Mr. Hill's paper in the June Number of the Magazine has incited me to recur to the great question possibility of changes in the earth's axis of rotation within itself. Mr. Hill is well known to be an accomplished geologist; but he writes as if he were simply a physicist, without sympathies for the difficulties of his brethren of the hammer. Yet we feel certain that such is not the case. We know that he has studied in the field the tremendous movements which the strata have undergone, being often compressed into a small part of their original length: that he has appreciated the almost ubiquitous presence, either in past or present time, of volcanic activity: that he must feel how unsatisfactory all explanations short of a change in latitude are to account for the flora of a warm climate within the arctic circle. We therefore appeal to him, and to others similarly qualified, to look at this subject from both sides.

The following carefully and elaborately prepared list of the fossil Brachiopoda of the Lower Boulonnais has been forwarded to the Editor for publication by his esteemed friend and frequent contributor Thomas Davidson, Esq., F.R.S., who writes as follows:— “At my request M. E. Rigaux (51, Grande Rue, Boulogne-sur-mer, France) has been engaged for more than two years in drawing up complete summary of all the Brachiopoda that are to be found in the various formations composing the Lower Boulonnais.

The most important geological problem, and the one of all others which at present excites the greatest attention, is the cause of those extraordinary changes of climate which have taken place during past ages. How are we to account for the cold and Arctic condition of things which prevailed in temperate regions during what is called the Glacial Epoch, or for the warm and temperate climate enjoyed by the Arctic regions, probably up to the Pole, during part of the Miocene and other periods? Theories of the cause of those changes, of the most diverse and opposite character, have been keenly advocated, and one important result of the discussions which have recently taken place is the narrowing of the field of inquiry and the bringing of the question within proper limits.

It will probably be conceded, by those who have studied the Somersetshire portion of the British Coal-field, that the correlation of the various parts of it is not, at the present time, so perfect that any attempts to improve it are entirely uncalled for. The following conjectures as to whether some of the facts relied on as proving the commonly-accepted theory of the structure of the Somersetshire Coal-measures, and their general correlation with those in Gloucestershire, may not possibly admit of an interpretation differing from that usually assigned to them; are put forward in the hopes of indicating a line of research which may eventually, when modified by the results of further investigations, lead to a solution of some of the numerous difficulties at present standing in the way of a satisfactory understanding of this extremely complicated district.

In his important paper on the Physical Structure of West Somerset and North Devon (Quart. Journ. Geol. Soc., vol. xxiii. p. 568), Mr. Etheridge incidentally refers to a felstone at Bittadon, saying of it (p. 609): “There is no proof that the igneous rock at Bittadon is eruptive.” At the time when these words were written, it was undoubtedly impossible, from the nature of the exposure, to decide whether the rock was intrusive or interbedded; but, on visiting the locality in September, 1876, I found that a small quarry (for road metal) had been opened in the felstone, and its relations to the sedimentary rocks were pretty clearly exposed.

The land-plants lately discovered both in the American and Continental Silurians seem to be attracting attention, while those found in Ireland nearly a quarter of a century ago appear to be quite forgotten. This is probably due to the unsatisfactory condition in which the classification of the Irish Silurians are left at the present time; perhaps therefore it is allowable for me to give a short description of these rocks.

From the sandstone (i), which Professor Ansted asserts, though without giving his reasons, to be “no doubt modern,” and to have been “deposited before” [just before?] “or during the last great elevation,” down to the superficial clays and sands, there is not a scrap of any other Secondary or Tertiary rock in situ to be found on any of these islands. We leap at once from this sandstone to clays and sands of Post-Tertiary date. Mr. Duncan, in his History of Guernsey (edit. 1841, p. 513), says that “flint and chert nodules, containing impressions of shells, etc., are frequently discovered beneath the soil in places which preclude the probable transport by the hand of man.”

After much slipping and sliding—for the small stream of water which flows down the pass had often glazed it from side to side—we reached the village of Yamborshan, just outside the Kalgan walls. Here I was well received by the Russian Postmaster, M. Shismaroff. This village, like Kalgan itself, is romantically situated in a defile, which is bounded by mountainous cliffs of a volcanic rock, called by Pumpelly a porphyritic trachyte. Before entering Kalgan, you pass underneath a gateway in the famous Great Wall of China. Right and left from this point, it rapidly ascends to the summit of the cliffs, which bound the defile, and its towers are seen standing on pinnacles of rocks, and looking over precipices from positions which seem inaccessible.

Having paid but little attention to geological literature during the last two years, it was not until September, 1878, that I became aware of Mr. A. J. Jukes Browne's article in the GeologicalMagazine of August, 1877. In this article, amongst other matters, the author criticises very fairly the classification of the Upper Greensand and “Chloritic Marl,” so-called, as set forth in my paper on the Cretaceous Rocks of Beer Head. In justice to certain questions involved, I find myself compelled to reply to this criticism, and to say a few words besides respecting the Chloritic Marl and Upper Greensand.

About 5–30 p.m. on Thursday, 13th November, I said good-bye to Lake Baikal, and branched off upon a road to the right leading to Cabansk. Along this road, which was a very bad one, there was an apparently untouched forest of birch and pine, with here and there a clump of aspen. For some distance upon my left extended a wide lake, which joined the Baikal. After much reckless driving across wide trackless plains, through gaps in ridges, snow drifts and clumps of trees, with a wild and drunken coachman, at half-past eight I found myself at the post station of Cabansk. After a windy and bitterly cold night, I was next morning at the station of Palavinsaya, the country round which is hilly and pretty. The next station was situated in a plain between sloping hills and isolated peaks. These hills being without wood, the country had an open appearance. As I went on, the snow, which I had been told in Irkutsk would be continuous as far as Kiachta, grew less and less, and at the station where I next changed horses, I had to abandon the sledge I had purchased and hire a carriage. Although the roads were now tolerably free from snow, the surrounding hills were still white with it. The next morning I passed the station of Povorotnaya. The soil now became sandy, and the only trees were pines. The way in which these were dotted about in clumps gave a park-like aspect to the district.

Near Kildale, a small village on the North Yorkshire and Cleveland Railway, not far from the source of the river Leven, a railway cutting close to the station shows, in descending order, the following section.

The late Dr. Falconer figured in the “Fauna Antiqua Sivalensis,” a fine lower jaw of an adult Elephas primigenius, preserved in the National Collection, and of which he gives two views, the first as seen from above, the second a side view; and in the descriptions of the plates in the above work given in his “Palæontological Memoirs,” vol. i. p. 439, occurs the following note regarding it: “Plate xiii. A. fig. 3.—E. primigenius. English fossil specimen, with two last true molars on either side. In the last left molar there are eighteen plates in 7·7 inches. The jaw has a short beak, and one inner mentary foramen on either side. In this, as in figs. 1 and 2, representing the jaw at different ages, it is to be noted that the opposite lines of molars are more or less convergent instead of being parallel, or nearly so, as laid down by Cuvier.

By way of introduction to the subject of this paper, I will very briefly describe the physical features of the country drained by the River Calder. We shall thereby gain a clear idea of the present configuration of the Calder valley and better understand how the forces have operated which have produced the grand diversity of hill and valley, of moorlands bleak and wild, of precipitous crag, and steep, wooded slopes, and of the lower lands, rich and fertile, which extend along their base. To know clearly what has been done, is more than half to understand how it has been done.

A considerable part of the material forming the present communication was collected as long ago as 1862, but the specimens obtained at that time, with the notes thereon, remained in abeyance until quite recently. On a renewed examination of them, it appeared that much of what had been noted down had not been superseded, and this induced me to go through the whole of it again, and make such additions and modifications as seemed necessary to bring it into its present form. And I have done this in the hope, and indeed in the belief, that it will serve a twofold purpose. It will make known some forms which are new, not only to the particular locality, but also to the catalogue of English species; and it will furnish a more complete list than has yet appeared of the species from one of the best-known Coral-reefs of the Inferior Oolite.

As I am one of those who find difficulty in understanding the preservation of stratified deposits beneath the Till, I would like to point out to Mr. J. Geikie that he has not correctly stated the difficulty in his paper (Geol. Mag. Feb. 1878) on “The Preservation of Deposits under Till or Boulder-clay.” The difficulty really lies in the explanation of how the Till itself was deposited: were that clear, the preservation of beds beneath it might be at once intelligible. Admitting the passage of an ice-sheet across the country, admitting further that the Till is the moraine profonde of such an ice-sheet, the accumulation of 100 feet of Till beneath the ice-sheet is a phenomenon which has not been explained, and cannot be passed over as unimportant. A moving mass of ice, 2000 feet thick, seems a formidable agent of erosion; yet where I now write nearly 100 feet of Till intervene between the surface and the Carboniferous rocks, which, where exposed, shows striations having the usual compass bearing for this neighbourhood. The greater portion of the Till hereabouts is derived from the Carboniferous rocks of the district, but numerous boulders of granite, felstone, schist, and of Old Red Sandstone sedimentary and volcanic rocks, show that the ice had brought materials from a wider area. The limits of the Carboniferous series are about twelve miles to the west and northwest of Glasgow, that being the direction whence the ice came. As the ice of a modern glacier pushes the results of erosion before it, we may conclude that the old ice-sheet with a pressure of about 1000 lbs. to the square inch did the same; indeed, Mr. Geikie has already accepted this “idea as to how an ice-sheet would behave,” but without explaining how the alternate exposure and concealment was effected in the presence of very thick Till. It may be said that the ice pushed its moraine profimde before it, but then Hugh Miller's “pavements” have always been referred to as proofs that the ice overrode not displaced the Till already accumulated.

The possibility of change in the position of the Earth's axis seems periodically to attract attention. This is happening now. Professor Haughton has written upon this subject, Sir William Thomson has alluded to it, while two important papers have been read upon it, one by Professor Twisden before the Geological Society, the other by Mr. George H. Darwin before the Royal Society. This article is an endeavour to exhibit to the general reader the assumptions with which they have started, and the results they have obtained.

I am grateful to Mr. Hill for noticing my former paper “On Possible Changes of Latitude on the Earth's Surface” in his letter, October, 1878, p. 479. I wish, however, that he had gone into the subject more in detail; in which case I, and perhaps others, would have felt more satisfied with his reply. He epitomizes my appeal to physicists by making me ask, “Assuming that a thin crust surrounds a fluid substratum, could then a deformation shift the crust over the nucleus?” And he replies that, Mr. G. Darwin having proved that the earth is “enormously stiff,” the discussion would be fruitless. But in this statement of my question and reply to it, he has omitted what seems to me the important proviso, based on Hopkins’ reasoning about the mode of cooling, that this fluid substratum is shallow, and encloses a rigid nucleus; and given no reply to my inquiry whether such a supposition might not afford the required rigidity.

It seems to be one of the chief objects of the British Association for the Advancement of Science in changing the place of meeting every year, to bring more prominently before the members of its respective sections such points of interest in their own department of Science as are afforded by the various localities. In accordance with this principle, I beg to lay before you some observations concerning the geology of a district not more distant than about two hours' railway journey from Dublin, which will, I trust, be of peculiar interest on the present occasion. The district I refer to is the hill country north of Dundalk, of which Slieve Gullion forms the most prominent feature. This mountain is a somewhat isolated mass, attaining an elevation of about 1900 feet, and is situated to the north-west of the hilly and picturesque country lying between the bays of Dundalk and Carlingford, or due west of the more remarkable group of the Mourne Mountains.

For many purposes it is often desirable to form some approximate estimate of the area occupied by a particular deposit, and in working out the topography of any county or district (especially for agricultural purposes), it is frequently necessary to ascertain the relative extent covered by the various formations. This information, in every instance which has come under my knowledge, has been obtained by measuring on the map with a rule, and entering the results, according to the scale, as so many square miles of surface. Nothing being more uncommon in nature than a straight line of boundary, every one who has made the attempt must be aware how impossible it is to reduce with any degree of accuracy to a geometric figure such lines as those to be found on most geological maps, and having recently had occasion to make a calculation of this nature, for Devonshire, I wish to describe a very simple method which I adopted with success.

Those who maintain that Till or Boulder-clay has not only originated but accumulated underneath glacier-ice may sometimes have felt puzzled to account for the preservation of beds of more or less incoherent materials below a deposit which they have so many cogent reasons for believing to be a true moraine profonde.