CONDITION OF THE FLOOR OF THE OCEAN. 311 



face. The measurements of height on the land are likewise referred to 

 sea level. It is admitted that the ocean has a very complicated undu- 

 lating surface in consequence of the attraction which the heteroge- 

 neous and elevated portions of the lithosphere exercise on the liquid 

 hydrosphere. In the opinion of geodesists the geoid .may in some 

 places depart from the figure of the spheroid by 1,000 feet. Still it 

 is not likely that this surface of the geoid departs so widely from the 

 mean ellipsoidal form as to introduce a great error into our estimates 

 of the elevations and depressions on the surface of the lithosphere. 



The soundings over the water surface of the globe have accumulated 

 at a rapid rate during the past fifty years. In the shallow water, 

 where it is necessary to know the depth for purposes of navigation, 

 the soundings may now be spoken of as innumerable. The 100-fathom 

 line surrounding the land can therefore often be drawn in with much 

 exactness. 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 10,000 deep soundings have been taken 

 by British ships alone. The deep soundings are scattered over the 

 different ocean basins in varying proportions, being now most numer- 

 ous in the North Atlantic and Southwest Pacific, and in these two 

 regions the contour lines of depth may be drawn in with greater con- 

 fidence than in the other divisions of the great ocean basins. 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 engi- 

 neers, have, from a general point of view, necessitated but little altera- 

 tion in the contour lines drawn on the Challenger bathymetrical maps, 

 published in 1895. Again, the recent soundings of the German steamship 

 Yaldivia in the Atlantic, Indian, and Southern oceans have not caused 

 very great alteration in the positions of the contour lines on the Chal- 

 lenger maps, if we except one occasion in the South Atlantic when a 

 depth of 2,000 fathoms was expected and the sounding machine 

 recorded a depth of only 536 fathoms, and again in the great Southern 

 Ocean, when depths exceeding 3,000 fathoms were obtained in a region 

 where the contour lines indicated between 1,000 and 2,000 fathoms. 

 This latter discovery suggests that the great depth recorded by Ross 

 to the southeast of South Georgia may not be very far from the truth. 



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. On the 

 whole, it may be said that the general teudenc}^ of recent soundings is 



