GEOGRAPHICAL CHANGE. ok 
half-civilized regions, too, windfalls are more frequent than in 
those where the forest is unbroken, because, when openings have 
been made in it for agricultural or other purposes, the entrance 
thus afforded to the wind occasions the sudden overthrow of 
hundreds of trees which might otherwise have stood for gene- 
rations and have fallen to the ground, only one by one, as natu- 
ral decay brought them down.* Besides this, the flocks bred 
by man in the pastoral state keep down the incipient growth of 
trees on the half-dried bogs, and prevent them from recovering 
their primitive condition. 
Young trees in the native forest are sometimes girdled and 
killed by the smaller rodent quadrupeds, and their growth is 
checked by birds which feed on the terminal bud; but these 
animals, as we shall see, are generally found on the skirts of 
the wood only, not in its deeper recesses, and hence the mis- 
chief they do is not extensive. 
In fine, in countries untrodden by man, the proportions and 
relative positions of land and water, the atmospheric precipita- 
tion and evaporation, the thermometric mean, and the distribu- 
tion of vegetable and animal life, are maintained by natural 
compensations, in a state of approximate equilibrium, and are 
ubject to appreciable change only from geological influences 
so slow in their operation that the geographical conditions may 
be regarded as substantially constant and immutable. 
Natural Conditions favorable to Geographical Change. 
There are, nevertheless, certain climatic conditions and cer- 
tain forms and formations of terrestrial surface, which tend 
respectively to impede and to facilitate the physical degrada- 
* Careful examination of the peat mosses in North Sjalland—which are so 
abundant in fossil wood that, within thirty years, they have yielded above a 
million of trees—shows that the trees have generally fallen from age and not 
from wind. They are found in depressions on the declivities of which they 
grew, and they lie with the top lowest, always falling towards the bottom 
of the valley.—VAUPELL, Bégens Indvandring i de Danske Skove, pp. 10, 14. 
