Illustrations of the Huttonian Theory of the EarthPlayfair, John
Science
Illustrations of the Huttonian Theory of the Earth
Playfair, John
Geology; Hutton, James, 1726-1797. Theory of the earth
Also, whatever be the irregularities of density, the tendency to a
change of figure will not cease till the body is moulded into that
particular spheroid which admits of being covered with water every
where to the same depth.[232] Thus it appears, that a solid of an
irregular figure, and of irregular density, provided it be in part
covered with water; and be at the same time subject to waste above the
surface of the sea, and reconsolidation under it, has a tendency to
acquire, in time, the same figure that it would have acquired had it
been entirely fluid.
[Footnote 232: In the same manner as a transition is thus made from an
irregular figure to a spheroid of equilibrium, so, if the actual figure
were at first more simple than the spheroid, it would still be changed
into this last by degrees.
Let us conceive, for instance, that the earth is at rest, and is a
perfect sphere of solid matter, surrounded by an ocean every where of
equal depth, for example, of one mile. Then, if a rotatory motion be
communicated to it, so that it shall revolve on its axis in twenty-four
hours, in consequence of the centrifugal force, the water circumfused
about the sphere will immediately rise up under the equator, and will
become part of a spheroidal surface, (not elliptical, but nearly so,)
the equatorial diameter of which is greater than the polar axis, in the
ratio of 588 to 577 By this means the water will be accumulated at the
equator to the depth of nearly 2.5 miles, and form a zone surrounding
the earth, and extending about 37° on each side of the equator. The
remainder of the surface will be left dry, forming two vast circumpolar
continents, that reach 53° on every side of the poles, and that are
elevated in the middle more than four miles above the level of the sea.
Such would be the state of our globe, on the hypothesis above laid
down; and, if there were no waste or destruction of the land, this
order of things would be permanent, and neither the solid nor fluid
part of the mass could ever acquire any other figure than that which
has been described. But, if the same laws be supposed to regulate the
action of the atmosphere in those circumstances, that do actually
regulate it according to the present constitution of the globe, the
vapours raised up from the surface of the sea, would be carried by the
winds over the land, where they would be condensed and precipitated in
rain. Thus, all the agents of destruction would be let loose on the two
great circumpolar continents; rivers would be formed; the land would
become deeply intersected by ravines; those ravines would gradually
open into wide valleys; the masses of greatest resistance would be
shaped into hills and mountains: and from a superficies originally
smooth and uniform, the same inequalities would be produced which at
present diversify the surface of the earth.
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