Measured Gowing's Swamp two and a half rods northeast of the middle of the hole, i. e. in the andromeda and sphagnum near its edge, where I stand in the summer; also five rods northeast of the middle of the open hole, or in the midst of the andromeda.
In both these places the pole went hard at first, but broke through a crust of roots and sphagnum at about three feet beneath the surface, and I then easily pushed the pole down just twenty feet. This being a small pole, I could not push it any further holding it by the small end; it bent then. With a longer and stiffer pole I could probably have fathomed thirty feet.
It seems, then, that there is, over this andromeda swamp, a crust about three feet thick, of sphagnum, andromeda (calyculata and Polifolia), and Kalmia glauca, etc., beneath which there is almost clear water, and, under that, an exceedingly thin mud.
There can be no soil above that mud, and yet there were three or four larch trees three feet high or more between these holes, or over exactly the same water, and there were small spruces near by. For aught that appears, the swamp is as deep under the andromeda as in the middle.
The two andromedas and the Kalmia glauca may be more truly said to grow in water than in soil there. When the surface of a swamp shakes for a rod around you, you may conclude that it is a network of roots two or three feet thick resting on water or a very thin mud. The surface of that swamp, composed in great part of sphagnum, is really floating.
It evidently begins with sphagnum, which floats on the surface of clear water, and, accumulating, at length affords a basis for that large-seeded sedge (?), andromedas, etc. The filling up of a swamp, then, in this case at least, is not the result of a deposition of vegetable matter washed into it, settling to the bottom and leaving the surface clear, so filling it up from the bottom to the top; but the vegetation first extends itself over it as a film, which gradually thickens till it supports shrubs and completely conceals the water, and the under part of this crust drops to the bottom, so that it is filled up first at the top and the bottom, and the middle part is the last to be reclaimed from the water.
Perhaps this swamp is in the process of becoming peat.
This swamp has been partially drained by a ditch.
I fathomed also two rods within the edge of the blue berry bushes, in the path, but I could not force a pole down more than eight feet five inches; so it is much more solid there, and the blueberry bushes require a firmer soil than the water andromeda.
This is a regular quag, or shaking surface, and in this way, evidently, floating islands are formed. I am not sure but that meadow, with all its bushes in it, would float a man-of-war.
H. D. Thoreau, Journal, February 1, 1858
There is a crust about three feet thick of sphagnum, andromeda and Kalmia glauca, beneath which there is almost clear water. See January 30, 1858 ("To my surprise, I found clear water under this crust of sphagnum"); August 23, 1854 ("There is . . .an abrupt edge next the water, this on a dense bed of quaking sphagnum, in which I sink eighteen inches in water, upheld by its matted roots, where I fear to break through”).
This swamp has been partially drained by a ditch. See November 23, 1857 ("This swamp appears not to have had any natural outlet, though an artificial one has been dug. The same is perhaps the case with the C. Miles Swamp. And is it so with Beck Stow's These three are the only places where I have found the Andromeda Polifolia. The Kalmia glauca in Gowing's, C. Miles's, and Holden's swamps. The latter has no outlet of any kind.")
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