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 of Atlantic mud which he procured were sent to me to be examined and reported upon.

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 seventeen hundred 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 wagon all the way from Valentia, on the west coast of Ireland, to Trinity Bay in Newfoundland.  And, except upon one sharp incline about two hundred 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 two hundred miles to the point at which the bottom is now covered by seventeen hundred 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 ten thousand to fifteen thousand 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 three hundred 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 grayish white friable substance.  You can write with this on a black-board, 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 Globigerinae 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 nature of the Globigerinae of the chalk—­it is unnecessary to speak of them.