Discourses: Biological and Geological Essays | Page 6

nautical
purposes, scientific accuracy could not be expected from the armed
lead, and to remedy its defects (especially when applied to sounding in
great depths) Lieut. Brooke, of the American Navy, some years ago
invented a most ingenious machine, by which a considerable portion of
the superficial layer of the sea-bottom can be scooped out and brought
up from any depth to which the lead descends. In 1853, Lieut. Brooke
obtained mud from the bottom of the North Atlantic, between
Newfoundland and the Azores, at a depth of more than 10,000 feet, or
two miles, by the help of this sounding apparatus. The specimens were
sent for examination to Ehrenberg of Berlin, and to Bailey of West
Point, and those able microscopists found that this deep-sea mud was
almost entirely composed of the skeletons of living organisms--the
greater proportion of these being just like the Globigerinoe already
known to occur in the chalk.
Thus far, the work had been carried on simply in the interests of
science, but Lieut. Brooke's method of sounding acquired a high
commercial value, when the enterprise of laying down the
telegraph-cable between this country and the United States was
undertaken. For it became a matter of immense importance to know,

not only the depth of the sea over the whole line along which the cable
was to be laid, but the exact nature of the bottom, so as to guard against
chances of cutting or fraying the strands of that costly rope. The
Admiralty consequently ordered Captain Dayman, an old friend and
shipmate of mine, to ascertain the depth over the whole line of the
cable, and to bring back specimens of the bottom. In former days, such
a command as this might have sounded very much like one of the
impossible things which the young Prince in the Fairy Tales is ordered
to do before he can obtain the hand of the Princess. However, in the
months of June and July, 1857, my friend performed the task assigned
to him with great expedition and precision, without, so far as I know,
having met with any reward of that kind. The specimens or Atlantic
mud which he procured were sent to me to be examined and reported
upon.[1]
[Footnote 1: See Appendix to Captain Dayman's _Deep-sea Soundings
in the North Atlantic Ocean between Ireland and Newfoundland, made
in H.M.S. "Cyclops_." Published by order of the Lords Commissioners
of the Admiralty, 1858. They have since formed the subject of an
elaborate Memoir by Messrs. Parker and Jones, published in the
_Philosophical Transactions_ for 1865.]
The result of all these operations is, that we know the contours and the
nature of the surface-soil covered by the North Atlantic for a distance
of 1,700 miles from east to west, as well as we know that of any part of
the dry land. It is a prodigious plain--one of the widest and most even
plains in the world. If the sea were drained off, you might drive a
waggon all the way from Valentia, on the west coast of Ireland, to
Trinity Bay, in Newfoundland. And, except upon one sharp incline
about 200 miles from Valentia, I am not quite sure that it would even
be necessary to put the skid on, so gentle are the ascents and descents
upon that long route. From Valentia the road would lie down-hill for
about 200 miles to the point at which the bottom is now covered by
1,700 fathoms of sea-water. Then would come the central plain, more
than a thousand miles wide, the inequalities of the surface of which
would be hardly perceptible, though the depth of water upon it now
varies from 10,000 to 15,000 feet; and there are places in which Mont

Blanc might be sunk without showing its peak above water. Beyond
this, the ascent on the American side commences, and gradually leads,
for about 300 miles, to the Newfoundland shore.
Almost the whole of the bottom of this central plain (which extends for
many hundred miles in a north and south direction) is covered by a fine
mud, which, when brought to the surface, dries into a greyish white
friable substance. You can write with this on a blackboard, if you are so
inclined; and, to the eye, it is quite like very soft, grayish chalk.
Examined chemically, it proves to be composed almost wholly of
carbonate of lime; and if you make a section of it, in the same way as
that of the piece of chalk was made, and view it with the microscope, it
presents innumerable Globigerinoe embedded in a granular matrix.
Thus this deep- sea mud is substantially chalk. I say substantially,
because there are a good many minor differences; but as these have no
bearing on the question immediately before us,--which is the