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ANALYSES OF Books.
Memoirs of the Wernerian Natural History Society. Vol. II.
Part II. For the Years 1814, 1815, 1816. This part contains the following papers :
I. On the Greenland, or Polar Ice. By W. Scoresby, Jun. Esq. M.W.S.-Mr. Scoresby has been in the habit of going annually to the Greenland seas, for these many years past, as a whale fisher. Being a man of excellent abilities, of good education, and a zealous observer, he has collected a vast number of curious and important facts, which must, when they are given to the public, contribute materially to the improvement of meteorology, for the weather in the polar regions must influence materially the winds and currents of the Atlantic and Pacific Oceans; which, in their turn, exercise a material influence upon the continents which lie on either side of them. In our report of the proceedings of the Wernerian Society, vol. vi. p. 142, &c. we gave an account of the present paper ; but as the subject is very curious in itself, and particularly interesting at the present moment, when the public attention is drawn to the two voyages of discovery lately made to the arctic regions, we are induced to give an analysis of it, even at the risk of repetition.
The whalers have distinguished the polar ice by a variety of names according to its state. A large ice plain, extending further than the eye can reach, is called a field. When a field, in consequence of a heavy swell
, is broken into pieces, not exceeding 40 or 50 yards in diameter, which remain in close contact, so that they cannot be seen over from the ship's mast, they are termed a pack. When the collection of pieces can be seen over, and when it assumes a circular, or polygonal form, it is called a patch. When it is long and narrow, it is called a stream. Pieces of very large dimensions, but smaller than fields, are called floes. Small pieces which break off and are separated from the larger masses by the effect of attrition, are called brash ice. Ice is said to be loose, or open, when small pieces are so far separated as to allow a ship to sail freely among them. This has likewise been called drift ice. A hummock is a protuberance raised upon any plane of ice above the common level ; it often attains the height of 30 feet, or upwards. A calf is a portion of ice depressed by the same means as a hummock is elevated. Any part of the upper surface of a piece of ice, which comes to be immersed beneath the surface of the water, is called a tongue. A bight is a bay, or sinuosity, on the border of any large mass or body of ice.
When the ice is porous, white, nearly opaque, but having a
greenish shade of colour, it is considered by the whalers as formed by the congelation of sea-water, and called salt water ice. When this ice is thawed, it sometimes yields fresh water, and sometimes brackish water. The specific gravity of this ice, according to Mr. Scoresby, is 0.873.
The name fresh water ice is applied to ice which has a black appearance while floating in the sea, but a beautiful green hue and transparency when removed into the air. Its transparency is usually interrupted by numerous small, pear-shaped air-bubbles. When formed into convex lenses, it collects the sun's rays into a focus, and sets fire to gunpowder, &c. precisely as a glass lens would do. Its specific gravity, according to Mr. Scoresby, is 0.937.
It has been conceived by many, that the ice which covers the polar seas has its origin from the land ; but Mr. Scoresby is of opinion that the vicinity of land is not necessary for the formation of ice. He has seen the sea freeze at a distance from land, both when smooth and when agitated by the wind; and he describes the appearances which take place in both cases. He conceives that, during the summer months, the polar ice splits, and one portion separates to a distance from the other. In winter, the interval between these two portions freezes, and becomes covered
This snow is melted during the ensuing summer, and the pond of water, thus formed upon the ice, freezing the ensuing winter, constitutes a field of ice.
Fields have a constant tendency to drift to the south-west. This occasions the destruction of many, whose place is supplied by others from the pole. Fields sometimes acquire a circular motion of three or four miles an hour. When two fields moving different ways meet, they act upon each other with prodigious energy, breaking each other in pieces, and piling up the fragments to a great height. When ships are interposed between two fields, in such a case, the consequence is alarming, and often destructive.
The term iceberg is commonly applied to those immense bodies of ice situated on the land, filling the valleys between high mountains, and generally exhibiting a square perpendicular front towards them. They recede backwards inland to an extent never explored. Large pieces may be separated from these icebergs in the summer season. These masses, floating in the sea, still retain the name of icebergs, ice islands, or ice mountains. In height, above the surface of the sea, they may be 100 feet, or more, and below the surface, 100 yards, or more; while their diameter varies from a few yards to some miles. They abound in Davis's Strait ; but are few in number and small in size off the coast of Spitzbergen. On that account, Mr. Scoresby thinks that they rather originate in sheltered bays of the land than from land icebergs. They occur also at some hundred miles' distance from land towards the north. The perpetual accumulation of snow, &c. from the atmosphere during a long succession of centuries, is sufficient, in the author's opinion, to account for the existence of the largest ice mountains than can be supposed to exist.
The icy barrier at the return of spring exhibits the following general outline. After doubling the southern promontory of Greenland, it advances in a north-easterp direction along the east coast enveloping Iceland as it proceeds, until it reaches John Mayne's Island, in latitude 71° N., longitude about 540 W. Passing this island on the north-west, but frequently enclosing it likewise, it then trends a little more to the eastward, and intersects the meridian of London in the 71st or 720 degree of latitude. Having reached the longitude of 6, 8, or perhaps 10 degrees east in the 73d or 74th degree of north latitude, it suddenly stretches to the north, sometimes proceeding on a meridian to the latitude of 80° ; at others, forming a deep sinuosity, extending two or three degrees to the northward, and then south-easterly to Cherry Island, which having passed, it assumes a direct course a little south of east, until it forms a junction with the Siberian, or Nova Zemblan coast. When the ice at the extremity of this remarkable bay occurs so strong and so compact as to prevent the approach to the shores of Spitzbergen, and the advance northward beyond the latitude of 75', or 76°, it is said to be a close season, On the contrary, it is called an open season when an uninterrupted navigation extends along the western coast of Spitzbergen to Hackluyt’s Headland. It is about latitude 80° that the haunt of the whale occurs. The great object of the whaler is to get into that situation, and much dexterity and intrepidity are necessary to enable him to get as speedily as possible into the proper fishing latitude. The loose ice which opposes his passage northwards has disappeared by the middle of June, when he has to return home.
II. On the Mineralogy of the Read Head, in Angusshire. By the Rev. John Fleming, D.D. F.R.S.E.-This district, which may be considered as the termination of the great valley of Strathmore, consists partly of alluvial beds and partly of floetz rocks. The alluvial beds consist of sand and gravel, and may be seen along the banks of the Brothick and the Lunan, two small rivers which run into the sea at this place. The beds of sand are parallel to each other, but they dip in some places at an angle of 24°. Dr. Fleming adduces this fact as a demonstration that the Huttonian axiom, that beds deposited at the bottom of a liquid must be horizontal, is not always true.
The floetz rocks in this district are the old red sandstone, which skirts the Grampians on both sides, and runs from the east to the west sea. Dr. Fleming considers the hills of Kinnoul and Moncrief, the Ochil Hills, and Arthur's Seat, as belonging to the old red sandstone, and constituting beds in it. If this opinion, which was advanced by. Professor Jameson in a paper
published some years ago in the Annals of Philosophy, be correct, it will follow from it that most of the rocks supposed hitherto. to be peculiar to the newest floetz trap formation, belong to the old red sandstone, and constitute subordinate beds in it. Thus if East Lothian consists of old red sandstone, the porphyry slate of North Berwick law, and Traprene law, and the floetz trap rocks of Dunbar, must constitute beds in the sandstone. This would probably be made out in a satisfactory manner by travelling along the south coast of the Frith of Forth from Prestonpans to Dunbar, as the rocks are exposed for the greatest part of that way.
III. Description and Analysis of a Specimen of Native Iron found at Leadhills. By Mr. H. M. Dacosta, M.W.S.–The specimen was found associated with galena, and was discovered by the workmen from its resisting the blows of a hammer. It possessed the external characters of iron, and was found composed of Iron.
1.0 Loss, chiefly sulphur ..
IV. Mineralogical Observations in Galloway. By Dr. Grierson. There are three different granite districts in Galloway. Dr. Grierson formerly gave an account of the middle, or Dee district, in a paper published in a former volume of the Annals of Philosophy. The object of this paper is to give an account of the western, or Doon granite district. This district lies between Loch Doon and Loch Dee, and probably extends eight miles in length and four miles in breadth. It is covered on all sides by a rock, to which the author has given the name of compact gneiss. This
gneiss rock can be traced sometimes for a mile, and sometimes only for a few hundred yards. Greywacke always covers it; at least, Dr. Grierson no where found the greywacke in contact with the granite. Fragments of the gneiss are frequently met with in the granite. It contains likewise numerous beds of felspar porphyry.
V. Lithological Observations on the vicinity of Loch Lomond. By Dr. Macknight. The rocks round Loch Lomond are mica slate, which continues to Ben Lomond, which is itself composed of it. The mica slate contains thick beds of felspar porphyry
greenstone. Immediately to the south of Ben Lomond, the clay slate rocks commence. At Luss and Camstradden, they are quarried for roofing slate. The clay slate is followed by greywacke and greywacke slate, and these transition rocks are followed by the old red sandstone.
I had an opportunity last autumn of examining a small portion
of the east bank of Loch Lomond, near Buchanan House, just where the greywacke terminates. The next rock is a limestone, which is probably transition, though it does not possess the usual characters of that kind of rock. The limestone is succeeded by á very coarse gravel stone, composed almost entirely of rounded quartz pebbles, seemingly cemented by a quartzy matter. This rock is obviously a modification of the old red sandstone, which a little to the south appears in its usual characters. This part of the Grampian agrees in its structure with every other cross section of these mountains which I have had an opportunity of examining
VI. Description of Ravensheugh. By Dr. Macknight.- This is the name given to a point of the coast included in the Earl of Haddington's pleasure-grounds at Tyningham, about six miles north-west of Dunbar. It consists of a set of beds forming a ock, which exposes a precipitous front to the sea, about 40 or 50 feet in height. This rock is composed of floetz trap beds reposing on old red sandstone. The trap beds consist of basalt, red and green trap tuff
, impregnated with lime, clinkstone, and porphyry slate. The curious circumstance attending it is, that the beds of sandstone over which this floetz trap rock lies, seems to run beneath the basalt in every direction, assuming the form of a vast cup, or cavity, filled with the floetz trap. This depression Dr. Macknight accounts for, by supposing that the floetz trap was deposited upon the sandstone before this last rock was completely deposited. Hence it would, he thinks, squeeze down the sandstone, and cause the depression which exists.
If this explanation be well founded, the specific gravity of the sandstone below the floetź trap would be greater than at à distance from it.
VII. Hints regarding the Coincidence which takes place in the Pressure of the Atmosphere at different Latitudes, and at nearly the same Time. By the Right Hon. Lord Gray, F.R.S. Lond. and Edin. &c.--His Lordship shows, by a set of curves, exhibiting the march of the barometer, during two years, at Gordon Castle, Kinfauns Castle, Greenwich Observatory, and Plymouth, that the rise and fall was nearly simultaneous at all these places. He thinks that this will hold nearly from the pole to the equator, and is exceedingly anxious to have the means of verifying his conjecture by observations made in the southern hemisphere.
(To be continued.)