Page:Popular Science Monthly Volume 13.djvu/304

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and soil, as far down as I could conveniently dig with my hands, with a thermometer, and found a temperature of from 37° to 40° Fahr. I afterward dug down, in several places, through the "duff," and in each place found ice or frozen ground.

After this, it was perfectly clear to my mind that this "duff" became thoroughly saturated with water during the fall rains, and that it was frozen to the bottom during the long, severe winters of this climate. It is not an uncommon thing for the ground in the valleys, hundreds of feet below the level of these kilns, to freeze to the depth of four feet during the winter.

The "duff" being frozen at the bottom accounts for the brook increasing in size with the increase of the fire, for the heat from the burning of the top "duff" would cause the ice to melt, and the water would find its way into the brook. This "duff," like all woody substances, is a poor conductor of heat, and when once frozen and protected, as it is in its natural state by the shade of the timber, would thaw out very slowly, and would continue to furnish a supply of water all summer; and very hot weather, causing low water in other places, would tend to increase the supply from this source.

During the latter part of the summer of 1877 I examined "duff" in several places, but did not find any ice; but found the "duff," in every instance, thoroughly saturated with water. It should be remembered that the summer of 1877 was unusually wet, and that water is an excellent conductor of heat, and that water from the rains, running over the ice, would melt it much sooner than it could be melted by what heat could be communicated from the sun, through its woody covering, in a dry season. At most, this would tend to show that the ice lasts only part of the summer, but, if that is a fact, the frozen "duff" would furnish a reservoir as long as the ice lasted, and, during the rest of the summer, would act as an absorbent, taking up and holding the showers, and gradually letting the water down into the streams, tending to prevent floods after heavy rains by holding back the water, and preventing scarcity of water during droughts by gradually releasing the water gathered from the storms.

In addition to the "duff," the sides of many of our mountains are covered with a heavy moss, which also acts as a sponge in the manner described above, in preventing floods and supplying water during dry seasons; and this moss, like the "duff," entirely disappears when the land is cleared, and, like the "duff," does not form again under the pines and deciduous trees that follow the spruce. The spruce-timber affords a dense shade, and, as long as the timber is left standing, this "duff" seldom gets dry enough to burn, but, when the timber is cut, the top of the "duff" dries, and is burned, as far down as it is dry enough to burn, by the forest-fires that are so common in this part of the country. This is repeated, year after year, until the "duff" is all burned off, and the sand and bowlders appear upon the surface; after