The continental area is on one side of the sphere and the oceanic on the other.
Wide areas, giving rise to oceanic depressions and leaving the continents protuberant; the other, folding along comparatively narrow belts, giving rise to mountain ranges.
The Trachylinae, on the other hand, are above all oceanic forms, and have no polyp-stage, and hence there is typically no alternation in their life-cycle.
The general scheme of oceanic circulation was made out prior to 1910.
The Pacific has few islands; the oceanic islands are volcanic, and coral formations are of course scanty.
Where the central oceanic buckle attains the water-line we have our oceanic islands, seen in our type ocean, as St Helena and the Azores.
The nature of the change of temperature with depth below 2500 fathoms is entirely dependent on the position of the sub-oceanic elevations, for the rises and ridges act as true submarine watersheds.
The movement of emigration may be divided into two currents, temporary and permanentthe former going chiefly towards neighboring European countries and to North Africa, and consisting of manual laborers, the latter towards trans-oceanic countries, principally Brazil, Argentina and the United States.
Oceanic islands are divided according to their geological character into volcanic islands and those of organic origin, including coral islands.
The flora falls naturally into three great divisions: that of the Amazon basin where exceptional conditions of heat and moisture prevail; that of the coast where heat, varying rainfall, oceanic influences and changing seasons have greatly modified the general character of the vegetation; and that of the elevated interior, or sertao, where dryer conditions, rocky surfaces, higher sun temperatures and large open spaces produce a vegetation widely different from those of the other two regions.
Upon the denuded edges of the Scotland beds lies the Oceanic series.
The Oceanic series is generally overlaid directly, and unconformably, by coral limestones; but at Bissex Hill, at the base of the coral limestones, and resting unconformably upon the Oceanic series, there is a Globigerina marl.
The honour of first sounding really oceanic depths belongs to " Egeria," " Waterwitch," " Dart," " Penguin," " Stork," Sir James Clark Ross, who made some excellent measurements and " Investigator."
Large angles of slope may, however, occur on the flanks of oceanic islands and the continental borders.
A definite terminology for the larger forms of sub-oceanic relief was put forward by the International Geographical Congress at Berlin in 1899 and adopted by that at Washington in 1004.
The continental shelves include not only the oceanic border of the continents but also great areas of the enclosed seas and particularly of the fringing seas, the origin of which through secular subsidence is often very clearly apparent, as for instance in the North Sea and the tract lying off the mouth of the English Channel.
The greatest of the intercontinental seas, the Arctic, comes nearest to oceanic conditions in the extent and depth of its depressions.
Buchan, " Specific Gravities and Oceanic Circulation," Trans.
Richard, L'Oceanographie (Paris, 1907); List of Oceanic Depths and Serial Temperature Observations, received at the Admiralty in the year 1888 (et seq.) from H.M.
Many of the oceanic islets are composed of coral limestone, which in this way becomes phosphatized; others are igneous, consisting of trachyte or basalt, and these rocks are also phosphatized on their surfaces but are not so valuable, inasmuch as the presence of iron or alumina in any quantity renders them unsuited for the preppration of artificial manures.
Hence the proportion of purely oceanic area to the total area is greater in the Pacific than in the Atlantic, the supply of detritus being smaller, and terrigenous deposits are not borne so far from land.
Next, dependent on the inclination of the earths axis, is the division of the planetary year into the terrestrial seasons, with winter and summer changes of temperature, wind-strength and precipitation: these seasonal changes are not of the restrained measure that is characteristic of the oceanic southern temperate zone, but of the exaggerated measure appropriate to the continental interruptions of ~the northern land-and-water zone, to which the term temperate is so generally inapplicable.
The "Mediterranean region," as a geographical unit, includes all this area; the Black Sea and the Sea of Marmora are within its submerged portion, and the climate of the whole is controlled by the oceanic influences of the Mediterranean Sea.
The origin and development of these conditions, in islands so distinctly oceanic as the Galapagos, have given its chief importance to this archipelago since it was visited by Darwin in the "Beagle."
The terrace closest to the land, known as the continental shelf, has an average depth of 600 ft., and connects Australia, New Guinea, and Tasmania in one unbroken sweep. Compared with other continents, the Australian continental shelf is extremely narrow, and there are points on the eastern coast where the land plunges down to oceanic depths with an abruptness rarely paralleled.
Newfoundland, the West Indies, and the Falklands, and the chief oceanic islands are the Azores, Madeira, the Canaries, the Cape Verde Islands, Ascension, St Helena, Tristan da Cunha and Bouvet Island.
This order, containing the typical oceanic medusae, is divided into two sub-orders.
Thus the best approximation to the average depth of the ocean is little more than an expert guess; yet a fair approximation is probable for the features of sub-oceanic relief are so much more uniform than those of the land that a smaller number of fixed points is required to determine them.
The latter rise abruptly from the oceanic abysses.
The direct geographical elements are the arrangement of land and sea (continents and islands standing in sharp contrast) and the vertical relief of the globe, which interposes barriers of a less absolute kind between portions of the same land area or oceanic depression.
Oceanic islands have, as a rule, distinctive faunas and floras which resemble, but are not identical with, those of other islands in similar positions.
For narrow as are the channels between Cuba and the opposite coast of Central America, between the Bahamas and Florida, and between Grenada and Tobago, the fauna of the Antillean chain, instead of being a mixture of that of the almost contiguous countries, differs, much from all, and exhibits in some groups a degree of speciality which may be not unfitly compared with that of oceanic islands..
The Coleoptera are almost worldwide in their distribution, being represented in the Arctic regions and on almost all oceanic islands.
Russia has no oceanic possessions; her islands are all appendages of the mainland to which they belong.
Interesting relationships between the Ethiopian and Oriental, the Neotropical and West African, the Patagonian and New Zealand faunas suggest great changes in the distribution of land and water, and throw doubt on the doctrine of the permanence of continental areas and oceanic basins.
The study of the Hexapoda of oceanic islands is full of interest.
Except in the extreme north and south, and on the tops of the highest mountains, where there is no insect life as food supply, spiders are found all over the world, even in isolated oceanic islands.
The possession of silk-glands has also profoundly influenced the geographical distribution of spiders and has enabled them to cross arms of the sea and establish themselves on isolated oceanic islands which most of the orders of Arachnida are unable to reach.
The empirical data on which the hydrodynamical investigations are based are: (I) observed velocities and directions of oceanic currents and drifts; (2) salinity; (3) density; (4) temperature of the sea water in situ; (5) oceanic soundings.
Now it is probable that the main cause of oceanic circulation is the driving force of the winds upon the superficial layers of water.
Jukes-Browne and Harrison ascribe the Scotland beds to the Eocene or Oligocene period, the Oceanic series to the Miocene, the Bissex Hill marls to the Pliocene, and the coral limestones partly to the Pliocene and partly to the Pleistocene.
The former are either the extensions of oceanic depressions, e.g.
Oceanic Deposits.-It has long been known that the deposits which carpet the floor of the ocean differ in different places, and coasting sailors have been accustomed from time immemorial to use the lead not only to ascertain the depth of the water but also to obtain samples of the bottom, the appearance of which is often characteristic of the locality.
Pettersson has made a careful study of ice melting as a motive power in oceanic circulation, and points out that it acts in two ways: on the surface it produces dilution of the water, forming a fresh layer and causing an outflow seaward of surface water with very low salinity; towards the deep water it produces a strong cooling effect, leading to increase of density and sinking of the chilled layers.
The following islands may be classified as oceanic, but not with any of the three main divisions: the Bonin Islands, north of the Marianas, belonging to Japan; Lord Howe and Norfolk Islands (to New South Wales); Easter Island (to Chile); the Galapagos Islands (to Ecuador).
The following paragraphs review the oceanic islands generally, and are therefore concerned almost entirely with the central and mid-western parts of the ocean.
In1525-1527Garcia Jofre de Loyasa sailed to the Moluccas, but, like Magellan, missed the bulk of the oceanic islands.
In the oceanic islands of the Pacific three different peoples occur, who have been called Melanesians, Polynesians and Micronesians.'
That the oceanic blacks form one family there can be no doubt, and it is evidence of the immensely remote date at which their dispersion began that they have a multitude of languages often unintelligible except locally, and an extraordinary variety of insular customs: differentiations which must have needed centuries to be effected.
Codrington (Melanesian Languages) has adduced evidence to prove that Melanesia is the most primitive form of the oceanic stock-language, and that both Malays and Polynesians speak later dialects of this archaic form of speech.
One of the most obscure questions with which the ethnologist has to deal is that of the prehistoric remains which occur in different and widely separated parts of the oceanic region.
There are trans-oceanic lines to Japan and China, to the Philippines and Hawaii, and to London, Liverpool and Glasgow, by way of the Suez Canal.
Each of the larger islands has one or more ports which a local steamboat serves regularly, and Honolulu has the regular service of seven trans-Pacific lines (the American-Hawaiian Steamship Co., the Canadian-Australian Steamship Co., the Matson Navigation Co., the Oceanic Steamship Co., the Pacific Mail Steamship Co., the Mexican Oriental and the Toyo Kisen Kaisha); it is a midway station for vessels between the United States (mainland) and Australia and Southern Asia.
Those of the highest zone are remarkable for the great predominance of predaceous species and of wingless forms. In this last respect they present a striking analogy with the endemic coleopterous fauna of oceanic islands.
The proportion of salt in the water of the Caspian, though varying in different parts and at different seasons, is generally much less than the proportion in oceanic water, and even less than the proportion in the water of the Black Sea.
The order is practically cosmopolitan, with the exception of New Zealand and certain absolutely isolated oceanic islands, like the Hawaiian islands and the Azores.
Hence their tidal conditions are quite oceanic, though their salinity is usually rather lower than that of ocean water.
One geniis of Hydrometridae (Halobates) is even oceanic in its habit, the species being met with skimming over the surface of the sea hundreds of miles from land.
The Hydrometridae are a large family including the pond-skaters and other dwellers on the surface-film of fresh water, as well as the remarkable oceanic genus Halobates already referred to.
But if their origin is unknown, there is little doubt that the Melanesians were the earliest occupants of the oceanic world, possibly reaching it from Malaysia.