“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 11,000 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 moutonnées, 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 come 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.”
Whoever 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 1840 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 and there, as they died away, they left their terminal and lateral moraines still as well defined in some cases as moraines in lands where glaciers now exist. Frequently, too, masses of stone, that floated on the surface of the ice, were left perched upon the rounded roches moutonnées, in a manner somewhat puzzling to those who are not geologists.
“In short, they were let down upon the surface of these rocks so quietly and so softly, that there they will lie, until an earthquake shakes them down, or until the wasting of the rock on which they rest precipitates them to a lower level.”
It was the opinion of Agassiz, after visiting Scotland, that the Grampians had been covered by a vast thickness of ice, whence erratic blocks had been dispersed in all directions as from a centre; other geologists after a time adopted the opinion—Mr. Robert Chambers going so far as to maintain, in 1848, that Scotland had been at one time moulded by ice. Mr. T. F. Jamieson followed in the same track, adducing many new facts to prove that the Grampians once sent down glaciers in all directions towards the sea. “The glacial grooves,” he says, “radiate outward from the central heights towards all points of the compass, although they do not strictly conform to the actual shape and contour of the minor valleys and ridges.” But the most interesting part of Mr. Jamieson’s investigations is undoubtedly the ingenious manner in which he has worked out Agassiz’ assertion that Glenroy, whose remarkable “Parallel Roads” have puzzled so many investigators, was once the basin of a frozen lake.
Glenroy is one of the many romantic glens of Lochaber, at the head of the Spey, near to the Great Glen, or the valley of the Caledonian Canal, which stretches obliquely across the country in a northwesterly direction from Loch Linnhè to Loch Ness, leaving Loch Arkaig, Loch Aich, Glen Garry, and many a highland loch besides, on the left, and Glen Spean, in which Loch Treig, running due north and south, has its mouth, on the south. Glenroy opens into it from the north, while Glen Gluoy opens into the Great Glen opposite Loch Arkaig. Mr. Jamieson commenced his investigations at the mouth of Loch Arkaig, which is about a mile from the lake itself. Here he found the gneiss ground down as if by ice coming from the east. On the hill, north of the lake, the gneiss, though much worn and weathered, still exhibited well-marked striæ, directed up and down the valley. Other markings showed that the Glen Arkaig glacier not only blocked up Glen Gluoy, but the mouth of Glen Spean, which lies two miles or so north of it on the opposite side.
At Brackletter, on the south side of Glen Spean, near its junction with Glen Lochy, glacial scores pointing more nearly due west, but slightly inclining to the north, were observed, as if caused by the pressure of ice from Glen Lui. The south side of Glen Spean, from its mouth to Loch Treig, is bounded by lofty hills—an extension of Ben Nevis, the highest of these peaks exceeding 3,000 feet. Numerous gullies intersect their flanks, and the largest of these, Corry N’Eoin, presents a series of rocky amphitheatres, or rather large caldrons, whose walls have been ground down by long-continued glacial action: the quartz-veins are all shorn down to the level of the gneiss, and streaked with fine scratches, pointing down the hollows and far up the rocks on either side. During all these operations the great valley was probably filled up with ice, which would close Glen Gluoy and Glen Spean, and might also close the lowest of the lines in Glenroy. But how about the middle and upper lines?
A glacier crossing from Loch Treig, and protruding across Glen Spean, would cut off Glens Glaibu and Makoul, when the water in Glenroy could only escape over the Col into Strathspey, when the first level would be marked.