The whole Ozark
uplift being rich in iron, the acidulated drainage waters coming into
contact dissolved and took it in solution, to re-deposit where and when
conditions should be favorable. These conditions were found in the basin
among the hills and along its outlet.
In the Popular Science Monthly of January 1897, a short article by J.T.
Donald, entitled "A Curious Canadian Iron Mine," describes the same
thing going on at the present time in Lac a la Tortue, a small body of
water in the center of a tract of swamp land, which produces the
vegetation necessary to supply the acid required for a base of
operation.
Of the manner of deposition he says: "The solution of iron in vegetable
acid (in which the iron is in what the chemist calls the form of a
protosalt) is oxidized by the action of the air on the surface of the
lake into a persalt, which is insoluble, and appears on the surface in
patches that display the peculiar iridescence characteristic of
petroleum floating on water. Indeed, not infrequently these films of
peroxide of iron are incorrectly attributed to petroleum. These films
become heavy by addition of new particles; they sink through the water,
and in this manner, in time, a large amount of iron ore is deposited on
the lake bottom. It must not be supposed that the ore is deposited as a
fine mud or sediment.
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