluents; its lowest frontal moraine, which is situated below Remiremont, could not be less than a mile and a quarter in length. But the phenomenon of the glacial extension which we have examined in the Alps was not confined to Central Europe. The same traces of their ancient existence are observed in all the north of Europe, in Russia, Iceland, Norway, Prussia, the British Islands, part of Germany, in the north, and even in some parts of the south, of Spain. In England, erratic blocks of granite are found which were derived from the mountains of Norway. It is evident that these blocks were borne by a glacier which extended from the north pole to England. In this manner they crossed the Baltic and the North Seas. In Prussia similar traces are observable.

Thus, during the Quaternary epoch, glaciers which are now limited to the Polar regions, or to mountainous countries of considerable altitude, extended very far beyond their present known limits; and, taken in connection with the deluge of the north, and the vast amount of organic life which they destroyed, they form, perhaps, the most striking and mysterious of all geological phenomena.

M. Edouard Collomb, to whom we owe much of our knowledge of ancient glaciers, furnishes the following note explanatory of a map of Ancient Glaciers which he has prepared:— " The area occupied by the ancient Quaternary glaciers may be divided into two orographical regions:— i. The region of the north, from lat. 52° or 55^ up to the North Pole. 2. The region of Central Europe and part of the south. " The region of the north which has been covered by the ancient glaciers comprehends all the Scandinavian peninsula, Sweden, Norway, and a part of Western Russia, extending from the Niemen on the north in a curve which passed near the sources of the Dnieper and the Volga, and thence took a direction towards the shores of the glacial ocean. This region comprehends Iceland, Scotland, Ireland, the isles dependent on them, and, finally, a great part of England. " This region is bounded, on all its sides, by a wide zone from 2° to 5^* in breadth, over which is recognised the existence of erratic blocks of the north: it includes the middle region of Russia in Europe, Poland, a part of Prussia, and Denmark; losing itself in Holland on the Zuider Zee, it cut into the northern part of England, and we find a shred of it in France, upon the borders of the Cotentin. " The ancient glaciers of Central Europe consisted, first, of the DD 2

grand masses of the Alps. Stretching to the west and to the north, they extended to the valley of the Rhone as far as Lyons, then crossing the summit-level of the Jura, they passed near Basle, covering Lake Constance, and stretching beyond into Bavaria and Austria. Upon the southern slopes of the Alps, they turned round the summit of the Adriatic, passed near to Udinet, covered Peschiera, Solferino, Como, Varese, and Ivrea, extended to near Turin, and terminated in the valley of the Stura, near the Col de Tenda.

"In the Pyrenees, the ancient glaciers have occupied all the principal valleys of this chain, both on the French and Spanish sides, especially the valleys of the centre, which comprehend those of Luchon, Aude, Bareges, Cauterets, and Ossun. In the Cantabrian chain, an extension of the Pyrenees, the existence of ancient glaciers has also been recognised. " In the Vosges and the Black Forest they covered all the southern parts of these mountains. In the Vosges, the principal traces^ are found in the valleys of Saint- Amarin, Giromagny, Munster, the Moselle, &c. " In the Carpathians and the Caucasus the existence of ancient glaciers of great extent has also been observed. " In the Sierra Nevada, in the south of Spain, mountains upwards of 1 1, GOO feet high, the valleys which descend from the Picacho de Veleta and Mulhacen have been covered with ancient glaciers during

the Quaternary epoch." There is no reason to doubt that at this epoch all the British islands, at least all north of the Thames, were covered by glaciers in their higher parts. " Those," says Professor Ramsay, "who know the Highlands of Scotland, will remember that, though the weather has had a powerful influence upon them, rendering them in places rugged, jagged, and cliffy, yet, notwithstanding, their general outlines are often remarkably rounded and flowing; and when the valleys are examined in detail, you find in their bottoms and on the sides of the hills that the mammillated structure prevails. This rounded form is known, by those who study glaciers, by the name of roches moiito?inecs, given to them by the Swiss writers. These mammillated forms are exceedingly common in many British valleys, and not only so, but the very same kind of grooving and striation, so characteristic of the rocks in the Swiss valleys, also marks those of the Highlands of Scotland, of Cumberland, and Wales. Considering all these things, geologists, led by Agassiz some five or six and twenty years ago, have by degrees corne to the conclusion, that a very large part of our island was, during the glacial period, covered, or nearly covered, with a thick

coating of ice in the same way that the north of Greenland is at present; and that by the long-continued grinding power of a great glacier, or set of glaciers nearly universal over the northern half of our country, and the high ground of Wales, the whole surface became moulded by ice." AVhoever traverses England, observing its features with attention, will remark in certain places traces of the action of ice in this era. Some of the mountains present on one side a naked rock, and on the other a gentle slope, smiling and verdant, giving a character more or less abrupt, bold, and striking, to the landscape. Considerable portions of dry land were formerly covered by a bluish clay, which contained many fragments of rock or " boulders " torn from the old Cumbrian mountains; from the Pennine chain; from the moraines of the north of England; and from the Chalk hills — hence called "boulder"' clay — present themselves here and there, broken, worn, and ground up by the action of water and ice. These erratic blocks

or " boulders '' have clearly been detached from the parent rock by violence, and often transported to considerable distances. They have been carried, not only across plains, but over the tops of mountains ] some of them being found 130 miles from the parent rocks. We even find, as already hinted, some rocks of which no prototypes have been found nearer than Norway. There is, then, little room for doubting the fact of an extensive system of glaciers having covered the land, although the proofs have only been gathered laboriously and by slow degrees in a long series of years. In 1 840 Agassiz visited Scotland, and his eye, accustomed to glaciers in his native mountains, speedily detected their signs. Dr. Buckland became a zealous advocate of the same views. North Wales was soon recognised as an independent centre of a system which radiated from lofty Snowdon, through seven valleys, carrying with them large stones and grooving the rocks in their passage. In the pass of Llanberis there are all the common proofs of the valley having been filled with glacier ice. ■" When the country was under water," says Professor Ramsay, " the drift was deposited which more or less filled up many of the Welsh valleys. When the land had risen again to a considerable height, the glaciers increased in size: although they never reached the immense magnitude which they attained in the earlier portion of the icy epoch. Still they became so large that such a valley as the Pass of Llanberis was a second time occupied by ice, which ploughed out the drift that more or less covered the valley. By degrees, however, as we approach nearer our own days, the climate slowly ameliorated, and the glaciers began to decline, till, growing less and less, they crept up and up; and here

Page 68 of 79