NOVEMBER 24, 1899. ] 
tion of the floor of the ocean, and I will 
thereafter indicate what appears to me to 
be the bearing of some of these results on 
speculations as to the evolution of the ex- 
isting surface features of our planet. 
Depth of the Ocean. 
Ail measurements of depth, by which we 
ascertain the relief of that part of the 
earth’s crust covered by water, are referred 
to the sea-surface; the measurements of 
height on the land are likewise referred to 
sea-level. It is admitted that the ocean 
has a very complicated undulating surface, 
in consequence of the attraction which the 
heterogeneous and elevated portions of the 
lithosphere exercise on the liquid hydro- 
sphere. 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 sound- 
ings 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 ten thousand 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 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 con- 
SCIENCE. 
753 
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 usu- 
ally 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 pub- 
lished in 1895. Again, the recent sound- 
ings of the German s.s. Valdivia in the At- 
lantic, 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 fath- 
oms were obtained in a region where the 
contour-lines indicated between 1,000 and 
2,000 fathoms. This latter discovery sug- 
gests 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 Ant- 
arctic 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 tendency of recent soundings is 
to extend the area with depths greater than 
1,000 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. 
The areas marked out by the contour- 
lines of depth are now estimated as follows: 
