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this by his high reputation and wide acquaintance among men of science, and the esteem in which he was held by them, as well as by his zealous activity as an observer, although his physical theories were never received with much favour. His second work, the 'Systeme Glaciaire,' remains the most copious deposit of accurate and careful observations which we possess on many glacial phenomena, as his map of the Aar is by far the finest topographical record we have of any glacier and its superficial phenomena. Principal Forbes's 'Travels in the Alps' is also a work full of interesting matter relating to Alpine glaciers generally, and his sojourn among them. His researches were unwearied, and he acquired and communicated to us a large amount of general and detailed knowledge of glacial phenomena. For this, and for the general interest with which he helped to invest the subject, we consider the scientific world to be greatly indebted to him. The prevailing defect of his observations is that they are subordinated too much to two dominating ideas, the viscosity of glacial ice and his supposed origin of the veined structure; and therefore it is that his observations, though extending generally over a wider range than those of M. Agassiz, are less valuable in many cases where greater detail and minuteness are essential. We think that for many years imperfect justice only has been meted out to the 'Systeme Glaciaire' in this country, and that our estimate of the claims of its author, as well as those of some few other foreigners, may have been perhaps, if we may use the expression, somewhat too insular. There is scarcely any part of Principal Forbes's speculative theories to which we can assent, and it is quite certain that much of his mechanical reasoning is altogether erroneous. Mr. Hopkins was the first to explain the sliding of glaciers and their unaccelerated motion. He has also applied accurate methods of investigation to the solution of many of the mechanical problems which glacial theory involves. Dr. Tyndall in recognising the necessity for precise definitions, and for exact modes of research both in the mechanical and experimental branches of the subject,, has afforded excellent aid to the advance of glacial theory. He has done good service also in the observations he has made; but it is in the substitution of a determinate and beautiful experimental result for a hypothesis unfounded on any determinate property of matter that he has rendered the greatest service in this department of science. The results of regelation explain exactly what glacial theory required to be explained; but they do not effect this through the medium of viscosity. Regelation does not use viscosity, but supersedes it, and renders not merely the word itself, but any definite idea which has ever been attached to it, useless in all, exact reasoning on the subject. We cannot refrain from appealing in the name of exact science, and on behalf of the rightful claims of exact philosophers, against the merging of the definite into the indefinite, or the Sliding and Ret/elation Theory into the Viscous or Plastic Theory.

In what we have said on regelation we have been anxious to point out that the value of the actual results of regelation is little diminished for the glacialist by our ignorance of the exact modus operandi by which those results are produced. The theory of gravitation might be advanced if some astute philosopher could prove that gravity was only the effect of some still simpler property of matter; but Physical Astronomy, in the sense in which that term is used at present, could scarcely be thereby rendered more complete than it is; and so, though the process of regelation may hereafter be explained, the discovery of the results of that process will not the less constitute a decided and independent step in glacial science, and one which, we believe, will always hereafter be recognised as such.

We have already mentioned the name of M. de Charpentier, but we should not do justice to him if we did not recognise his claim as having been one of the first glacialists, though preceded several years by M. Venetz, to direct attention to the former great extension of the Alpine glaciers, as manifested by the enormous masses of blocks and debris, which have evidently been derived from distant localities, and the transport of which he attributed to the agency of glaciers. But this is a subject which our space will not allow us to discuss; and, in fact, it may rather, perhaps, be regarded as belonging to the wide domain of Geology than to the more restricted one of Glacial Theory. In the later history of our planet it has opened to us a new and interesting page which has yet been but imperfectly deciphered, and which can only be truly interpreted by the combined efforts of the geologist and "the glacialist We confess that we are not without apprehension that many geologists may be disposed to accept theories in which the action of glaciers is the leading agency, without due regard to those mechanical and physical principles to which the motion of glaciers must in all cases be subordinated. We shall take one important point to elucidate our meaning. We have seen (p. 79) that below the snow-line the thickness of a glacier decreases from year to year, principally by the melting away of its superficial portion. Suppose the thickness of a glacier at any assigned point of its course to be 1000 feet, and to diminish 10 feet annually. Let us further suppose the glacier to move at the rate of 400 feet a year. Then for every 400 feet in the length of the glacier, measuring towards its

lower lower extremity, there will be a decrease of 10 feet in the thickness, which will consequently be reduced to zero at the distance of 40,000 feet, or about 7-J miles, which would be the length of the glacier below the point at which its thickness has been supposed to be 1000 feet. The wasting of 10 feet annually in thickness is very nearly the estimate of M. Agassiz, founded on careful experiments, made on the glacier of the Aar, near the junction of its two great tributaries, and at the height of some 8000 feet above the sea. The motion of 400 feet in a year is greater than the mean annual motion of the Aar glacier, and less than that of the Mer de Glace. It may be taken as a sufficiently near approximation to the mean motion of the Alpine glaciers.

Let us take an actual example, analogous to the imaginary one above given. Erratic blocks exist on the flanks of the Jura opposite the mouth of the valley of the Rhone, at the height of at least 3000 feet above the Lake of Geneva, and it is universally allowed that they must have been transported by some means or other from different localities in the valley of the Rhone. The favourite theory at present appears to be that their transport was effected by a glacier which descended the whole length of the valley just mentioned, and thrust itself across the central Swiss valley, to deposit its burden of blocks on the sides of the Jura in the form of a terminal moraine. We have here no intention of discussing the truth of this theory ; we wish simply to point out some difficulties which, it would appear, have not engaged the attention of those who advocate it. According to Charpentier, the highest lines of erratic blocks may be distinctly traced along the sides of the Rhone valley, their elevation on either side of it at Martigny being about 2500 feet, and at the mouth of the valley 2300 feet above the river. We take these heights as indicative of the depth of the ancient glacier between the two places just mentioned. Now let us conceive the conditions as to the motion of the glacier and the rate of its wasting away to be the same as in the imaginary case above taken, or very nearly the same as in the Aar glacier at the present time; and let us also suppose, to make the analogy complete, that the valley of the ancient glacier was continued beyond its present termination. It then follows, from a calculation like the above, that it must have extended some 15 miles beyond the mouth of the present valley. But this ancient glacier, instead of continuing along a troughshaped valley, must have debouched into the open plain of Switzerland, and thus have been at liberty to diverge in nearly all directions within a semi-circle, like the glacier of the Rhone from the foot of its fall. Consequently, the external surface

exposed exposed to the dissolving influences of the sun's rays, and of the atmosphere, would be much increased, and the thickness of the glacier would be reduced to zero long before its remoter boundary had attained a distance of much less than 15 miles. And here it will be observed, that the temperature of the Swiss valley is tacitly supposed to be reduced to that of the middle region of the Aar glacier, at an altitude above the sea of about 8000 feet. Nor would that, as our calculation tells us, be cold enough to secure the protrusion of the glacier, as above supposed, to the flanks of the Jura, a distance of 50 or 60 miles. In fact, it would be necessary that the temperature at the level of the Lake of Geneva should be lower than that of the snow-line, t. c, lower than the present mean temperature in the Alps at the height of about 10,000 feet It would be useless to talk of this enormous depression of temperature being produced by any peculiar disposition of land and sea. The only conceivable terrestrial cause to which it could be chiefly referred, must be the natural elevation of the whole region to the amount just stated. Then the glacial mass in the Swiss valley would not melt away, as it would below the snow-line, in its transit to the Jura, which it would reach provided the fall between the mouth of the Rhone valley and the top of the Jura chain were sufficient to secure its motion in that direction. This fall would require the Alps to be raised some 4000 or 5000 feet more than the hills of the Jura. Mont Blanc would thus become nearly 30,000 feet high, while all the lower regions surrounding it would be raised to an elevation of 10,000 or 12,000 feet above the level of the sea—consequences which might well alarm the boldest catastrophist, and dispose us to search carefully, before we finally admit them, for some simpler mode of transporting erratic blocks from the Alps to the Jura.

The great difficulty which besets all theories involving an extreme extension of ancient glaciers in Western Europe, arises from the apparent impossibility of assigning any adequate terrestrial cause, except that of extreme elevation, for the enormous depression of temperature in these temperate latitudes, which such theories tacitly demand. Terrestrial causes for considerable variations of climatal temperature have been assigned, depending on the influences of warmer or colder ocean currents, and of possible changes in the disposition of sea and land; but it would be futile to attribute to such causes the immense depression of temperature required in a case like that discussed above. But our immediate object is not to discuss the various causes by which terrestrial temperature may be affected, but to remind geologists of the physical impossibility so clearly indicated by established glacial

facts facts and theories, of any prolongation of glaciers beneath the snow-line, beyond those limits which may be consistent with the extent of such prolongation calculated as in the preceding example. At present we have only to recommend that in framing the theories which erratic blocks may suggest to us, we should endeavour to bring them into strict accordance with the mechanical and physical principles which govern the motions of existing glaciers, as well as with all associated geological phenomena, and thus to establish that harmony of which we have spoken in the commencement of this review, as the final and most perfect test of scientific truth.

Art. IV.—1. The Empire. A series of Letters publislied in 'Tlie Daily News' in 1862 and 1863. By Goldwin Smith. Oxford and London. 1863.

2. Lectures on Colonization and Colonies, delivered before the University of Oxford in 1839, 1840, and 1841. By Herman Merivale, A.M., Professor of Political Economy. New Edition. London. 1861.

3. Reports of the Past and Present State of Her Majesty's Colonial Possessions, transmitted with the Blue-books for the Year 1860.

4. Twenty-first General Report of the Emigration Commissioners.

5. Letter to the Right Hon. Benjamin Disraeli, M.P., on the

Sesent Relations of England with the Colonies. By the Right on. C. B. Adderley, M.P. New Edition. London. 1862.

THAT it should even be made a matter of question by any, whether Great Britain shall retain her colonial possessions, is something new and strange. But since there are men among us, and men of accomplishment and ability, who take the negative side* and who would resent the imputation that their words are no more than the casual effusion of a passing and thoughtless grumble, we must require them and others to bestow somewhat ampler reflection upon the subject

The arguments of those who, like Mr. Goldwin Smith, inculcate the necessity of dismembering the colonial empire are obvious and simple, and based on the narrowest possible view of a few facts, excluding from consideration many facts of far greater importance. These arguments are generally stated as follows: Colonies 'do not pay.' They are useless for the purposes of commerce, and too costly for the purposes of power. Since the recognition of the principles of Free-trade by the leading statesmen of the great parties, they are superfluous for

the

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