give rise to dense fogs. A sudden fall of temperature is regarded by sailors as an indication of their approach to an iceberg, and a warning to be on the outlook.

But icebergs are not formed in the open sea, where they float until they are entirely melted. To reach their birthplace, we must travel to the cold regions which surround each pole. In North Greenland, for example, the country is covered with ice, which creeps slowly down the slopes and gathers in the valleys into wide and deep masses, which not only come down to the sea-level, but actually push their way out to sea in vast walls of ice, rising three hundred or four hundred feet above the water, and stretching, sometimes, for sixty miles along the coast.

From time to time, portions of these great tongues of ice break off and float out into the open sea. These are icebergs. They consist, therefore, not of frozen sea-water, but of true land-ice. Each berg which may be met with, floating and melting far away in mid-ocean, had its origin among the snows of the Polar lands.

Since so large a proportion of an iceberg is under water, we may expect to find that these floating masses are comparatively little influenced by the winds and waves, which touch only their upper parts. The larger bergs move with the ocean currents or drifts in which so much of their substance is immersed. Hence, they may sometimes be seen moving steadily and even rapidly along, right in the face of a strong gale.

So long as the icebergs sail over deep water, they move freely about as the currents or winds may drive them. But when they get into shallow

enough water to allow their bottoms to grate along the sea-floor, they tear up the mud or sand there, until at last they are stranded. The coast of Labrador is often fringed with such stranded bergs, some so small as to be driven to the beach, others so large as to run aground while still a good way from the shore. Chill fogs, consequently, hang over that desolate region all through the summer.

Spell and pronounce :-Atlantic, Antarctic, Pacific, American, traversing, continent, infinitely, pinnacles, cascades, polar, completely, indication, Labrador, birthplace, and desolate.

LESSON LXIII.

eon tĭn'u oùs, unbroken; with- de tăched', separated; unfas

Besides the icebergs, two other kinds of ice are found on the sea in high latitudes, both derived from the freezing of the water of the sea itself. As voyagers advance into the narrow seas about the poles, they encounter great sheets of ice, which, at first in irregular, scattered fragments, become larger in size and more continuous in extent, until, at last, the whole expanse of the sea, as far as the eye can reach, is covered with ice.

This is known as floe-ice, or field-ice, and is due to the freezing of the surface water of the sea during the intense frost of Polar winters.

When the sea-water freezes, the salt is left behind by the ice, which, except for the little salt vesicles entangled in it, is fresh, and when thawed, quite drinkable. In early summer, the ice-field, or sheet of ice, which, stretching outward from the land, may be regarded as continuous for hundreds of miles during winter, begins to break up and float away.

If the sea remained motionless, it would, by the end of winter, be covered with a sheet of ice about eight feet thick. But, owing to the pressure arising partly from the movements of tides and currents in the water, partly from changes of temperature and atmospheric pressure, including winds and storms, the ice-sheet is liable to continual disruption.

Cracks are formed abundantly through it, and portions are squeezed up or broken into innumerable huge fragments, which are pushed over each other until the frozen sea becomes like a heap of ruins. And these movements are accompanied with sharp reports, as of cannon, and with loud, growling noises, as if some monsters of the deep were engaged below in fierce and angry warfare.

In consequence of the breaking up of the vast sheet of ice, openings are formed in which the unfrozen water can be seen, until it is fast bound in ice by the cold. These water-channels or lanes, between the separated fragments, are the passages by which vessels make their way through the icepack. But as the great sheets are carried against each other in the general movement, it sometimes

happens that a ship is caught between them, and pushed up on the floe, or crushed so effectually that it goes to the bottom as soon as the fragments of ice separate again.

Except where piled in heaps by pressure, which breaks up its surface as well as its outer edges, floe-ice occurs in level sheets, the surface of which rises but little above the level of the sea. It never rivals the height and grandeur of true icebergs, though it covers a much wider space of sea. Nor does it travel so far from the regions of its birth. When the ice-field breaks up in summer, the portions next the land may remain there, and of these, indeed, some parts may continue unmelted for generations. But other parts farther from shore, and sometimes many hundreds of square miles in extent, are loosened and carried away by the sea-currents which drift from the pole. Vessels frozen into the ice-fields have in this way been carried many hundreds of miles, until disengaged by the disruption and thawing of the ice.

Some of the icebergs from Greenland, however, travel much farther south, and may be met with, now and then, even as far south as 37° latitude; that is, about the same parallel as Richmond in Virginia, and Cape St. Vincent in the south of Spain.

THE ICE-FOOT.

When the sea freezes along the margin of the land, as it does in a remarkable way in North Greenland, it forms a cake of ice, which, rising with the tide, is frozen to the shore. By degrees, a shelf of ice, called the ice-foot, rising from twenty to thirty feet above the general level of the floe, and having a width of one hundred and twenty

feet or more, forms along the coast and clings to

it all winter.

Immense quantities of earth and stones, dislodged from the coast cliffs by the severe frost of the Arctic winter, fall upon the ice-foot, so that its surface becomes, in some places, a field of rubbish, which completely covers and conceals the ice underneath. When the summer storms come, this shore-terrace of ice is broken up, and large pieces of it, laden with the waste of the cliffs, are floated away out to sea, there to join the fleets of bergs and broken sheets of floe-ice.

Some portions are driven ashore again, others are caught and frozen fast into the floe-ice of next winter, while others succeed in escaping into the more open sea, where they gradually melt and tumble their load of earth and stones on the seabottom.

GROUND-ICE.

Floe-ice and the ice-foot are formed by the freezing of the surface of the sea. There is yet another way in which some of the ice of the sea takes its origin; namely, by the freezing of the water lying on the sea-bottom. This is known as ground-ice.

It is probably formed only in inclosed and shallow seas and inlets, and is of little consequence compared with the thick and wide sheets of floeice. It is well known in the Baltic Sea. In still weather, before the surface of that sea is frozen, little thin cakes of ice may be observed floating about, sometimes with portions of sand or scattered pebbles imbedded in them. These are formed on the bottom, from which they break away and rise to the surface.