future continents than any other equal space on the globe.

Wallace, in his classical work on the Malay Archipelago, observes that the expanse of sea which divides the islands of Java, Sumatra, and Borneo from each other and from Malacca and Siam is so shallow that ships can anchor in any part of it, since it seldom exceeds 40 fathoms in depth.1

The Philippines and Celebes.-Mr. George F. Becker, in his report on the Geology of the Philippine Islands, calls attention to the many existing evidences of Pleistocene variations of level to be seen in these islands. He says: Physical evidences that the islands are rising at the present time, or have been rising within a few years, abound from one end of the group to the other. It is also clear that the amplitude of the movement has been very great.'3 The recent plains, which form the most valuable and thickly settled portion of the islands, are in large part areas of marine denudation and deposition, outer portions of the continental plateau, which have been lifted above the water-level in very recent times.'4 Further evidences of movement are recorded in the 'high terraces, as well as low ones, abundant throughout the islands. . . .' This part of Cebu must approach 2,000 feet in

1 P. 9, 1890.

2 Twenty-first Annual Report of the U.S. Survey, 1899-1900, Part iii., General Geology re Phosphate Deposits, Philippines.'

height, and is scored by a vast number of terraces, all of which are sensibly horizontal.'1

These islands, it may be here remarked, 'lie along the edge of a vast submarine precipice, or, in other words, at the very abrupt limit of the continental plateau.' Elsewhere Mr. Becker speaks of the eastern edge of the continental plateau being outlined by submarine cliffs, and a reference to the map (Pl. LXVII.) will show that the plateau on which the islands are based is not submerged more than 50 metres. Doubtless this has been largely built up by sediment. It is very instructive to see that there are deeps' in this plateau, one of which reaches no less than 3,291 metres, proving plainly, what is here so frequently insisted upon, that the sea bottom is very diversified in its topography. Nor must we lose sight of the fact that the base rock of the Philippines consists of crystalline schists, notwithstanding that volcanoes abound, so that there would be less justification here for the usual explanation, that such irregularities of bottom are due to volcanic action.

Celebes, an island lying due south of the Philippines, exhibits signs of recent elevation and depression. A raised beach can be traced at heights of 90 feet above sea-level, and in other places submerged forests are found."

1 P. 79.

2 Nature, May 1902, vol. lxvi. p. 3.

WITH

CHAPTER VII

THE DEEPS OF THE OCEAN

WITH the increase of soundings the oceanic floor assumes an unsuspected variety in its form and configuration.

In studying the 'deeps,' which are concave depressions or troughs sinking down below the general floor-level of the basins in which they occur, this result of recent investigations must be kept steadily in view.

The forms or prominences rising above the general oceanic floor-level approximate to land forms, and lend colour to the view that the MidAtlantic was once an extensive and diversified land area.1

It seems indeed to be travelling out of the path of probability to assume that the Atlantic submerged ridges and the varying gradients of the Atlantic bottom are due to submarine volcanic action alone. No facts of geology lead us to draw such a tremendous inference. It will be shown before the completion of this chapter that the cubic content of these submerged ridges is

1 See 'Contributions to the Study of Volcanoes' (Judd) (Geo. Mag., 1876, p. 531).

enormous, and they are probably as enduring features of the globe as either oceans or continents. There is an ever-increasing mass of evidence pointing to a former greater elevation of the continents than what now exists.

Dr. Spencer has done much good pioneer work in this direction; and, though we may not be able to adopt his views to their full extent, he has certainly aroused the geological world to unsuspected possibilities. In connection with this question the discovery by the Deep-Sea Sounding Expedition already mentioned of the Libbey Deep, in lat. 40° N., long. 63° W., 3,318 fathoms; the Sigsbee Deep, in lat. 40° 11′ 51′′ N., long. 59° 51′ 30′′ W., 3,045 fathoms; and the Thoulet Deep, in lat. 40° 25′ 30′′ N., long. 58° 52′ W., 3,160 fathoms, is most interesting. These profound depths of the ocean exist within a distance of about a couple of hundred miles of the 100 fathoms platform on which Nova Scotia stands, the bordering continent being a very old land area long free from volcanic phenomena.

As facts accumulate we may expect these rigid views as to the unplastic character of the configuration of the sea floors to be rudely shaken.

Distinction between Sub-Oceanic and Land Forms. So far as we at present know, one of the main distinctions between the form of the ocean floor and that of the continental land is the existence in the oceans of great depressions, or 'deeps' as they are generally called.

Dana has treated of these, but necessarily in an incomplete manner. The method he adopts is largely that of inferences from analogical geographic forms, and the conclusions he comes to are mostly of a negative character.

In considering these continental and oceanic problems it is necessary to remember that the oceans occupy nearly three-fourths of the total area of the surface of the globe and the land but a little over one-fourth.2

The continents are thus protuberances rising through the waters. It follows as a geometrical truth that, the volume of the ocean waters remaining constant, the larger the area of land at any given period the deeper must have been the

oceans.

That is to say, the average depth must have been greater with every continental accretion and shallower with every continental reduction, always assuming that the surface area of the globe does not vary. If we look upon the continents as protuberances upon the spheroid and the oceans as depressions beneath it, we shall, in my opinion, take a correct view of their relations. If, further, the continental protuberances are due to increase of volume without variation of mass, as suggested in

1 •

On the Origin of the Deep Troughs of the Oceanic Depression: Are they of Volcanic Origin?' (Am. Jour. of Science, 1889, January to June, p. 192).

2 Herschel gives the dry land as 51 million square statute miles, and 146 million square miles as the extent of surface occupied by the ocean. 3 Some geologists maintain that the volume of water fluctuates.