Before quitting this subject, let us remember that both snow and frost are of great utility to the husbandman. The latter, by expanding the humidity with which the hard clods are penetrated, crumbles them into powder, and renders stiff land porous, friable, and mellow. It also clears the soil from the plague of insect life, which, if it increased without so powerful a check, would probably prove a terrible injury to the crops. Moreover, it so hardens in winter the moist soft ground as to permit of the necessary field operations being carried on. Snow, as Dr Child remarks,[12] is even more useful. It covers up the tender plants with a thick mantle, which defends them against the attacks of excessive cold. "God giveth snow like wool," and for somewhat the same purposes as wool. The mantle which so closely wraps about the gaunt limbs of the winter-stricken earth neither allows the internal heat to escape nor the external cold to enter in. It has been found that the inner surface of the snow seldom falls much below 32° F., although the temperature of the external air may be many degrees under the freezing-point; and it is known that this amount of cold can be endured by the crops without injury, so long as their covering protects them from the raking influence of the wind. In climates where the winter's cold is longer and more intense than in England, the protective influence of snow is much more plainly shown. Where it lies long and deep, it opens out routes that were impracticable in summer on account of their ruggedness, and prepares a smooth path for the sledge, or for the "lumberer," over which the largest trunks of the forest may be carried with ease to the river or canal.