versation. Taylor's Natural History of Society and other writings; Bernard's Synagogue and Church, translated and condensed from Vitringa; and Dr. West's Sermon on Reserve in Teaching Religion, (a discourse which conveys a high feeling of respect for the author,) are among the writings which had thus their origin. We have understood, also, that a very pretty story, entitled "Reverses," and "Conversations on the Life of Jesus Christ," &c. &c. are by a still nearer connexion. But we must resist all these tempting themes for the present, with the expression of our anxious hope soon again to meet Archbishop Whately in some of those walks, which he is so well qualified to enrich and adorn.

ART. IX.-Travels through the Alps of Savoy, and other parts of the Pennine Chain; with Observations on the Phenomena of Glaciers. By JAMES D. FORBES, F.R.S., Sec. R.S. Ed., F.G.S., Corresponding Member of the Institute of France, and Professor of Natural Philosophy in the University of Edinburgh. 8vo. Edinburgh. 1843.

THIS work has considerable claims upon our attention. Professor Forbes has been long known, young as he is, as one of the foremost names in science-as the worthy successor of Robison and Playfair. His varied attainments, especially in mixed physics-his power of simplifying a scientific problem, by detaching the physical portion, and examining it separately, so as to fit it for mathematical analysis; and his great experience in the observations of meteorology, magnetism, and geology, point him out as peculiarly fitted for this department of scientific discovery, and as certain to neglect none of the advantages or opportunities of travel. The subject to which he has devoted this volume, is one of great interest; the Alps-the ancient hills-offer such peculiar aspects; all the operations of nature are there on so grand a scale; her phenomena are grouped together in such bold forms, and change with such rapid vicissitude; every thing is so exaggerated and gigantic, that they form a region especially rich and instructive as a field of observation. Many of the great facts in meteorology and geology, of which only a trace can be marked in the plain country, are there brought out into full light and strong relief. These regions, too, the Professor has thoroughly explored.

"I had the advantage," he says, "of receiving my first impressions of Switzerland in early youth, and I have carefully refreshed and

strengthened them by successive visits to almost every district of the Alps, between Provence and Austria. I have crossed the principal chain of Alps twenty-seven times, generally on foot, by twenty-three different passes, and have, of course, intersected the lateral chains in very many directions.”—P. 10.

The present volume, however, is confined to an account of a residence on the Mer de Glace of Chamouni-a tour round Mont Blanc and an excursion of some weeks in the valleys near Monte Rosa, during the summer of 1842; all performed with especial reference to the theory of Glaciers, and with the endeavour, by experiment and observation, to clear up some of the preliminary difficulties of that subject.

We cannot but speak of the extremely handsome manner in which the work is illustrated. We have never seen sketches giving a more accurate, as well as picturesque, notion of the glaciers; and the topographical plans, the woodcuts, and the map which accompanies the work, are executed with admirable pre

cision.

The theory of glaciers is one which, until lately, has met with but little attention. Their striking appearance, singular position, and the dangers and difficulties with which a visit to them was environed, had long made them objects of curiosity and wonder to the Alpine traveller. Few things, in fact, arrest the attention so forcibly. The moment we enter the Alpine regions, their long white masses trailing down the sides of the mountains, seem as natural pathways from the eternal snows to the valleys beneath; and long before we approach them, the turbid and resistless torrent which gushes from their foot, tempts us to follow it to its source; on a closer view, their icy-caves, their dark-blue and unfathomable abysses, lead one on with a fascination and interest that knows no bounds. This it is which year after year crowds Chamouni and Grindelwald with their visitants; the proximity of the glaciers gives their peculiar charm to these favoured spots. But few troubled themselves about their origin and formation. The ordinary ideas on the subject, as may be learned from books of education, and other popular works, were, that the ice of glaciers was formed by the partial melting of the perpetual snows which covered the tops of the mountains, whose hollowed sides they filled; and that it was the weight of these snows which gradually pushed the icy mass into the lower parts of the valley, where the heat melted them. No rain falling in the upper regions, the supply of snow was constant, and the glacier therefore continually fed and kept up. This was thought

* Pillans' Geography under " Switzerland."

an ample and sufficient explanation of the ordinary phenomena of glaciers. It did not account for all of them, but it explained the most important.

The existence of various large insulated blocks, in different parts of the world, of rocks only found in situ at a great distance, and evidently carried away from their original position, is one of the facts of geology which has always appeared most likely, when explained, to lead to a thorough knowledge of some of the most interesting changes that have taken place on the earth's surface. Masses of rock, belonging to the higher Alps, being found scattered in the plain between the Alps and the Jura, and on the flanks of the Jura chain itself, naturally called the attention of Swiss naturalists to the subject; and M. Venetz, so well known as the engineer employed on the glacier of Gétroz, first maintained the doctrine of the former extension of glaciers to the Jura, as the transporting cause of these erratics. This opinion was subsequently taken up by M. de Charpentier, and M. Agassiz, and by the latter the agency of glaciers has been extended to account for the boulders of the North of Europe. At the same time, the Swiss geologists introduced a new theory, differing from the generally received one, as to the internal formation and motive mechanism of the glaciers themselves; points which first became of general interest, when these agents were brought in, as, to so great an extent, operating to produce the present state of things on the face of the globe. This hypothesis has been distinguished by the term "the Dilatation Theory;" it seems most probable that the difficulties which the other theory presented to the idea of the agency of glaciers in transporting erratics generally, induced these philosophers to adopt an hypothesis, (which had been indeed propounded a century before, but had excited little attention,) which accounted for the motion of glaciers by calling in the aid of one agent only, cold, and did not demand the great difference of level which motion by gravity seemed to require. We are tempted to think that the one theory was introduced to build up the other, and that the dilatation theory would not have been heard of, if it had not been found so convenient to answer the objections to viewing glaciers as transporting agents. This assumption of one theory as a fact, and the modification of another to meet the assumed fact, seems something like arguing in a circle. The motion of glaciers must be accounted for, before we can explain the transportation of erratics by their agency. The first problem required to be solved, was, and is: What is the cause of the actual observed motion of glaciers, involving, of course, the question as to their formation and internal arrangement?

Now it is important for our readers to understand the simple

conditions of the problem. The glacier is a large body of ice occupying the hollow trough formed between the sides of the Alpine range; its head or upper portion is always contiguous to, and passes into the region of perpetual snow, and it is just where the line of perpetual snow finishes that the true glacier begins; on the confines of this boundary and in its elementary state, the mass consists of consolidated and partially melted snow, which is called the névé, and between this and the true glacier, there is often interposed a precipice, over which the snow is, as it were, shot, and below it the real phenomena of glaciers appear. The glacier continues along the whole length of the ravine until it comes to the plain, where from its foot a stream of water issues, and the face of the ice above this fountain is generally very precipitous and very much broken. The ice along the length of the glacier is traversed by various clefts and cracks perpendicular to the direction of its motion, and its borders and the rocks at its sides are generally covered with a vast collection of rocks and stones forming what are called moraines. This mass is apparently continually moving, the stones of the moraines are carried on by the ice and eventually precipitated over, and lie clustering round the base; and the glacier itself every summer appears to lose its level, and undergoes great loss in its surface by melting. These are the principal phenomena of the glacier world, which are apparent to the ordinary observer; and it is to this state of things, and especially the motion of glaciers, that these theories are applied as explanations of the facts observed.

The theory of glacier motion propounded by Agassiz and Charpentier is this :-That the ice is pressed forwards by an internal swelling of its parts, occasioned by rapid alternations of freezing and thawing of the water, which, from various causes, such as rain, is introduced into the minute crevices, the capillary fissures of the glacier. This theory lays little or no stress on the action of gravity, only making use of it to ascribe the downward motion of the glacier to the tendency which motion, once excited, would have in the direction of least resistance. Its supporters tell us that they do not believe in any lubricating effect of the earth's heat upon the glacier, but assume that it is frozen to its bed; and they generally neglect the pressure either of the glacier itself upon its parts or of the superincumbent snows. This explanation at first sight, we cannot but say, seems very mysterious and obscure, and to explain motion by an a priori cause, of which there really is no evidence that it exists to any extent sufficient to produce the effect.

The gravitation theory of Saussure, when strictly expounded, is quite in accordance with the popular notion to which we have alluded. It is thus stated by our author, "that the valleys in

which glaciers lie being always inclined, their weight is sufficient to urge them down the slope, pressed on by the accumulations of the winter snows above, and having the sliding progress assisted by the fusion of the ice in contact with the ground, resulting from the natural heat of the earth."

In an article by Professor Forbes in the Edinburgh Review, to which he makes frequent reference in this work, he states, as an objection to the gravitation theory, that the force of gravity alone would not be sufficient to account for the motion of the glacier; that it could not overcome the enormous friction on its bed; some glaciers having only a surface slope of 3°. This objection, however, neglects, we conceive, the actual superincumbent weight of snow at the head of the glacier, which must contribute powerfully to its motion, independently of the weight of the glacier itselfand when we consider the effect of heat below, of the streams which lubricate the mass, and the enormous weight of stones it carries, we are at no loss to account for its motion on this hypothesis; and since we find, too, in the work of M. Agassiz, allusion to a quantity of sand and silt which is found in places over which the glacier has passed, any protuberance or holes would naturally be levelled by this filling in, which would thus assist the motion of the pure ice. The objection, that, if gravity acted, there would not be an uniform but an accelerated motion, seems more plausible; but, in fact, both these objections have been answered by the actual experiments of Mr. Hopkins, which are detailed in an appendix to this work. He placed a mass of rough ice, confined by a square frame, upon a roughly chiselled flagstone, which he then inclined at a small angle, and found that the gradual dissolution of the ice in contact with the stone produced a slow and uniform motion at the slope of a degree, or even less. This shows, at least, that there is nothing opposed to first principles in the idea of the uniform motion of a glacier being produced by gravity at a small angle of elevation. A point, however, we would suggest for future inquirers, is as to the difference in rate of descent in different glaciers; the great glacier of Aletsch has a mean inclination of 3°, and those of the Dent du Midi, which form so beautiful a spectacle from the upper part of the lake of Geneva, have a slope inclined 45°; surely, if the theory of their motion being due to gravity is true, there should be a considerable difference in the velocity of their descent.

The only insuperable objection to Saussure's theory was, that while he did not insist on the glacier being held to be a rigid mass, he yet left unexplained how it could possibly pass from a wider into a narrower strait or curve round a promontory of rock, which it is well known that these bodies of ice do. It was, therefore, unsatisfactory, without some modification or addition.