after an excellent expansion of their views on subjects of archæology, physiography, and ornithology. The following attended :-The President, Rev. M. G. Watkins; ex-Presidents, Rev. C. Burrough, Dr. T. A. Chapman, Mr. James Davies, Rev. Preb. W. H. Lambert, G. H. Piper, and H. Southall; Rev. J. D. La Touche, long time President of the Caradoc Club; Members-Judge Ingham, Revs. H. Burges Bayly, W. S. Clarke, E. R. Firmstone, C. S. Hagreen, C. Harington, E. J. Holloway, H. B. D. Marshall, H. North, F. S. Stooke Vaughan, and R. H. Warner; Messrs. Attwood-Mathews, R. Clarke, J. Cockcroft, Luther Davis, C. Fortey, C. Hardwick, Jas. W. Lloyd, G. W. Marshall and friend, J. H. Parry, W. Pilley, Scudamore Powell, William Phillips, H. Vevers, and H. A. Wadworth; Honorary Secretary H. C. Moore, and Assistant Secretary J. B. Pilley; with the following visitors-Mr. John Cordeaux, M.B.O.U.; Mr. Davis, from Malvern ; Mr. Alex. Grant, E.D., from Glasgow; Mr. Joseph Hooker, from Stokesay; Mr. Thomas La Touche, of the Indian Geological Survey; and the Rev. J. Oakeley, of Hereford.

THE GREAT ICE AGE.

THE PARALLEL ROADS OF

GLEN ROY.

By the Rev. J. D. LA TOUCHE.

MR. LA TOUCHE said: The great Ice Age or the Glacial Epoch, as it is called, is one of those phenomena which, though now fully accepted by all competent geologists, is, probably, by those who have not had an opportunity of examining the evidences on which the arguments in its favour are based, looked upon with a certain amount of incredulity. But he hoped, by the help of the model now before them, to bring forward reasons sufficient to convince any one of its reality who studies the matter impartially. All feel how hard it is to realise on a warm day like that they had just been enjoying, the fact that the face of nature, which is now decked in all the glories of summer, was, not long ago, concealed below a veil of ice and snow. Still more difficult must it be to imagine a vast covering of ice, thousands of feet thick, filling our valleys, and even covering the tops of our highest mountains in past time. Yet to those who have examined them, the scoring of the rocks in North Wales and in Scotland by the blocks of stone embedded in the under surface of glaciers, and the transport of large masses of stone to our shores from their original home in the mountains of Norway and Sweden, are, in themselves, a convincing proof of the existence of an enormous ice sheet as the only efficient cause of these phenomena. But in this model, which is an accurate reproduction on a small scale of the district round Glen Roy, no one can fail to see that the terraces which are so remarkable a feature in that locality are the shores of ancient lakes, and that the theory which assigns to their formation the existence of great ice barriers caused by the descent of glaciers from Ben Nevis and the high lands at the head of Loch Arkaig, is fully competent to explain the facts. Before, however, entering on a more particular description of the locality in question, he wished to say a few words upon the cause of the Ice Age itself, and the probable date of its occurrence. Difference of opinion, no doubt, exists on these points. Some maintain that a change in the level of the land in the Northern Hemisphere must have occurred. This view has been discussed by Sir C. Lyell in his Principles of Geology, and he appears to lean to the belief that the great accumulation of ice in the Northern Hemisphere is chiefly due to geographical conditions. At the same time he attached great weight to a hypothesis suggested by Dr. Croll, which has of late been much strengthened by the arguments adduced by Sir Robert Ball from astronomical considerations, and which is of so much interest, as affording certain data as to the probable time of the glacial epoch, that he purposed briefly now to draw attention to it. The main facts are as follows: The earth's orbit is an ellipse of which the sun occupies one focus. The form or eccentricity of this ellipse is influenced by the position from time to time of the planets of the solar system, and has been calculated for the last million years. From this calculation it appears that the ellipticity very

At intervals

slowly and irregularly changes during long periods, so that while the differences of the distance of the earth from the sun in opposite parts of its annual course was 13 millions of miles some 850,000 years ago, and again 10 millions of miles 200,000 years ago, it has in intermediate periods sunk so low as 13 millions of miles, and is at present but three millions. Now it is clear that this fact would in itself produce a considerable effect when it so happened that the winter in our Hemisphere coincided with a period of maximum distance. But two other facts must also be borne in mind. First, according to Kepler's famous second law, a line drawn from the sun to the earth sweeps over equal areas in equal times, and the consequence of this fact is that when nearest the sun the earth's motion is very much faster than when further away; and the second point is the slow and regular change in the direction of the axis known as the precession of the equinoxes. By virtue of this, in the course of 21,000 years the axis makes a complete revolution, and in half that period, viz., 10,500 years, it is exactly reversed. therefore of 21,000 years winter occurs when not only the earth is traversing that part of its orbit in which it is furthest removed from the source of light and heat, but its motion is so slow that it is subject to the refrigerating effects of its position for a much longer time. When the conditions coincide with the greatly enhanced eccentricity already spoken of, it was considered by Dr. Croll that sufficient data were afforded for the production of a glacial epoch; but since the publication of these views, certain facts as to the effect of the inclination of the earth's axis to the plane of its orbit have been pointed out by Sir R. Ball in a book lately published by him, which tend to greatly strengthen the argument in favour of the astronomical theory; and it is most remarkable that these facts appear to have escaped the notice of all previous astronomers, including such men as Sir J. Herschel. It can be shown by reference to higher mathematics that while the amount of heat imparted to the whole earth during its passage from any one point in its orbit to the opposite point, is equal to that received by it during the remainder of its annual course, the distribution of the share of heat falling to either hemisphere during the period of its summer or winter, is very unequal indeed. Had the axis been at right angles to the plane of the orbit, the heat would be equally divided between each half; but owing to the obliquity of the ecliptic, in other words, the angle of inclination of the axis, an inequality is caused in proportion to the extent of that inclination. For the particular existing angle of 23° 27′ Sir R. Ball calculates that, assuming the total amount of heat imparted to our hemisphere during the year to be 100, the proportion received during the summer would be to that in winter as 63 to 37, and according to the formula by which he arrives at this result, it would appear that had the earth's axis been parallel to the plane of its orbit, as is, indeed, probably the case with the planet Uranus, the proportion would have been 81: 18. The consequences of this discovery would evidently be most important. If during the recurrence of several periods of 10,500 years the conditions of the earth were such that during its short but hot summer the northern hemisphere were receiving 63 parts of the annual heat derived from the sun, while during the very long winter it only reached 37, and that this state of things occurred when the sun's distance was 13

millions of miles greater in midwinter than in midsummer, it is plain that the effect on the temperature of each hemisphere must be very considerable. After illustrating these remarks by reference to a diagram and by the help of a small globe, a more particular description of the district of which the model is a representation, was given. The scene of the parallel roads, or more correctly, terraces, lies to the N.E. of Fort William, and between the Caledonian Canal and Loch Laggan. At its southern extremity rises the gigantic mass of Ben Nevis, the highest mountain in Great Britain. In the exceptional situation of this mountain at the lower part of the three valleys of Glen Spean, Glen Roy, and Glen Gluoy, may be found the clue to explain the occurrence of these ancient shores which for upwards of twenty miles wind along the hill sides. In most cases the highest land is found at the head of valleys, and any glaciers which in remote ages may have been formed on it when the ice age was disappearing, would pass through them down to the sea; but, in this case, these great masses of ice, descending from the heights of Ben Nevis, and meeting another ice-stream from the highland at the head of Loch Arkaig, would inevitably form a block or dam at the lower part of those valleys and thus prevent the flow of any water that might accumulate from the melting snow in depressions of the surface at a higher level. It is most important to observe that in each case the terraces terminate in what is called a "col," which means a kind of saddle at the point where two valleys unite. The plain inference from this fact is that as the ice was gradually disappearing, lakes would be formed where no opportunity was given for the escape of the water that supplied them in consequence of the great dam of ice which blocked the passage to the west; but towards the east, where, from the lower level of the land, the thaw would be more rapid, the water in the lakes would flow over the cols and escape eastwards. There are, in all, four of these terraces. That in Glen Gluoy is of comparatively small size, and is the highest of them. The other three terraces form very striking features in the Valley of Glen Roy; the lowest, which was also the last formed, extends for about 20 miles along Glen Spean and terminates at the head of Loch Laggan in the usual col, where the stream that supplies that beautiful lake, towards the west, is separated from another which flows towards the east. At their other extremity each of the roads ends abruptly high up on the hill sides, where in fact the ice barrier formed the dam by which the waters of the lake were kept at a certain level. The breadth of the terraces varies from 60 to 6 feet, being wider where the mountain sides are less precipitous, and narrower where their steepness prevented the accumulation of débris at the edge of the lake, as it was detached from time to time from the hills above. It is also probable that in winter, when the surfaces of the lakes were frozen over, much of this débris would accumulate at the water's edge, and, subsequently sinking down gradually, help to form the roads.

The President (Rev. M. G. Watkins), in thanking Mr. La Touche for his instructive and clear demonstration, said that he had traversed the district in the

year 1877, and had observed the appearances of ice action in that locality. He could bear witness to the excellency of the model which Mr. Fortey had executed in so painstaking a manner; the whole scene of his visit was most vividly brought to his recollection, and upon the model he could trace his route. The grandeur of the mountains and the gigantic scale of the former system of lakes was most impressive, and he, as an explorer and examiner, could not hesitate to follow Mr. La Touche in his theory of the causes of the parallelism of the various roads. One glance at the celebrated Parallel Roads shews the traveller to whom Agassiz has given the key (as Ariadne gave the clue of the Labyrinth to Theseus), that they are to be ascribed to the action of glaciers slowly moving down the valley. He concluded by thanking Mr. Fortey for the opportunity given to the members of having the country represented to them so faithfully, and hoped this explanation would induce many another member of the Club to go and view for himself these mighty and wondrous revelations of the Great Ice Age, those great collecting grounds of the glaciers which dammed the glens and produced so evidently these parallel terraces.