them up "within the limits of vegetation."

As early as 1807, Judge Peters, of Philadelphia, became satisfied that all
that elevated region around the head waters of the Delaware, Alleghany,
and Genesee Rivers, then covered with heavy growths of hemlock, or with
forests of beech and sugar-maple, was originally an oak forest, probably
covering most of that entire region. And Mr. John Adlum, of Havre de
Grace, Md., who originally surveyed the lands south of the great bend of
the Susquehanna, between that river and the Delaware, conceived the same
idea as early as 1788. The section surveyed by him was chiefly covered
with beech and sugar-maple; in fact, it was in what was called, at the
time, "the beech and sugar-maple country." He drew his inferences from the
fact that he found, here and there, at irregular intervals, red and white
oaks growing to an enormous size, none being less than sixteen feet, and
many measuring twenty-two feet or more, in circumference five feet above
the ground. He says that "the hemlock in this region seems to have
succeeded the oak, while the beech and maple no doubt succeeded the
hemlock." This last inference would seem to have been made from the fact
that clumps of large hemlock trees were, at that time, still growing at
intervals among the larger deciduous trees.

Indeed, there is no better established fact in vegetable physiology than
that of these alternations of forest growths. They sometimes come on
gradually, but, in a majority of instances, they make their appearance at
once on the cutting off of old forests, in the tracks of tornadoes, or
where fire has devastated extensive regions of timber. From the facts
which have been gathered, it is difficult to determine any regular order
of alternation, except that oaks and other deciduous trees succeed the
different varieties of pine and other evergreen growths, and, perhaps,
_vice versa_. In Dr. Hough's report upon American Forestry, he makes a