The results 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 I,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 wagon 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 downhill for about 200 miles, to the point at which the bottom is now covered by I,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, tho 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 grayish-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 Globigerinae imbedded 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.