The European section is limited—the rivers being few in number, and of no great importance. The principal are the Onega, Dwina, and Mezen, which enter the White Sea, and the Petchora, which falls into the Arctic Ocean.
The American section comprises one large river, the Mackenzie, and several smaller ones, such as the Colville, Coppermine, and Great Fish River. The Mackenzie proper flows north from the Great Slave Lake, and, like the Colville, falls directly into the Arctic Sea. The Coppermine flows into Coronation Gulf, and the Great Fish River into the channel between Boothia and King William's Land. All these rivers discharge the collected drainage of a vast number of fresh water lakes and swamps, connected together by numerous canal-like streams, such as the Slave River and others.
The best known currents of the Arctic Ocean are those that flow south on either side of Greenland, and, be ing deflected to the west, unite off Cape Farewell, and pro ceed south along the coast of Labrador as the great Arctic Current. Off the Grand Banks of Newfoundland this cold drift from the north meets the warm current of the Gulf Stream from the south ; thence to Cape Hatteras we have the remarkable phenomenon of two contiguous currents, one cold and the other warm, flowing in exactly opposite direc tions—the former south-west, the latter north-east. The cold current finally sinks under the Gulf Stream, and enters the Gulf of Mexico as an under-current. " The Arctic Cur rent thus replaces the warm water sent through the Gulf Stream, and modifies the climate of Central America and the Gulf of Mexico, which, but for this beautiful and benign system of aqueous circulation, would be one of the hottest and most pestilential in the world." The north-easterly pro longation of " the Gulf Stream "—as the northerly set of the North Atlantic beyond the British Isles and Norway is some times called—seems to carry comparatively warm water right into the Arctic basin, due north between East Greenland and Spitzbergen, and eastwards between Nova Zembla and Franz Joseph Land. A branch of the latter is probably continued eastwards along the Siberian coast, and reinforced, more espe cially in summer, by the vast quantities of comparatively warm water discharged by the then swollen rivers of Siberia, moves towards Behring's Strait, where it is deflected to the north-east by the strong, warm current which sets into the Arctic from the Pacific through that strait. The united stream then flows north-east towards Parry Islands, and may probably be continued, through Melville Sound and Barrow Strait, into Baffin Bay—thus merging into the great Arctic Current, which pours south through Davis Strait. The pro bability of an open sea in the immediate neighbourhood of the Pole necessarily depends on the existence of a powerful warm under-current rising there to the surface. A continuous series of observations on the currents, &c., at accessible points within the partially known belt (70° to 80° N. lat.), would undoubtedly ultimately conduce to a far more successful re search further north, than any spasmodic attempt to force a passage to the Pole without sufficiently numerous and recent data on which the best method of procedure could be based.
As regards its depth, the Arctic Ocean is, with one exception, nowhere much deeper than 1000 fathoms. The long slopes of Northern Asia and America indicate a continuous belt of shallow water, which the numerous islands further north prove to be continued in parts as far as 80° and 83° north latitude. The deepest known portion is the basin lying between the Arctic Circle and the parallel of 80° N., and from Spitzbergen and Norway on the east, to Greenland on the west. The Norwegian Expedition, on board the Voringen, obtained in August, 1876, a sounding of 1,800 fathoms between Iceland and Norway, and the whole basin has an average depth of over 1,000 fathoms. From the centre of this basin the precipitous cliffs of the volcanic island of Jan Mayen rise nearly 7,000 feet above the level of the se& The depth near the ice-barrier which checked the progress of Sir George Mires was only 72 fathoms.
Among the remarkable features of the Arctic regions are the perpetual daylight in summer and constant darkness in winter, due to the inclination of the earth's axis to the plane of its orbit. The long winter night is occasionally relieved by the magnificent phenomenon, the Aurora Borealis, which is thus graphically described by Mrs. Somerville :—
" The Aurora is decidedly an electrical (or, more strictly speaking, a magneto-electrical) phenomenon. It generally appears soon after sunset in the form of a luminous arc, stretching more or less from east to west, the most elevated point being always in the magnetic meridian of the place of the observer; across the arc the corusca tions are rapid, vivid, and of various colours, darting like lightning to the zenith, and at the same time flitting laterally with incessant velocity. The brightness of the rays varies in an instant; they sometimes surpass the splendour of stars of the first magnitude, and often exhibit colours of admirable transparency,—blood-red at the base, emerald green in the middle, and clear yellow towards their extremity. Sometimes one and sometimes a quick succession of luminous currents run from one end of the arc or bow to the other, so that the rays rapidly increase in brightness : but it is impossible to say whether the coruscations themselves are actually affected by a horizontal motion of translation, or whether the more vivid light is conveyed from ray to ray. The rays occasionally dart far past the zenith, vanish, suddenly re-appear, and, being joined by others from the arc, form a magnificent corona or immense dome of light. The segment of the sky below the arc is quite black, as if formed by dense clouds; yet M. Struve is said to have seen stars in it, and so it would appear that the blackness of which several observers speak must be the effect of contrast. The lower edge of the arc is evenly defined; its upper margin is fringed by the coruscations, their convergence towards the north, and that of the are itself, being probably an effect of perspective." The almost constant precipitation of snow covers the whole of the Arctic highlands to an enormous depth, and the partial liquefaction in the short summer, and the accu mulation in the long valleys and along the steep slopes of Greenland, &c., results in the formation of vast glaciers,' the lower end of which is gradually pushed out into the sea. Violent storms and other causes result in the breaking off of the projecting portions, which are thus free to move off with the winds or currents. These floating bodies of ice are the icebergs, so dangerous to navigation not only in the Arctic Seas, but also in the North Atlantic as far south as the 40th parallel. On the breaking up of the continuous winter-ice, immense numbers of these icebergs, or ice-moun tains, are carried south by the Arctic current. Some are 250 to 300 feet high above the sea level, and as there must be about eight times as much below the surface of the water, the total height of a berg 300 feet above the surface is about 2,400 feet, hence they are often seen stranded a long distance from the shore.' Masses of ice, from a mile to fully 100 miles across, and from ten to fifty feet thick, are frequently met with in motion. Portions detached from an icefield, as these continuous masses are called, form the floes or and the irregular elevations on an icefield due to lateral pressure form the greatest obstacles to Arctic exploration, and are known as hummocks. The annual disruption of the great ice fields formed during the intensely cold winter, results in the breaking off of innumerable masses of floe-ice, and in the separ ation of the larger 'fields.' Through the openings thus formed vessels push way to the open water beyond. Sometimes, however, the masses on either side close together, in which case the unfortunate vessel is thrown up on the ice, or held fast and drifted along with the ice-pack, and not unfrequently crushed and sunk.
[Animal life in the Arctic regions is abundant up to a very high latitude, musk-oxen, hares, and ptarmigans being found even as far north as 82°. The reindeer, musk-ox, Arctic fox, Arctic bare, wolf, and bear are also found, besides an enormous number of birds, including the guillemot, auk, puffin, merganser, goosander, smew, gull, eider-duck, wild swan, ptarmigan, &c. The seas are frequented by vast numbers of cod, capelin, halibut, dolphin, &c., and the right whale, narwhal, various kinds of seals, and the walrus. During the summer months numbers of whaling vessels frequent the Polar Seas. Vast numbers of seals, &c., are also caught, and a large trade is carried on at the Danish settle ments with the Esquimaux ; furs (bear, fox, seal, &c.) being ex changed for European goods.]