For important observations on supposed changes of climate in our Western
prairie region, from cultivation of the soil and the introduction of
domestic cattle, see Bryant's valuable Forest Trees, 1871, chapter v.,
and Hayden, Preliminary Report on Survey of Wyoming, p. 455. Some
physicists believe that the waters of our earth are, from chemical of
other less known causes, diminishing by entering into new inorganic
combinations, and that this element will finally disappear from the
globe.]

In other cases, from injudicioua husbandry, or the diversion or choking
up of natural water-courses, it may become more highly charged with
humidity. An increase or diminution of the moisture of a soil almost
necessarily supposes an elevation or a depression of its winter or its
summer heat, and of its extreme if not of its mean annual temperature,
though such elevation or depression may be so slight as not sensibly to
raise or lower the mercury in a thermometer exposed to the open air. Any
of these causes, more or less humidity, or more or less warmth of soil,
would affect the growth both of wild and of cultivated vegetation, and
consequently, without any appreciable change in atmospheric temperature,
precipitation, or evaporation, plants of a particular species might
cease to be advantageously cultivated where they had once been easily
reared. [Footnote: The soil of newly subdued countries is generally
highly favorable to the growth of the fruits of the garden and the
orchard, but usually becomes much less so in a very few years. Plums, of
many varieties, were formerly grown, in great perfection and abundance,
in many parts of New England where at present they can scarcely be
reared at all; and the peach, which, a generation or two ago, succeeded
admirably in the southern portion of the same States, has almost ceased
to be cultivated there. The disappearance of these fruits is partly due