754 
Between the shore and 100 fms., 
SCIENCE. 
[N. S. Von. X. No. 256. 
7,000,000 sq. geo. m. (or 7% of the sea-bed) 
8G 100 ‘* 1,000 ‘ 10,000,000 “ <‘ (or10% * Gore h 
G6 1,000 ‘* 2,000 ‘‘ 22,000,000 “* ‘ (or2l% Bo 
a 2,000 ‘ 3,000 “ 57,000,000 “ <“ (or55% “ GBF 59)) 
Over 3,000 fathoms, 7,000,000 ‘‘ se (or 7% ‘ ns ) 
103,000,000 sq. geo. m. 100 ~— percent. | 
From these results it appears that con- 
siderably more than half of the sea-floor 
lies at a depth exceeding 2,000 fathoms, or 
over two geographical miles. It is inter- 
esting to note that the area within the 100- 
fathom line occupies 7,000,000 square geo- 
graphical miles, whereas the area occupied 
by the next succeeding 900 fathoms (viz., 
between 100 and 1,000 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 1,000 fathoms, and, there- 
fore, 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 con- 
tinental 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 3,000 fathoms have been 
called ‘ Deeps,’ and distinctive names have 
been conferred upon them. Forty-three 
such depressions are now known, and the 
positions of these are shown on the map 
here exhibited ; twenty-four are situated in 
the Pacific Ocean, three in the Indian 
Ocean, fifteen in the Atlantic Ocean and 
one in the Southern and Antarctic Oceans. 
The area occupied by these thirty-nine 
deeps is estimated at 7,152,000 square geo- 
graphical miles, or about 7 per cent. of the 
total water-surface of the globe. Within 
these deeps over 250 soundings have been 
recorded, of which twenty-four exceed 
4,000 fathoms, including three exceeding 
5,000 fathoms. 
Depths exceeding 4,000 fathoms (or four 
geographical miles) have been recorded 
within eight of the deeps, viz., in the North 
Atlantic within the Nares Deep; in the 
Antarctic within the Ross Deep; in the 
Banda Sea within the Weber Deep ; in the 
North Pacific within the Challenger, Tus- 
carora and Supau Deeps, and in the South 
Pacific within the Aldrich and Richards 
Deeps. Depths exceeding 5,000 fathoms 
have been hitherto recorded only within 
the Aldrich Deep of the South Pacific, to 
the east of the Kermadecs and Friendly 
Islands, where the greatest depth is 5,155 
fathoms, or 530 feet more than five geo- 
graphical miles, being about 2,000 feet more 
below the level of the sea than the summit 
of Mount Everest in the Himalayas is above 
it. The levels on the surface of the litho- 
sphere thus oscillate between the limits of 
about ten geographical miles (more than 
eighteen kilometers). 
Temperature of the Ocean-Floor. 
Our knowledge of the temperature on 
the floor of the ocean is derived from 
observations in the layers of water immedi- 
ately above the bottom by means of deep- 
sea thermometers, from the electric resist- 
ance of telegraph cables resting on the bed 
of the great ocean-basins, and from the 
temperature of large masses of mud and 
ooze brought up by the dredge from great 
. 
