tunities which present for its application, and so well adapted does it appear to be where cleanliness, transparency, resistance to heat and chemical action, and comparative indestructibility are desiderata, that it would be idle to attempt to categorise them.

The invention is being taken up practically on the Continent, and no less in England. Messrs. Powell, of Whitefriars, are introducing it in their glass works, and two other firms in the north of England are doing the same. It is by no means improbable that its first introduction in practice in this country will be at the aquarium now in course of erection at Westminster, where it is intended to use it for the tanks.

There still remain some questions to be answered with regard to the phenomena exhibited by toughened glass; questions, however, which in no way affect the practical value of the mate.ial. Its peculiarities continue to form the subject of investigation, and as soon as any conclusions of value to science have been arrived at, they will be made known, so that the physical aspect of toughened glass may again be reverted to in these pages. In the meantime it may be mentioned, for the benefit of those who are prompted by something more than mere idle curiosity to look a little deeper into the matter, that specimens of toughened glass may be seen at the offices of Messrs. Abel Rey and Brothers, 29 Mincing Lane, City, those gentlemen being the agents of M. de la Bastie. It only remains to observe that the remarkable character and unique nature of M. de la Bastie's invention are such as to render it probable that he will not only materially benefit those of his own time, but will bequeath to posterity an invaluable legacy.

THE ICE AGE.-CLIMATE AND TIME.

BY ROBERT HUNT, F.R.S.

IT

T is exceedingly difficult for the untrained observer to realise the fact, that there was a period, extending over long centuries of time, during which the mountains of the British Isles were covered with perpetual snow, and the valleys deeply filled with fields of ice ;—when the temperate sea, which now, with its warm water, laves our shores, was a frozen mass, until far west, and south of Ireland, it broke up into icebergs, which, floating away into the Atlantic Ocean carried the arctic climate yet further southward. Yet the investigations of the geologist have elucidated no more satisfactory truth than this. That there was a period in the history of the Earth's mutations when an ice-sheet was spread over all northern continental Europe, forming an immense glacier in the Baltic, which flowed-as glaciers flow-into the North Sea, and found its outlet to the Atlantic by the English Channel;—when the mountain ranges of Scotland were buried in a frozen mass;when all northern England and Wales was swept by Scandinavian ice; and, when even the southern and south-western counties were within the influences of a constant temperature below that of frozen water. This was the period which is generally distinguished as the Glacial Epoch, but which a recent writer* has, with much terseness, termed the Great Ice Age. At what period of time did this arctic climate prevail? Evidence has lately been afforded, especially by the examination of the caves at Settle, that man existed during, or perhaps previous to this glacial age. In the history of man this time, to use Professor Ramsay's words, "though lost in the far backward abysm of time," yet in a geological sense so little preceded our own day, that the larger contours of hill and valley as they yet stand, were already in existence, and probably all the forms of mollusca now living even then inhabited the northern seas.†

James Geikie.

"The Old Glaciers of Switzerland and North Wales."

It is essential to the understanding of the theory dealing with those vast climatic changes, which the science of geology teaches us to believe it has discovered, by its inductive process of examining the organic remains preserved in, and the physical phenomena engraved on, our rocks, that the evidences collected should be succinctly given.

The evidences of predominance of a high temperature over a defined period, or within a well marked region, will be found preserved in the character of the flora and the fauna, which existed when the strata, in which their forms are fossilised, was in the progress of consolidation. As tropical life now differs from that which exists within the arctic circle, so through all time similar differences in organisation have been produced by the influences of a high temperature or a low one. We dismiss from consideration in this paper any influence which may be supposed to be due to purely terrestrial heat; the agencies with which we have to deal being sufficiently powerful to overcome, and, as it were, to mask the effects due, if any, to subterranean temperature. The palæontological evidences are numerous and decisive upon the question of the alternations of climate which have taken place in those long lapses of time, during which the surface of our planet has been slowly undergoing those changes, which have produced that succession of stratified rocks, which is the great stone book of Nature, bearing engraved in forcible language, the history of her grand mutations. With those we have only incidentally to deal until we arrive at the Post-tertiary period, when we glean, from the evidences of some great mechanical force which has left its markings, a knowledge of the fact that there ensued a period of great cold, which covered Northern Europe and our own islands with masses of moving ice.

It should be remembered that there can be no doubt but that several long epochs of great cold existed before that period, which is more especially to engage our attention. The fossil remains from which the geologist forms his estimate of the character of a climate during any geological period, are abundant during the epochs which may be distinguished as warm or tropical; but as a general rule those formations which geologists are inclined to believe indicate a cold condition of climate, are nearly devoid of fossil remains. The secular changes of climate which will be more especially noticed as occurring during, and since, the Great Ice Age, were the result of certain physical causes, recurring in obedience to fixed laws, which must have taken place during those vast periods of time which are lost in the infinite past.

Let us now examine-though the examination must necessarily be brief-some of the phenomena presented by existing

glaciers, and then see if similar indications preserved upon the rocks of the Tertiary period, do not lead to the conclusion that they are the result of like causes. The snows which fall upon the mountains of Switzerland are pressed into masses of ice, and these, necessarily in obedience to the force of gravitation, have a tendency to move down their sloping sides.

For a considerable period a discussion was carried on, not always in the true philosophical spirit, as to the physical state of the frozen mass of the moving glacier. One hypothesis regarding ice as a plastic material, moving by virtue of that plasticity, as pitch moves-the other supposing the ice to be melted by the enormous pressure to which it is subjected; but immediately recongealing, or as it is expressed, regelating into a homogeneous solid, and thus maintaining its onward motion. We need not here examine the delicate differences between those two views. Since we now know that solid iron, cold, may be pressed by a sufficient exercise of mechanical force through small orifices-flowing indeed as a fluid flows-there surely can be no difficulty in conceiving how "the glacier's cold resistless mass" may be forced onward, day by day, by the enormous mechanical power which is ever pressing it in the rear. The writings of Agassiz, and of Professor James Forbes, have rendered familiar the fact that the moving glacier, by its enormous pressure, rounds off the asperities of the rocks, and covers their surfaces with striations. By a steady grinding process all the original angles are worn off, and the whole assumes a mammilated appearance; the surfaces being polished, grooved and striated by the imprisoned stones and finer débris that lie between the solid mass, of the slowly progressing ice, and the rocky floor over which it passes. This moving frozen river of ice carries with it every thing that falls upon it, from the smaller débris, to the huge blocks of rock, which have been broken out of the mountains-roches moutonnées and blocs perchés-and these are transported by it, to be left eventually, as the ice melts by advancing to a warmer region, to mark the course taken by the glacier. Such are the results of the known movements of glacial ice. When those frozen masses advance into the sea-as they do on the coasts of Greenland-they are gradually broken up into icebergs, which float far away towards the south, eventually melting under the influence of warmer waters, and dropping on the sea bottoms any boulders, or smaller masses of rock, which they may have borne from the land upon which they originated.

These fragments of the disintegrated rocks are left as unmistakable indications of the channels along which the glaciers moved, or of the regions over which the gliding ice of the land, or the floating iceberg of the sea, bore its weighty spoil. This

is proved most conclusively by the effects which are seen to result from the fluctuations in the dimensions of existing glaciers. Professor Ramsay* informs us that, since the year 1767, the glacier of La Brenva rose 300 feet above its present level, and again declined, and the terminal moraines of the Rhone glacier arranged concentrically, one within another, bear witness to its recent gradual diminutions. The great Gorner glacier of Monte Rosa is even now steadily advancing, and is said, within the memory of men not old, to have already swallowed up forty châlets and a considerable tract of meadow land. He continues to remark, that such historical variations in the magnitude of glaciers are trifling, compared with their wonderful extensions in prehistoric times. In the Alps we find numerous instances of the former presence of glaciers where none now exist. “So startling indeed are these revelations, that for a time the observer scarcely dares to admit to himself the justness of his conclusions, when he finds in striations, moraines, roches moutonnées and blocs perchés, unequivocal marks of the former extension of an existing glacier, more than a long day's march beyond its present termination; and further, that its actual surface of to-day is even 2,000 feet and more beneath its ancient level."

The careful student of these striking indications will, as he ascends the mountain slopes, observe rounded slopes and striated contours to considerable heights above him, plainly marking the breadth and height of the glacier at early periods of its history, and in the uppermost regions the serrated and weatherworn crags that form the lips of the valleys, now almost bare of snow, still define the upward limits where the solid flowing ice in old times ceased to grind the rocks. Beyond this we know that all glaciers deepen their beds by erosion. The enormous weight of the mass of ice moving with irresistible power must tend to grind the surface upon which it moves, and thus cut out channels, and even scoop out lakes from its bed. Indeed, the general origin of lakes has been referred by Professor Ramsay to glacial action, and his hypothesis is supported by evidences which appear to be almost conclusive.

The evidences marked upon the rocks of the globe are the only records which remain of the influences to which they have been subjected in past ages; and, it is only by a proper understanding of the events embodied in these "sermons in stones" that the geologist can hope to give any real value to his deductions. It has been well said by Mr. Croll, in his remarkable book "Climate and Time":—

"No amount of description, arrangement and classification, however perfect or accurate, of the facts which come under the

"The Old Glaciers of Switzerland and North Wales."