The Glaciers of Great Britain

A Vast number of my readers would be inclined to stare at anybody who began to talk of the glaciers of Great Britain, and would perhaps set him down as a person of neglected education, but they would change their opinion if taken to see the actual places where these things occurred, and the unmistakeable marks that they have left behind.

Tourists who fancy that the Alps or the Dovre Feld are the only European localities, which have ever been the centre of perpetual snow, should go and examine the traces of ice so frequently to be found in the mountain ranges of North Wales or Cumberland, and they will be able to compare the signs of the mighty past with the operations of Nature going on at this very time.

What makes the inquiry the more interesting, is the fact that all these events happened at a geological period, very nearly allied to our present era (when the outlines of the country had assumed much the same shape as they now present), and that to them are due, to a great extent, the beautiful variety of hill and dale, and the different kinds of soil for the support and nourishment of the vegetable kingdom.

Before we go back to the past, let us take a brief summary of the present, and inquire into the movements and effects of glaciers as now existing in the Alps. Notwithstanding the large surface covered in those regions by snow and ice, it is clear that many of the glaciers have considerably declined in size. Some have risen, indeed, and swelled out, but as a rule they have receded. Although apparently bound immoveably in the fetters of frost, no glacier is ever permanent or stationary; but, on the contrary, slowly but surely moves on with an irresistible pressure that carries everything before it, and it is almost incredible what enormous rocks are rolled forward as far as its influence extends.

Certain effects are thus caused, which show the observant savan the indubitable marks of ice, plainly proving that a glacier has, at one time or other, filled the bottom of the mountain ravine which he is exploring.

The most prominent and common of these signs are long lines of stones which settle on the sides of the glacier, having been detached from the surrounding rocks by the action of the frost, lightning, avalanches, &c.

These are called lateral “moraines,” in contradistinction to other heaps found at the end of the glaciers, which are “terminal moraines.” These last, however, by being constantly propelled forward and ground, down against each other, are in a more fragmentary state than those on the sides, and at length accumulate in a great mound which, nevertheless, does not always remain as an after-mark of the former presence of a glacier, and for this reason.

By the accumulation, a dam is formed across the valley, acting as a barrier to the lake-waters, generally found in an old glacier basin, but which in floods and storms, frequently burst through the moraine mound, carrying death and destruction in their course down the vale. As the stones which compose the moraines are carried forward, they rub up against each other, causing great wearing of the surface, and also scrape deeply and heavily against the rock over which the glacier is flowing; and such is the tremendous pressure to which they are subject, that not only are the surfaces of the rock often polished by the friction, but “striated,” as geologists term it, i. e., marked by straight lines, as though done by a machine, whilst in many cases deep grooves are regularly furrowed in.

Sometimes, also, a projecting eminence is smoothed and worn into a round shape, somewhat like a sheep lying down, from whence these rocks are termed “roches moutonnfies.” There is another still more curious appearance of frequent occurrence, when a glacier happens to have surrounded a peak or pinnacle of mountain, and lodges a ring of stones all round it. After a time the ice melts, and the stones, which are called “perched blocks,” are seen grouped at the top of the peak in the most fantastic situations, as though a number of Titans had been amusing themselves with a Brobdingnag game at marbles.

Now, these peculiar marks, the moraines, striatums, groovings, “roches moutonnees,” &c, are to be observed in the Alps in many situations, where glaciers do not now exist, attesting their former presence; and many skilful observers, such as Forbes, Tyndall and Ramsay, were enabled to make accurate maps of their course, extent, and depth, by noting these various signs.

But, perhaps, my readers will be inclined to say, What has all this to do with Great Britain? Simply that the same marks which are to be seen in the Alps may be found on the Grampians, the hills of Cumberland, and the ranges of Snowdon. The latter mountain has been shown by Professor Ramsay to have been the centre of six glaciers that flowed from the direction of the peak down as many valleys that radiate from the summit; and in Cwm-Glas in particular, which runs down towards the pass of Llanberris, there is an exceedingly large moraine heap, which, however, since the disappearance of the glacier, has been a good deal cut away by the stream that drains the Pass.

It is evident from the position of the boulders — (a geological term for all these stones which have been carried away) — and the striae on the face of the rocks, that this mass of ice descended Cwm-Glas, and with others aided to form the great glacier of Llanberris, the grooving from which Mr. Ramsay has traced in forty six places on the hills on each side of the lake, at such heights that he has been enabled to calculate the thickness of the ice that filled the valley, at about 1200 feet.

Not only Snowdon itself, but the whole of the mountain country between Bangor, Conway, and Capel Curig bears the traces of either glaciers or icebergs, which latter have caused in the northern counties of England the still more striking and wide-spread appearances, known to geologists by the name of drift. Not only the north of Great Britain, but also of Europe and North America, presents this feature, which for a long time puzzled the scientific world.

Quantities of loose rocks, of all sorts and sizes, cover the ground to such an extent that it received the name of boulder, or drift formation, and in many places, is locally called “till,” the peculiarity of it being that the stones which compose it do not belong to the same formation as that of the locality in which they are found; but are probably hundreds of miles from the spot where they were originally “in situ.”

Mr. Binney has found in the till around Manchester fragments of granite, slates, and Silurian rocks, mountain limestone, coal measures, and new red sandstone. Now, as soon as these phenomena were found to be so general, the question arose, How did they come there? Many put them down to the deluge; but this theory involved them in such difficulties in reconciling geology to religion, that it was soon abandoned. It is not necessary to detail all the speculations and hypotheses on the subject — suffice it to say that the one generally accepted is that of the glacial era — an era of intense cold, such as man has probably never known, when the whole earth lay buried in perpetual winter.

From the north issued tremendous icebergs, which overran all North Europe and America, and the extreme cold thus produced gave birth at the same time to the glaciers of the Grampians, the Lake Mountains, and Snowdon. Now it is well known that icebergs at the present day, break off from the mainland, and are carried by currents for many miles, bearing with them out to sea (like the glaciers causing the moraines), numbers of stones and rocks, which when the berg melts, are gently deposited at the bottom, and even now the western Atlantic is becoming sown with earth by this means.

In the same way, the icebergs of Scandinavia brought fragments of the old rocks, and scattered them over Russia, Prussia, and the coast of England, as far south as Essex; while the greatest portion of the till which is found in the more centrally northern counties, is supposed to have been brought in the same way from Cumberland, Scotland, and Wales. In Lancashire and Cheshire they are in prodigious numbers, a fact which Mr. Binney is inclined to attribute to a glacier extending thither from the Lake district.

In North America, Professor Ramsay has well shown that the great Laurentian chain of mountains on the north side of the St. Lawrence, exhibits for an extent of 1500 miles, unequivocal signs of glacial action, being often striated, and showing “roches moutonnees,” while the low country on the south side of the river is covered with boulders and drift.

An interesting question now occurs, as to the probable shape and features of England in those times. The outlines and great contours of the land are supposed to have been, to a certain extent, pretty much the same as they are now, with this important difference, however, that it was nearly all under water.

Sinkings and elevations of a country, or even of a whole continent, are of common occurrence in geological history, and offer explanations of many a difficulty; and it is quite evident that at the time of the glacial epoch, Great Britain consisted of only a few islands, the tops of which appeared above water, while over the remainder icebergs were carrying their freight of boulders. Gradually, however, a powerful, though slow elevating force was at work, uplifting the country, and ever and anon stopping for a while; and as a proof of these things, it may be stated that seashells of an Arctic type (that is, of a type now existing in the Arctic oceans), have been found at the top of Moel Tryfan, near Snowdon, at a height of 1300 feet above the sea.

All through Britain and Ireland the drift may be seen on the flanks of the mountains, and in North Wales to a height of 2300 feet! and not only this, but it is found arranged in terraces, showing the periods of rest in the elevating forces. In many parts of England, such as Worcester, Shrewsbury, and the Vale of Gloucester, shells have been found, indicating the lines of the drift. The reasons of the glacial climate are not quite so clear as the results, but they arose no doubt from enormous changes in the relative amount of land and water, which, it is well known, exercises a vast influence over the temperature of climate.

The eastern side of any large continent is always more extreme in the heat and cold of summer and winter than that of the west, and from observations made by Humboldt, and many eminent English geologists, it is considered not improbable that Britain formed the eastern side of America, what is now sunk under the Atlantic having been dry land. England would, in that case, have possessed a climate somewhat resembling Labrador. The Gulf stream is the principal agent in causing a mild temperature in this country; but were the Isthmus of Panama to be submerged, and the Gulf stream to flow into the Pacific instead of its present course, there is no telling how far our temperature might be reduced.

It may occur to the reader to inquire, what is the length of time that has elapsed since the glacial sea rolled over Europe? A very rough guess is the nearest approximation that we can ever arrive at, and such has been done by Sir Charles Lyell, who from certain experiments and observations made on the falls of Niagara, suggested that 35,000 years at least had been consumed in the erosion or wearing away of the rocky bed by the action of the water, and from geological appearances it seems that the Falls commenced at the close of the drift period.

After all, though we cannot but admire and wonder at the abstract reasoning of these masters in geological science, we must accept such calculations with great caution, remembering how infinite (to man’s ideas), is all geological time — only to be compared to the distances between the earth and the fixed stars, about which we so often speak, but which we cannot realise.

What has been the ultimate end of this long continued region of winter? It was a season of desolation and sterility, in order that the future country might be made more flourishing, for it is to the “drift” that a great portion of the soil owes its formation, mixture, and arrangement, and the earth finally rendered complete for the reception of God’s highest work — Man.

September 1859


 

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