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 200 miles
to the point at which the bottom is now covered by 1700 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, greyish 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.
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