This takes account of - (I) the ArcticAlpine zone, including all the vegetation of the region bordering on perpetual snow; (2) the Boreal zone, including the temperate lands of North America, Europe and Asia, all of which are substantially alike in botanical character; (3) the Tropical zone, divided sharply into (a) the tropical zone of the New World, and (b) the tropical zone of the Old World, the forms of which differ in a significant degree; (4) the Austral zone, comprising all continental land south of the equator, and sharply divided into three regions the floras of which are strikingly distinct - (a) South American, (b) South African and (c) Australian; (5) the Oceanic, comprising all oceanic islands, the flora of which consists exclusively of forms whose seeds could be drifted undestroyed by ocean currents or carried by birds.
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.
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.
The natural effect of the heating of the air in summer and the cooling of the air in winter by contact with the land is largely masked in England on account of the strength of the prevailing south-westerly wind carrying oceanic influence into the heart of the country.
In1525-1527Garcia Jofre de Loyasa sailed to the Moluccas, but, like Magellan, missed the bulk of the oceanic islands.
Wide areas, giving rise to oceanic depressions and leaving the continents protuberant; the other, folding along comparatively narrow belts, giving rise to mountain ranges.
This plateau formation - the oldest geological continent of Asia - being unfit for agriculture and for the most part unsuited for permanent settlement, while its oceanic slopes have from the dawn of history been occupied by a relatively dense population, long prevented Slav colonization from reaching the Pacific. The Russians chanced to cross it in the 17th century at its narrowest and most N.
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.
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 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.