CONCLUSIONS ON ANCIENT CLIMATES. 21 
sion or choking up of natural water-courses, it may become 
more highly charged with humidity. An increase or diminu- 
tion 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.* 
prairie region, from cultivation of the soil and the introduction of domestic 
cattle, see BRYANT’S valuable Horest T’rees, 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 or 
other less known causes, diminishing by entering into new inorganic combina. 
tions, and that this element will finally disappear from the globe. 
* The soil of newly subdued countries is genera'ly highly favorable to the 
erowth 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 to the ravages of insects, which have in later years 
attacked them; but this is evidently by no means the sole, or even the prin- 
cipal cause of their decay. In these cases, it is not to the exhaustion of the 
particular acres on which the fruit trees have grown that we are to ascribe 
their degeneracy, but to a general change in the condition of the soil or the 
air; for it is equally impossible to rear them successfully on absolutely new 
land in the neighborhood of grounds where, not long since, they bore the 
finest fruit. 
I remember being told, many years ago, by intelligent early settlers of the 
State of Ohio, that the apple trees raised there from seed sown soon after the 
land was cleared, bore fruit in less than half the time required to bring to 
bearing those reared from seed sown when the ground had been twenty years 
under cultivation, 
