Ocean Forms - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 43

essay in perplexity. The depths of ocean, he said, were 'unknown to
us', noting that in some places sounding lines more than 6 kilometres
long had failed to reach the sea floor.
Humboldt wondered, too, at the way the coastlines of South
America and Africa seemed to match up, although he did not so
much look forward in this to ideas of continental drift and plate tec-
tonics, as seem to glance backwards a generation to the ideas of the
Comte de Buffon (see Chapter 9), who had contemplated the world in
pre-revolutionary France. Buffon had thought that the pointed shape
of South America was due to the flood of the Earth's primordial
waters, which condensed and fell as rain at the poles (falling there
because those regions cooled more rapidly than did the tropics) then
rushed towards the equator, scouring the landscape as they went.
Humboldt thought that the Atlantic Ocean resembled a meandering
valley, directing the flow of the eddying waters first to the west, then
to the east. 37
Humboldt saw from geological strata that the positions of land and
sea could change place, and was aware that the Earth's crust could rise
and fall. That did not mean that continent and ocean were completely
interchangeable. He thought the continents owed much of their bulk
to the 'eruption of quartzose porphyry', 38 thus considering continents
essentially as large volcanic masses rooted to the sea floor.
Humboldt's perplexity concerning the fundamental structure of
the planet can be forgiven. For how could one study that two-thirds
of the planet covered by water when that water, in bulk, was as opaque
as, and more impenetrable than, rock? At least miners could dig down
through rock, while no one, then, could swim to more than a few
metres below the surface of any mass of water. One could take sound-
ings from ships, but that was easier said than done. On a ship in the
nineteenth century that involved the reeling out of a rope (later designs
used string twine, then woven piano wire) with a weight or bucket (to