148 
DEAD PRODUCTS OF TREES—SOIL OF FOREST. 
canopy between the ground and the shy, and materially inter¬ 
fere with both processes. 
d. Dead Products of Trees. 
Besides this various action of standing trees considered as 
inorganic matter, the forest exercises, by the annual moulting 
of its foliage, still another influence on the temperature of the 
earth, and, consequently, of the atmosphere which rests upon 
it. If you examine the constitution of the superficial soil in a 
primitive or an old and undisturbed artificially planted wood, 
you find, first, a deposit of undecayed leaves, twigs, and seeds, 
lying in loose layers on the surface ; then, more compact beds 
of the same materials in incipient, and, as you descend, more 
and more advanced stages of decomposition ; then, a mass of 
black mould, in which traces of organic structure are hardly 
discoverable except by microscopic examination; then, a 
stratum of mineral soil, more or less mixed with vegetable 
matter carried down into it by water, or resulting from the 
decay of roots ; and, finally, the inorganic earth or rock itself. 
Without this deposit of the dead products of trees, this latter 
would be the superficial stratum, and as its powers of absorp¬ 
tion, radiation, and conduction of heat would differ essentially 
from those of the layers with which it has been covered by the 
droppings of the forest, it would act upon the temperature of 
the atmosphere, and be acted on by it, in a very different way 
from the leaves and mould which rest upon it. Leaves, still 
entire, or partially decayed, are very indifferent conductors of 
heat, and, therefore, though they diminish the warming influ¬ 
ence of the summer sun on the soil below them, they, on the 
other hand, prevent the escape of heat from that soil in win¬ 
ter, and, consequently, in cold climates, even when the ground 
is not covered by a protecting mantle of snow, the earth does 
not freeze to as great a depth in the wood as in the open field. 
