290 THE POPULAR SCIENCE MONTHLY. 



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 " be- 

 came 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 in- 

 creasing in size with the increase of the fire, for the heat from the burn- 

 ing 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 excel- 

 lent 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 fur- 

 nish 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 pre- 

 vent floods after heavy rains by holding back the water, and preventing 

 scarcity of water during droughts by gradually releasing the water gath- 

 ered 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 



