hedrons having great transparency, very definite form, and from several millimetres to one centimetre in length.

2. Chloride of lead, in needles and cubes, slightly yellowish, of very perfect form.

3. Sulphate of lead, in cuneiform octahedrons, much modified; precisely resembling in form the crystallised sulphate of lead of Anglesea.

4. Chlorosulphate in needles.

5. Basic chloride, in microscopic crystals, disseminated here and there throughout the whole product.

6. Sulphuret of copper, black, without any appearance of crystallisation.

The whole of these substances covering the piece of galena gave it the appearance of a specimen from a mineral vein.

In some of the vessels there were formed only chloride and chlorosulphate of lead, in others chloride and sulphate, which depended no doubt upon the proportions of the sulphate of copper and of chloride of sodium, and the density of the solutions. A Voltaic couple, formed of a piece of galena, surrounded by a plantinum wire, placed in a saturated solution of common salt and sulphate of copper, diluted with three volumes of water, give rise to the formation of á considerable quantity of crystallised chloride of lead in cubes, without any other product; they were similarly deposited, though a little larger, upon a fragment of malachite which was placed in the solu

tion.

There is no evidence in opposition to the opinion that these reactions take place in nature. In fact, the pluvial waters which reach the mineral masses and veins, formed of metallic combinations, become charged with chloride of sodium and sulphate of copper, arising from the decomposition of the cupreous pyrites; the resulting solutions, once in contact with the galena, react upon it weakly, and give rise to the various compounds described above.

Two other compounds have beon obtained, Pb O, CO2 and Ca O, CO2, by the following processes :-Into a saturated solution of carbonate of soda and carbonate of copper was introduced a plate of lend,' 4 centimes by 2, surrounded by a platinum wire, 'the whole placed in a glass vessel imperfectly closed, and left to spontaneous action for seven years. The lead gradually oxidised at the expense of the atmosphere; the oxide formed, slightly soluble in water, reacted upon, the carbonate of copper, whence resulted hydrated oxide of copper and carbonate of lead (Pb O, CO2). This was in very small crystals, covering the plate of lead, and their form appeared the same as the natural carbouate. The carbonate of lime was obtained by effecting the decomposition of the sulphate of that base, a salt slightly soluble in water, and naturally abundant, by a solution of bicarbonate of soda, a compound found in several mineral waters. A plate of Montmartre gypsum was introduced into the solution (saturated or not)

of the latter salt; it soon lost its vitreous brilliancy, and was covered with small rhombohedrons of carbonate of lime. At the moment of contact, the gypsum dissolved, and reacted immediately upon the bicarbonate of soda. There was a separation of carbonic acid, which partly remained in the solution, on account of imperfect closeness of the vessel. The formation of sulphate of soda and carbonate of lime, in such a way that the plates which successively separated from the gypsum were formed of small attached rhombohedrons, cannot be supposed as solely owing to a double decomposition. It is probable that the dissolving action of the carbonic acid plays a part in the phenomenon. These effects always present themselves with weak solutions of bicarbonate.

These facts prove two principles, by the aid of which a certain number of insoluble crystalline compounds may be produced similar to the natural ones. The first consists in slowly oxidising a body in

a solution of substances, upon which the oxide formed reacts, and whence result oxides and various crystallised insoluble compounds. The second relates to the feeble reactions which take place when a slightly soluble body is placed in contact with a solution containing several compounds, giving rise to double decomposition, in which case insoluble compounds are formed, which crystallise.-(Comptes Ren dus, Feb. 1852; Philosophical Magazine, vol. iii., No. 17, 4th Series, p. 235.)

The Ocean.

"As we descend towards the present state of things, and. lands and seas approximate to their existing relations, the geographic data become more certain. One side of the globe has, we find, its vanishing continent, the other its disappearing ocean. The northern portion of our own country presents almost the identical outline which the modern geographer transfers to his atlas, save that there is here and there a narrow selvage clipped off and given to the sea, and that while the loftier headlands protrude as far as now into the ocean, the friths and bays sweep further inland; but in the southern part of the island the map is greatly different; a broad channel sweeps outwards through the middle of the land; and the highlands of Wales, south and north, exist as a detached bold-featured island, placed half-way between the coasts of England and Ireland. I found it exceedingly pleasant to lie this day on the soft, short

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sward, and look down through the half-shut eye, as the clouds sailed slowly athwart the landscape, on an apparition of this departed sea, now in sunshine, now in shadow. Adventurous keel had never ploughed it, nor had human dwelling arisen on its shores; but I could see, amid its deep blue, as the light flashed out amain, the white gleam of wings around the dark tumbling of the whale and the grampus;" and now, as the shadows rested on it dim and sombre, a huge shoal of ice-floes came drifting drearily from the north, the snow-laden rack brushing their fractured summits, and the stormy billows chafing angrily below.

"Was it the sound of the distant surf that was in mine ears or the low moan of the breeze, as it crept through the neighbouring wood? O, that hoarse voice of ocean, never silent since time first began, where has it not been uttered! There is stillness amid the calm of the arid rainless desert, where no spring rises and no streamlet flows, and the long caravan plies its weary march, amid the blinding glare of the sand, and the red unshaded rays of the fierce sun. But once and again, and yet again, has the roar of ocean been there. It is his sands that the winds heap up; and it is the skeleton remains of his vassals-shells and fish, and the stony coralthat the rocks underneath enclose. There is silence on the tall mountain peak, with its glittering mantle of snow, where the panting lungs labour to inhale the thin bleak air, where no insect murmurs, and no bird flies, and where the eye wanders over multitudinous hill-tops that lie far beneath, and vast dark forests that sweep on to the distant horizon, and along long hollow valleys, where the great rivers begin. And yet once and again, and yet again, has the roar of ocean been there. The effigies of his more ancient denizens we find sculptured on the crags, where they jut from beneath the ice into the mist wreath; and his later beaches, stage beyond stage, terrace the descending slopes. Where has the great destroyer not been, the devourer of continents, the blue foaming dragon, whose vocation it is to eat up the land? His icefloes have alike furrowed the flat steppes of Siberia and the rocky flanks of Schehallion; and his nummulites and fish lie embedded in great stones of the pyramids, hewn in the times

of the old Pharaohs, and in rocky folds of Lebanon still untouched by the tool. So long as ocean exists, there must be disintegration, dilapidation, change; and should the time ever arrive when the elevatory agencies, motionless and chill, shall sleep within their profound depths, to awaken no more, and should the sea still continue to impel its currents and to roll its waves, every continent and island would at length disappear, and again, as of old, when the fountains of the great deep were broken up,'

'A shoreless ocean tumble round the globe.'

"Was it with reference to this principle so recently recognised, that we are so expressly told in the Apocalypse respecting the renovated earth, in which the state of things shall be fixed and eternal,' that there shall be no more sea?' or are we to regard the revelation as the mere hieroglyphic, the pictured shape, of some analogous moral truth? Reasoning from what we know,'-and what else remains to us? an earth without a sea would be an earth without rain, without vegetation, without life, a dead and doleful planet of waste places, such as the telescope reveals to us in the moon. And yet the ocean does seem peculiarly a creature of time,— of all the great agents of vicissitude and change, the most influential and untiring; and to a state in which there shall be no vicissitude and no change, in which the earthquakes shall not heave from beneath, nor the mountains wear down and the continents melt away-it seems inevitably necessary that there should be no more sea.'

"But, carried away by the speculation, I lag in my geological survey."

So writes a remarkable man, the eloquent Hugh Miller, in his "First Impressions of England and its People."

1. On the Structure of Ice. 2. Rapid Evaporation of Snow and Ice. 3. Dryness of Arctic Air.

1. Structure of Ice.

With regard to the progress of the seasons, the "Indian summer," as it is called, brought us three weeks of fine weather after our arrival in September. The centre of Bear

Lake usually remains open till late in December, but by the middle of October the bays and straits are frozen across. As the structure of ice has of late years attracted the attention of speculative geologists, principally in connection with the movements of glaciers, I am induced to mention here a few facts which intruded themselves on my observation during my residences in the fur countries.

The first step in the freezing of rivers in this rigorous climate, after the water has been cooled down to 32° by a succession of cold weather, is the formation of somewhat cirenlar plates of ice, six or eight inches in diameter. These drift for a time with the current, until they have become numerous enough to cover the surface of the water, when they are arrested in a narrow part of the river, or by any slight obstacle, and speedily adhere to each other, after which the interstices between the circles fill rapidly with crystals that bind all firmly together. The sheet of ice thus produced is at first nearly opaque; but when, in the course of a day or two, it has acquired the thickness of a few inches, it becomes transparent, and remains so until a fall of snow has obscured the surface. In unsheltered lakes the wind drifts the snow to the beach, and would perhaps keep the ice clean for great part of the winter, were it not that in certain hygrometric conditions of the atmosphere small starry tufts of most beautiful tabular and latticed crystals are deposited at short intervals on the ice, and freeze firmly to it. In a dry atmosphere, these crystals evaporate again, but should a fall take place of the fine dust-like snow, which is the most common kind in high latitudes, they serve to detain it until it consolidates, so as to resist the wind. It is rare, however, for the snow to lie more than a foot deep on any of the large lakes, unless where it has drifted under the lee of piled-up slabs of ice, or of rocks, islands, or other shelter.

During winter, the ice receives an increase of thickness from beneath, and at the same time evaporates above; the latter process going on with a rapidity that would scarcely be credible to one ignorant of the extreme dryness of the air in an arctic winter. The ice acquires a thickness of from 4 to 8 feet, according to the severity of the season, the depth of