DEPTH OF THE OCEAN, 7 
Dr. Maury has constructed his fine oregraphic map of the basin of 
the Atlantic. Dr. Maury has also published many charts, giving the 
depths of the ocean, the substance of which is given in the accom- 
panying map, which represents the configuration of the Atlantic up 
to the tenth degree of south latitude, not in figures, as in Dr. Maury’s 
charts, but in tints ; diagonal lines from right to left, representing the 
shores of both hemispheres, indicate a depth of less than 1,000 
fathoms ; from left to right indicate bottom at 1,000 to 2,000 ; hori- 
zontal lines, 2,000 to 3,000 fathoms ; cross lines show an average 
depth of 3,000 to 4,000 fathoms ; finally, the perpendicular lines in- 
dicate a depth of. 4,000 fathoms and upwards. Solid black indicates 
continents and islands ; waving lines, surrounding both continents at 
a short distance from the shore, indicate the sands which surround 
the coast line at a little distance from the shore. 
The question may be asked, what useful purpose is served by 
taking soundings at great depths? To this we may quote the 
answer of Franklin to a question of similar tendency, addressed to 
aéronauts—‘‘ What purpose is served by the birth of a child?” 
Every fact in physics is interesting in itself; it forms a rallying point, 
round which, sooner or later, others will meet, in order to. establish 
some useful truth ; and the importance of making and - recording 
deep-sea soundings is established by the successful immersion of the 
transatlantic telegraph. 
At the bottom of the Atlantic there exists a remarkable plateau, 
extending from Cape Race in Newfoundland, to Cape Clear in 
Ireland, a distance of over 2,000 miles, with a breadth of 470 miles ; 
its mean depth along the whole route is estimated at two miles and a 
half, It is upon this telegraphic plateau, as it has been called, that 
the attempt was made to lay down the cable in 1858, and it is 
on it that the enterprise was so successfully completed during the 
year 1866. The surface of the plateau had been previously explored 
by means of Brooke’s apparatus, and the bottom was found to be 
composed chiefly of microscopic calcareous shells (Foraminifera), 
and a few siliceous shells (Diatomaceg). These delicate and fragile 
shells, which seemed to strew the bottom of the sea in beds of great 
thickness, were brought up by the sounding-rod in a state of perfect 
preservation, which proves that the water is remarkably quiet in 
these depths—an inference which is fully borne out by the condition 
in which the cable of 1858 was found, when picked up in 1866. 
The first exploration of this plateau was undertaken by the 
American brig Dolphin, which took 100 soundings 100 miles from 
