522 
were published the last two of the fifty volumes of Reports con- 
taining the scientific results of the voyage of H.M.S. Chal/enger. 
In that very able and detailed review there is no reference 
whatever to the work of the numerous expeditions which had 
been fitted out by this and other countries for the exploration of 
the depths of the sea, nor is there any mention of the great 
advance in our knowledge of the ocean during the period of 
sixty-five years then under consideration. This omission may 
be accounted for by the fact that, at the time of the formation 
of the British Association, knowledge concerning the ocean 
was, literally speaking, superficial. The study of marine 
phenomena had hitherto been almost entirely limited to the 
‘surface and shallow waters of the ocean, to the survey of coasts 
and of oceanic routes directly useful for commercial purposes. 
Down to that time there had been no systematic attempts to 
ascertain the physical and biological conditions of those regions 
of the earth’s surface covered by the deeper waters of the ocean ; 
indeed, most of the apparatus necessary for such investigations 
had not yet been invented. 
The difficulties connected with the exploration of the greater 
depths of the sea arise principally from the fact that, in the 
majority of cases, the observations are necessarily indirect. At 
the surface of the ocean direct observation is possible, but our 
knowledge of the conditions prevailing in deep water, and of all 
that is there taking place, is almost wholly dependent on the 
correct working of instruments, the action of which at the 
critical moment is hidden from sight. 
It was the desire to establish telegraphic communication 
between Europe and America that gave the first direct impulse 
to the scientific exploration of the great ocean-basins, and at the 
present day the survey of new cable routes still yields each year 
a large amount of accurate knowledge regarding the floor of the 
ocean. Immediately before the Challenger Expedition there 
was a marked improvement in all the apparatus used in marine 
investigations, and thus during the Challenger Expedition the 
great ocean-basins were for the first time systematically and 
successfully explored, This expedition, which lasted for nearly 
four years, was successful beyond the expectations of its pro- 
moters, and opened out a new era in the study of oceanography. 
A great many sciences were enriched by a grand accumulation 
of new facts. Large collections were sent and brought home, 
and were subsequently described by specialists belonging to 
almost every civilised nation. Since the Challenger Expedition 
there has been almost a revolution in the methods employed in 
deep-sea observations. The most profound abysses of the ocean 
are now being everywhere examined by sailors and scientific 
men with increasing precision, rapidity and success. 
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 ex- 
tent of those changes which the crust of the earth is now under- 
going and has undergone in past geological times. Our 
knowledge of the ocean is still very incomplete. So much has, 
however, already been acquired that the historian will, in all 
probability, point to the oceanographical discoveries during the 
past forty years as the most important addition to the natural 
knowledge of our planet since the great geographical voyages 
associated with the names of Columbus, Da Gama, and Magellan, 
at the end of the fifteenth and the beginning of the sixteenth 
centuries. 
It is not my intention on this occasion to attempt anyth ng 
like a general review of the present state of oceanographic 
science. But, as nearly all the samples of marine deposits col- 
lected during the past thirty years have passed. through my 
hands, I shall endeavour briefly to point out what, in general, 
their detailed examination teaches with respect to the present 
condition 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 existing surface 
features of our planet. 
Depth of the Ocean, 
All 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 
NO. 1561, VOL. 60] 
NATURE 
[SEPTEMBER 28, 1899 
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 1000 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 ac- 
cumulated 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 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 confidence 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 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. Again, the recent soundings of the German s.s. Valdivia 
in the Atlantic, Indian, and Southern Oceans have not caused 
very great alteration in the positions 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 
1000 and 2000 fathoms. 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. 
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 ap- 
proximation 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 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. 
The areas marked out by the contour-lines of depth are now 
estimated as follows :— 
Fms. Sq. geo. m. Per cent. 
Between the shore and 100 7,000,000 ... (or 7 of the sea-bed) 
5 100 ,, 1000 10,000,000 (or 10 ,, oA ) 
SS 1000 .,, 2000 22,000,000 (or 2t ,, nr ) 
a 2000 ,, 3000 57,000,000 (or 55 55 cf ) 
Over 3000 fathoms 7,000,000 ... (Or 7 55 > ) 
103,000,000 100 
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. It is interesting to note that the area 
within the 1o0o-fathom line occupies 7,000,000 square geo- 
graphical miles, whereas the area occupied by the next succeed- 
ing 900 fathoms (viz. between 100 and 1000 fathoms) occupies 
only 10,000,000 square geographical miles. This points to a 
relatively rapid descent of the sea-floor along the continental 
slopes between 100 and 1000 fathoms, and therefore confirms 
the results gained by actual soundings in this region, many of 
which indicate steep inclines or even perpendicular cliffs. 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. Again, the relatively large area covered 
by the continental shelf between the shore-line ‘and too fathoms 
points to the wearing away of the land by current and wave 
action. 
On the Chad/enger charts all areas where the depth exceeds 
