The areas marked out by the contour-lines of depth are now estimated as follows: -- Between the shore and 100 fms., 7,000,000 sq. Not only are the continental slopes the seat of many deposit-slips and seismic disturbances, but Mr.
Benest has given good reasons for believing that underground rivers sometimes enter the sea at depths beyond 100 fathoms, and there bring about sudden changes in deep water.
The recognition of oceanography as a distinct branch of science may be said to date from the commencement of the Challenger investigations.
The fuller knowledge we now possess about all oceanic phenomena has had a great modifying influence on many general conceptions as to the nature and extent of those changes which the crust of the earth is now undergoing and has undergone in past geological times.
Wireline sounding had been invented by Sir William Thomson, steel cable for dredging operations and other oceanographic purposes had been introduced, and great strides had been made in biological, chemical, geological and physical oceanography. A great many sciences were enriched by a grand accumulation of new facts.
Dominating this new science of the sea was Sir John Murray of the Challenger Expedition. Large collections were sent and brought home, and were subsequently described by specialists belonging to almost every civilised nation.The deep soundings are scattered over the different ocean-basins in varying proportions, being now most numerous in the North Atlantic and South-west Pacific, and in these two regions the contour-lines of depth may be drawn in with greater confidence than in the other divisions of the great ocean-basins. Valdivia in the Atlantic, Indian, and Southern Oceans have not caused very great alteration in the position of the contour-lines on the Challenger maps, if we except one occasion in the South Atlantic when a depth of 2000 fathoms was expected and the sounding-machine recorded a depth of only 536 fathoms, and again in the great Southern Ocean when depths exceeding 3000 fathoms were obtained in a region where the contour-lines indicated between 10 fathoms.It may be pointed out that 659 soundings taken quite recently during cable surveys in the North Atlantic, although much closer together than is usually the case, and yielding much detailed information to cable engineers, have, from a general point of view, necessitated but little alteration in the contour-lines drawn on the Challenger bathymetrical maps published in 1895. This latter discovery suggests that the great depth recorded by Ross to the south-east of South Georgia may not be very far from the truth. From these results it appears that considerably more than half of the sea-floor lies at a depth exceeding 2000 fathoms, or over two geographical miles.I have redrawn the several contour-lines of depth in the great ocean-basins, after careful consideration of the most recent data, and these may now be regarded as a somewhat close approximation to the actual state of matters, with the possible exception of the great Southern and Antarctic Oceans, where there are relatively few soundings, but where the projected Antarctic Expeditions should soon be at work. It is interesting to note that the area within the 100-fathom line occupies 7,000,000 square geographical miles, whereas the area occupied by the next succeeding 900 fathoms (viz., between 1 fathoms) occupies only 10,000,000 square geographical miles.On the whole it may be said that the general tendency of recent soundings is to extend the area with depths greater than 1000 fathoms and to show that numerous volcanic cones rise from the general level of the floor of the ocean-basins up to various levels beneath the sea-surface. (or 7% of the sea-bed) ” 100 ” 1000 ” 10,000,000 ” ” (or 10% ” ” ) ” 1000 ” 2000 ” 22,000,000 ” ” (or 21% ” ” ) ” 2000 ” 3000 ” 57,000,000 ” ” (or 55% ” ” ) Over 3000 fathoms 7,000,000 ” ” (or 7% ” ” ) 103,000,000 sq. This points to a relatively rapid descent of the sea-floor along the continental slopes between 1 fathoms, and therefore confirms the results gained by actual soundings in this region, many of which indicate steep inclines or even perpendicular cliffs.Compared with this shallow-water region, the soundings in deep water beyond the 100-fathom line are much less numerous; each year, however, there are large additions to our knowledge.Within the last decade over ten thousand deep soundings have been taken by British ships alone.Again, the relatively large area covered by the continental shelf between the shore-line and 100 fathoms points to the wearing away of the land by current and wave action.On the Challenger charts all areas where the depth exceeds 3000 fathoms have been called “Deeps,” and distinctive names have been conferred upon them.This is particularly important for freelance writers whose success depends on the number of people who open and read their essays, articles, and so on.Before you start writing a title for your essay, it is always useful to know more about qualities that every headline should have.