Owing to its greater specific lightness, cream ascends to the top of the vessel, but it can be easily made to diffuse itself through the milk by slightly shaking it before uncorking the bottle. As the vessel is not quite full, a small quantity of butter may have been formed, and the milk may have become somewhat less rich, but it will still be pure and natural milk, without any strange taste. Thanks to the progress of science, of which I am happy to be the representative, France can yield with profit to England her fruits, her vegetables, her eggs, and now offers her prepared milk for the wants of the army and navy, having nothing to fear from the longest voyages, nor from the excesses of heat and cold.

On a Symmetrical Arrangement of Oxides and Salts on a Common Type. By Dr LYON PLAYFAIR.-Salts, according to the present views, may be constituted of an oxide and an acid; of an electro-positive element and an electro-negative salt radical; or on the type of water, in which the hydrogen is sometimes replaced by an electro-positive element, sometimes by an electro-negative compound. The author adopted the whole series of metallic oxides as typical of salts, supposing that two equivalents of the metal were present in all the oxides except the magnetic oxide. He contended that neutral salts are not formed on the type of a basic oxide, such as water, but on that of a neutral oxide, such as peroxide of manganese or peroxide of hydrogen, of the general formula, 02(MM)02. Two equivalents of the oxygen in this type may be replaced in a neutral salt by an anhydrous acid, so that the general formula of a neutral salt is either O(MM)A2, or half that value, in which A represents any acid. The author showed that many facts supported the idea that an anhydrous acid could substitute oxygen directly, and vice versâ. Thus, carbonate of manganese heated in air becomes peroxide, oxygen substituting the acid; while peroxide of copper loses oxygen in air, and becomes a carbonate. Barytes heated in air absorbs oxygen, and becomes a peroxide; heated with sulphuric acid, it becomes a sulphate: both oxide and salt being formed on the same type. The author then proceeded to show that as there are varieties of oxides, so also there are varieties of salts, each constituted on an oxide type. Salts of suboxides represent the protoxides; subsalts, with two equivalents of an oxide and one of an acid, are formed on the type of sesquioxides; while those with three of a base and one of an acid, like phosphate of soda, are formed on the type of magnetic oxide of iron. The sesqui-salts, on this view, are on the type of manganic acid, O,(MM)A, being like O(MM)O3. The author then proceeded to show how various relations became apparent, if the oxygen in the oxides were arranged in the simplest form of an axis and equator around the metallic nucleus, according to a conventional system on a plane surface. The existence or deficiency of symmetry in the structure of a body becomes thus indicated. As a general conclusion, when there is an equal balance in the molecules of oxygen, or of electro-negative bodies playing its part, then rest or neutrality results; when the structure wants balance or symmetry, then activity is manifested-basicity when the electro-positive molecules predominate; acidity when the electro-negative are in excess. By writing minus points to show the want of symmetry, it is possible to indicate à priori whether an acid is monobasic, bibasic, or tribasic. In conclusion, the author referred to the oxides of nitrogen, chlorine, and carbon as illustrations of the importance of symmetry. Writing them all on four-volume formulæ, it is necessary to double them when the compound has an uneven number of molecules of oxygen; but the oxides of an even number do not require this duplication. Further, it was shown that the symmetrical oxides are neutral or only feebly acid in character in the case of the oxides of electro-negative elements. Thus hypochlorous, chlorous, and chloric acids are uneven, like

nitrous and nitric acids; while binoxide of nitrogen and the peroxides of chlorine and nitrogen are neutral, from there being a balance in the molecules of oxygen. In like manner, oxalic acid, with an uneven number of atoms of oxygen, is more powerfully acid than carbonic acid, where the conditions for symmetry are more nearly satisfied.

To exhibit a Photograph of Fluorescent Substances. By Dr GLADSTONE. It is well known, on the one hand, that the chemical action of light resides mainly in the most refrangible rays, and on the other hand, that these rays are altered in their refrangibility and effect on the visual organs by fluorescent substances. It occurred to the author that such substances would probably exert little photographic action. Hence he had made two drawings on sheets of white paper, one in an acid salt of quinine, the other in a very pale solution of chlorophyll, and had taken photographs of them. Although the drawing in quinine was quite undistinguishable from the white paper, and the chlorophyll drawing nearly so, when they were viewed in the same camera for adjusting the focus they were strongly marked on the photographic image by the little chemical action that had been exerted by them. The sheets of paper, and the drawings developed on the glass plate, were exhibited, showing that what theory had suggested as probable, was true in fact.

On a New Mode of Bread-making. By Dr ODLING.-By this process the carbonic acid is produced independently of, and superadded to, the flour, which consequently undergoes no modification whatever. The carbonic acid gas is stored in an ordinary gas-holder, and is pumped therefrom into a cylindrical vessel of water, whereby the water becomes charged with gas. This soda-water is mixed under pressure with the flour, and the resulting dough becomes vesicular on removing the pressure. It is. then divided into loaves and baked. This process is so rapid that in an hour and a half from the first wetting of the flour, a sack of flour is made into two-pound loaves. The advantages of this new mode are-its cleanliness; from the beginning to the end of the operation, neither the flour nor the water is touched by the human feet; it conduces to the health of the work-people; it is a very rapid process; it is certain and uniform; and it prevents any deterioration of the flour, so that by this process you can use flour which would require alum in the ordinary process.

Report on Field Experiments on the Essential Manuring Constituents of Cultivated Crops. By Professor VOELCKER.-The field experiments, which extended over a period of four years, had special reference to the tur nip-crops. Dr Voelcker described the plan upon which these experiments were undertaken, and mentioned the results which were obtained. Amongst other points of interest to the agriculturist, it may be noticed, as the result of four years' experience in the growth of turnips under particular conditions.-1. That fertilisers destitute of phosphoric acid do not increase the yield of this crop; 2. That phosphate of lime applied to the soil in the shape of soluble phosphate (super phosphate) increases this crop in an especial manner, and that the practical value of artificial manures for root crops chiefly depends on the relative amount of available phosphates which they contain. Thus it was shown that 3 cwt. of superphosphate per acre produced as large an increase of turnips as 15 tons of farm-yard manure; 3. That ammoniacal salts and nitrogenised constituents yielding ammonia on decomposition, have no beneficial effect upon turnips, but rather the reverse; 4. That ammoniacal salts applied alone do not promote, as maintained erroneously, the luxuriant development of leaves; but that they produce this effect to a certain extent when salts of ammonia are applied to the land in conjunction with the mineral constituents found in the ashes of turnips. The Report likewise states that numerous analyses of turnips have been made, from which it appears that

the more nutritious and least ripened roots invariably contain less nitrogen than half-ripened roots, or turnips of low feeding qualities. In the latter, the proportion of nitrogen was found, in several instances, two to two-and-a-half times as high as in roots distinguished for their good feeding qualities. Similar experiments upon wheat showed that nitrogenised ammoniacal matters, which proved inefficacious in relation to turnips, increase the yield of corn and straw very materially, and that the increase of wheat was largest when the ammoniacal constituents were associated with mineral matters.

GEOLOGY.

On the Geological Structure of the Vicinity of Aberdeen, and the north-east of Scotland. By JAMES NICOL, Professor of Natural History, Aberdeen. The author said-It has been thought that a short sketch of the geology of this locality might interest our visitors from the south. To illustrate this generally, I have had a large copy of that portion of my Geological Map of Scotland prepared. This, of course, does not give minute details, but still I have no hesitation in saying that it is more accurate than any other, as I have not only corrected it in many points myself, but have had the use of much material collected by my friend Mr A. Cruickshank.

Though scarcely needed, it may be mentioned that Scotland consists of three natural geological divisions :

1st. Southern region of Lower Silurian Rocks of Murchison or Cambrian of Sedgwick. This region consists of greywacke and clay slate, rising into lofty broad-backed mountains, separated by wide valleysthe dales of the old Borderers.

2d. Central region of Old Red, Coal, and Trap. This contains only about one-sixth of the surface (5000 square miles), but full two-thirds of the population of Scotland, and a far larger proportion of the mineral wealth and manufactures of the kingdom.

3d. Northern Region of Primary or Crystalline Strata, broken through by Granite, and set in a framework of newer formations. It contains two-thirds of the surface, but little more than one-fourth of the popula tion. It is in this region we are now met, and to one portion of it that I mean specially to direct your attention.

The kernel of this whole region is the GRANITE. This forms some of the highest mountains, and some of the lowest land in the district; of the former I may mention Ben Macdhui (only rivalled in Britain by Ben Nevis) and the Cairngorum mountains on the north of the Dee; and on the south of that river Loch-na-gar, Mount Keen, Mount Battock, and other giants of the Southern Grampians. These, the principal mountains, are usually round, massive, dome-like, with a deep corry on one side, as if formed by the falling in of one-third of the mountain, and thus bounded by lofty, rudely prismatic precipices, rising from a dark, black tarn in the centre of the hollow. In consequence of decomposition, the granite mountains are usually covered with huge feather-bed-like rocks, piled up in cairns of rude masonry, and the shelter of the red deer and ptarmigan. The rock in these mountains is rather fine ground, uniform in structure, and often reddish coloured. It contains cavities in which the rock crystal or Cairngorum stone, the topaz, and the beryl are found. Bennachie, one of the outposts of these mountains on the north-east, though not high and easily accessible, is very interesting. It looks out on the south-west to the loftier ranges of the Grampians, with patches of snow even at the end of summer, and on the north-east over the plains of Buchan-low,

undulating, and treeless, but rapidly changing, under the industry of the inhabitants, from bleak moors to fertile corn-fields.

A large portion of these north-eastern plains too consists of granite; in them, however, occupying the lowest, not the highest position, as in the mountains. This fact shows that the granite is the basis on which the strata rest, and hence is exposed where they have been cut away by denudation. A fine section of the granite is seen in the sea-cliffs south from Peterhead, where it is intersected by long, narrow gullies and deep caves, in which the restless surge of the North Sea keeps up an incessant tumult. Hence some of the more remarkable of these excavations have got the name of the Bullers of Buchan.

The rock, in this region, is red or gray, according to the colour of the felspar. It often contains hornblende, or is a syenite, as in the tract to the north of Huntly, and in other places again becomes almost a fine grained greenstone or diorite. This diversity of mineral character proves that the granite is not all of one period of formation. The veins of granite, in the granite itself, show this even more clearly. These are beautifully seen in Rubislaw quarry, close to the town, where there is one very remarkable vein of coarse granite, composed of very large twin crystals of orthoclase felspar and mica, in a basis of quartz, along with long broken prisms of schorl, Davidsonite, or impure beryl and garnets. The quartz in this vein is also remarkable for numerous cavities enclosing fluids, which Sorby uses as natural thermometers to tell the temperature or pressure under which the rock was formed. The latter, he says, was for the fine granite or main body of the rock 78,000 feet, for the coarse granite or veins 42,000 feet.

Of the stratified rocks the first, GNEISS, Covers a wide extent in Aberdeenshire, and generally in close proximity to, or resting on, the granite. It is thus seen in the valley of the Dee above Braemar, reposing on the granite in thin even beds, at a low angle, and apparently undisturbed by the inferior igneous rock. In many parts of the low country the same relation occurs, the gneiss often forming the hills, the granite the intervening valleys. But in other cases, as in the hills north of Ballater, the two formations are seen side by side. The gneiss, in many localities, is full of granite veins; but whether these belong to the great mass of granite, or are of a different age, is not easily determined; and the question seems never to have been fully or fairly worked out. Such veins are well seen on the coast to the south of the city, especially near Girdleness and the Cove, and also in many parts of the mountain chain on the south side of the Dee. Veins of felspar, porphyry, and of trap, are known in the gneiss on the same coast, and in many other localities.

The gneiss is usually the common variety of quartz, felspar, and mica. But varieties with hornblende, passing into hornblende slate, are also common. The latter are well seen in the hills along Glen Muic, and up to the top of Morven. The beds of gneiss are seldom flat or even, more often highly contorted.

In the Braemar district the gneiss is covered by beds of limestone and quartzite the latter, perhaps, only a variety of the gneiss. It often contains much magnetite, apparently replacing the mica. Indeed, iron, both as the oxides and pyrites, is very common in all these rocks; strongly impregnating many of the springs, and finding its way into the sands of the rivers and of the sea-shore. From the Cairngorum mountains great ridges of quartzite run north into Banffshire, and to the coast near Cullen. In some places in this region it appears to lie below the mica slate, but their exact relation is obscure. In other parts of the low country, as in Mormond Hill, the quartzite rests on the gneiss.

Mica-slate in Scotland is most common in the south-west Grampians; but

in this district it becomes greatly attenuated to a very narrow zone. In the Glensheeard Stonehaven sections, the mica-slate appears to lie below the gneiss, and not over it, as usually represented. There are great tracts of mica-slate also in the north-west, between the Spey and Deveron, where it is intermixed with gneiss and clay-slate, but the relations of the deposits are little understood. It often contains garnets, more rarely andalusite, and some other minerals.

Clay slate also covers a considerable share in this district, chiefly to the south of Banff and the Troup Head. It is quarried in several places for roofing-slates, as near the Troup Head, in the Foudland Hills, and near Gartly. These slates are wrought on lines of cleavage, the bedding being in general scarcely perceptible. It has been said that fossilsgraptolites-occur in this rock; but there is no foundation for this statement. I formerly described these clay-slates as probably Silurian; but this is only a theory, and as the clay-slate in the southern Grampians appears to dip north below the mica-slate, this view now requires confirmation. In Glenshee a curious series of black carbonaceous slates, containing graphite, like those of Easdale, occur. Graphite is also found in other parts of this region, in the metamorphic strata-a most important fact in reference to the theory of these rocks.

The Old Red Sandstone chiefly occurs on the outskirts of the region we are considering. The principal mass within it runs south from Gamrie-a locality well known for its nodules with fossil fish. Another isolated, but interesting portion, occurs round the ancient Castle of Kildrummy, in which impressions of plants have been found. A curious mass of conglomerate at the Old Bridge of Don, probably belongs to the same deposit. On the southern limit of the moss, the Great Red Sandstone formation of Strathmore begins, and is well seen in huge beds of red sandstone and conglomerate near Dunnottar. The conglomerate must be regarded as marking rather the shore-lines or certain peculiar local conditions, than any particular zone in the formation.

At the other extremity of the moss, on the Spey, the Morayshire deposits begin, with numerous fishes at Pynet Burn, Dipple, &c. Still further west are the beds with reptilian remains at Elgin, probably in the upper Old Red, or some newer formation, but beyond the limits of this paper.

Higher deposits are only known in fragments. Such is the portion of lias near Turriff, perhaps in situ; but other masses of clay with lias fossils, as near Banff, are more probably drifted. So also the greensand and chalk-flints spread over the rising ground from Peterhead to Cruden-noticed and collected in 1834 by the late Dr Knight of this university-are apparently detrital masses. Their number, however, and state of preservation, show that strata of this age probably once existed here in situ, and perhaps they may still occur below the waters of the North Sea. I formerly noticed the analogy of these deposits to those in the south of Sweden, where lias rests on gneiss, and is covered by chalk; but Flamborough Head is the nearest point where the chalk is now known in situ.

Last of all are the great detrital masses of the drift or boulder-clay. This forms two very marked divisions, evidently formed under very opposite conditions of the land. 1st, The lower boulder-clay, composed of thick beds of firm, brown or gray clay, full of large striated stones, some of them several feet or yards in diameter, and evidently deposited in an arctic sea, round the shores of an ice-clad land rapidly sinking in the waters. Glaciers, as the striæ they have left on the rocks testify, must then have covered our mountains, and floating icebergs filled our ocean. Above this deposit are, 2d, Loose, distinctly stratified, sands and gravels, with rounded water-worn stones. These are clearly a portion