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 brief summary of the order of these alternations in different sections of the country, on the authority of persons apparently more or less well-informed on the subject, but by no means accurate observers. He says that in the region about Green Bay, Wis., overrun by the fires of 1871, "dense growths of poplars and birches have sprung up, and are growing rapidly;" but he omits the most important fact of all, in his failure to state the previous growths of timber, or whether there were any neighboring growths of poplar along the track of the burnt district from which seed might have been derived. Here are some of his more important statements:-- "At Clarksville, Ga., oak and hickory lands, when cleared, invariably grew up with pine. This is true of that region of country generally." "At Aiken, S.C., the long-leaf pine is succeeded by oaks and other deciduous trees, and _vice versa_." "In Bristol County, Mass., in some cases, after pines have been cut off, oak, maple, and birch have sprung up abundantly."