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by Dean Trench in his valuable work on the Miracles of our Lord.*
We would, in conclusion, once more draw attention to the great dearth of trustworthy information on the subject of the Natural History of Palestine. Of the geology of that country we know next to nothing, so that here is a wide field full of fruitful promise. What fish swim in the Jordan and in the Sea of Galilee? How far is the ichthyological fauna of Palestine identical with that of the fresh waters of Syria, described by Heckel (Süsswasser-Fische Syriens, in Abbild. u. Beschrieb. neuer u. seltener Thiere u. Pfanz. in Syrien,' &c., von Kotscky Fenzl. Heckel u. Redtenbacher, 1843)? We recommend these remarks especially to the consideration of Mr. Tristram, to whom we are already much indebted for his contributions to our knowledge of the ornithology of the Holy Land; and we trust he will forgive us if, in the cause of science, we venture to express a hope that his health will shortly again require a little change of air, and that Palestine will be the country visited.
ART. III.-1. Voyages dans les Alpes, précédés d'un Essai sur
l'Histoire Naturelle des Environs de Genève. Par M. de Saussure, Professeur emérite de Philosophie dans l'Académie de Genève. Vols. I., II., III., IV. Published in 1779, 1786,
1796. Neuchâtel. 2. Théorie des Glaciers de la Savoie. Par M. le Chanoine Rendu,
Chevalier du Mérite Civil. From the Mémoires de la Société
Royale Académique de Savoie.' Vol. X. 1841. 3. Essai sur les Glaciers, et le Terrain Erratique du bassin du
Rhone. Par M. Charpentier, Directeur des Mines du Canton
de Vaud. 1841. 4. Système Glaciaire, ou Recherches sur les Glaciers. Par MM.
Agassiz, Guyot, et Desor. 1847. 5. Travels through the Alps of Savoy; with Observations on the
Phenomena of Glaciers. By Professor James D. Forbes, F.R.S.,
F.G.S., &c. Edinburgh. 1843. 6. Occasional Papers on the Theory of Glaciers. By Professor
James D. Forbes. 1859. 7. Various Memoirs on Glacial Theory, in the Transactions of the
Royal Society, 1862, and of the Cambridge Phil. Society. By W. Hopkins, M.A., F.R.S., F.G.S.
* 3rd edit., p. 433.
8. The Glaciers of the Alps. By Dr. Tyndall, F.R.S., Professor
of Natural History in the Royal Institution of Great Britain,
and in the Government School of Mines. 1860. W HOEVER has been in the habit of contemplating the
V beauties of the works of nature or of art must necessarily feel the importance of regarding them from the best points of view. In the grander scenes of nature, for instance, when seen from an ill-chosen point, the mountain may appear too dominant, the expanse of water too large, or the distance too insignificant; and, however grand or beautiful each object may be individually, the general effect may be unsatisfactory to the cultivated eye. We must seek for that point in which every object appears in its due proportion, and helps to produce that general harmony in which the highest beauty of nature and art essentially consists. And so it is with science. In the earlier periods of the development of any complicated branch of knowledge, its several parts will frequently appear more or less disjointed, out of keeping with each other, and wanting in that more perfect harmony which is the surest test of truth in science, as well as the highest result of the beauties of external nature. Still Time, the great arbiter in such matters, gradually asserts his influence, and a period arrives at which we may be enabled to form at least a fair approximate estimate of the relative merits of the various conclusions in an advancing science. Such appears to us to be at present the state of Glacial Science. We have hitherto abstained from taking much part in the discussion of the subject, notwithstanding the popular and scientific interest which has been justly attached to it, not merely on its own account, but also on account of its important bearings on certain conclusions of geologists. We believe that premature criticism has been bestowed upon it; and if we now present a view of it somewhat different from those which have hitherto been more frequently advocated, we trust that we shall be regarded as doing so, not from partiality or prejudice, but on account of the present more perfect development and altered phase of the science.
Most of our readers will probably have formed some more or less distinct conception of a glacier; but we think it advisable to preface our examination of the various views which have been put forward on the subject, by a very general and brief description of those curious masses of ice and of the mode of their formation. If a mountain be of sufficient elevation, the temperature in its higher portions may be always below the freezing temperature, in which case the aqueous vapours which rise in the atmosphere above the summit of such a mountain, and subsequently fall upon it, must usually assume the form of snow; and thus it is that continual additions of snow are supplied to these elevated regions. At the same time there are several causes which restrict this increase within determinate limits. Thus the high winds which frequently play about the tops of the mountains are often the means of scattering thence a certain quantity of snow, and depositing it at lower levels. The frequency of avalanches, also, in the higher regions is well known to the mountain traveller; and another cause for the diminution of these elevated masses of snow is to be found in the radiating heat of the sun, which thaws a certain superficial portion of the mass on which it falls, and thus affords an effective aid in counteracting the tendency to indefinite accumulation.
The water produced by this melting sinks into the porous mass of snow; and, since the temperature of the mass must necessarily, at the elevations we are here contemplating, be less than that of freezing, the percolating water will be, at least, partially frozen, and will constantly tend to convert the mass of snow into ice, and thus to give it greater firmness and consistency. Pressure and certain other causes may also assist in the work of consolidation, till at length the mass is found to assume its final character of transparent solid ice.
In the higher regions of a mountainous chain there are usually many precipitous peaks and ridges with deep intervening continuous valleys, or more circumscribed circus-like hollows. The great majority of these have openings by means of which their drainage is more or less perfectly effected. If the ridge of a snow-mountain have this character, it is manifest that the snow which covers it will always tend to accumulate in the valleys, as being more sheltered than the neighbouring heights. Now it is found by observation that the masses of ice and snow thus accumulated do not remain quietly at rest, but creep slowly forth from their original cradles through the drainage valleys above mentioned. These latter valleys are in general nearly in the lines of quickest descent on the mountain side, and it is along them that the glacial masses of ice and snow descend from the higher regions in which they originate. Here, then, we have another and effective cause in constant action to limit the accumulation of snow and ice on summits of mountains on which they are formed, and to establish the equilibrium between the growth of the whole glacial mass in the higher and colder regions and its waste in the warmer regions below. When a range of mountains is so high that its summits are
thing files and the scenter of lethe uppehe meltinet
covered with perpetual snow, the line above which the snow never disappears is called the snow-line. The summer temperature at any point of it never exceeds 32° (Fahr.). The elongated portions of the general glacial mass which protrude below this line in valleys descending along the sides of the mountain, as above intimated, are more especially termed glaciers. The larger of them (those of the first order or primary glaciers) vary from four or five to ten or twelve miles in length. These are not essential limits, but they hold approximately in the Alpine glaciers, with which we are more familiarly acquainted than with any other. It is on glaciers, as thus defined, that the greater portion of recorded and systematic observations have been made.
A limit is imposed to the linear extension of glaciers, by the rate at which the ice melts as it descends into the warmer regions below the snow-line. In these regions the causes of decay, estimated by their whole annual effect, will predominate over those of production, and the glacier becomes thinner as it descends, till, at its lower extremity, the thickness vanishes and the glacier ceases. This dissolution of the mass takes place, in a greater or less degree, on its lower and on its lateral surfaces, as well as on the upper one, though it is at the latter surface that the greater part of the melting is produced. This process, it will be observed, is not altogether continuous during the whole year; for in the winter it will evidently be entirely arrested on the upper surface, which, at that season, becomes deeply buried in snow. The annual effect in each successive year will, nevertheless, be that due to the predominance of destructive causes. The whole mass is thus in the course of years reconverted into water, which then rushes down the valley with seeming impatience to regain the ocean from which it parted perhaps some two or three centuries before.
In contemplating a snowy mountain, we are led almost unconsciously to regard the enormous accumulation of ice and snow which gives to its summits their characteristic aspect, as being no less typical of all that is unchangeable than the rocks themselves on which it rests. We see, however, from the brief preceding explanations, that this perpetual snow, as it is termed, is rather a type of perpetual motion than of constant rest. It will be seen, in following the mutations of any constituent particle of the glacial mass, that its conversion from water into aqueous vapour, its ascent above the tops of the highest mountains, its conversion successively into snow and into glacial ice, and its final reconversion into water, and descent to the level from which it rose-that all these mutations form, in fact, one of those numerous cyclical or periodical processes by which Nature, in all her regions, unites the beauty and variety of changing aspects with a real stability capable of almost infinite duration.
It has been stated above that a glacier properly so called is the elongation below the snow-line of the general glacial mass which occupies the highest valleys and receptacles of mountains of sufficient elevation. A primary glacier will frequently originate in a single glacial receptacle above the snow-line, or it may proceed from two or more such receptacles, these partial glaciers uniting afterwards to form one principal glacier, precisely as two streams from different sources may unite to form one principal river. Thus the main glacier of the Aar, the scene of M. Agassiz's researches in the Bernese Alps, is · formed by the junction of two great tributaries or afHuents
proceeding from separate sources, and termed, from the mountains in which they respectively originate, the Finsteraar and Lauteraar glaciers, the former being on the right, the latter on the left in descending. The whole forms a rough representation of the letter Y. The length of the resulting glacier, from the point of junction of these two principal tributaries to the lower extremity of the glacier, is nearly five miles, and its greatest width, which is at the junction, is upwards of three quarters of a mile. There are also many minor tributaries to this glacier, most of which unite above the junction to form respectively the two great tributaries, while, below the junction, four distinct lateral tributaries swell the united glacier by flowing into it from the valleys, along its precipitous flanks. The glaciers from Mont Blanc at Chamouni, the scene of Principal Forbes's more detailed observations, are also among the most important of the Alpine glaciers. Other glaciers on the southern side of Mont Blanc, the glacier of Zermat descending from Monte Rosa, the glacier of the Rhone and others, will be recollected as among the principal primary glaciers which have most occupied the attention of glacialists. The same general description is applicable to them all.
The term primary is generally used, as we have used it above, to denote the glaciers of large dimensions. There are also secondary glaciers, the horizontal extent and thickness of which are much smaller than those of a primary glacier. The inclination of the beds on which they rest is usually much greater than in the larger glaciers, and they are generally restricted to higher localities on the sides of the mountains. We are not aware of any series of accurate observations having been made on these smaller glaciers. We would recommend them to the notice of future observers. It would not only be curious to observe how