[87] J. D. Baldwin’s Ancient America, p. 47.
[88] Foster, pp. 172–3, remarks: “Squier and Davis hastily stated that none of these works occupied the alluvial bottoms (an error which Mr. Squier subsequently corrected), and from this statement the most erroneous conclusions as to their antiquity have been drawn. There is nothing to indicate but that those works were constructed after the surface had assumed its present configuration, and that the climate had become essentially as it is now. That they should not occur as abundantly on the bottoms as on the river terraces is not to be wondered at, when we consider the great fluctuations of the Mississippi and its tributaries. The extreme range between low and high water of the Upper Mississippi at its mouth is thirty-five feet; that of the Missouri at its mouth about the same; and that of the Ohio at Louisville, forty-two feet. Hence, during the flood time a greater portion of the bottom lands are subject to overflow, and it would be natural for the Mound-builders to shun such situations. Where the immediate valleys lie above high water, we find their works. Of this the ‘American Bottom’ is a notable instance.”
[89] See Dr. Lapham’s communication in Foster’s Pre-Historic Races, pp. 373–5, in which he shows the possibility of finding the average increase of wood each year by measuring annual rings of growth.
[90] Sir Charles Lyell, Antiquity of Man, p. 41, says: “When I visited Marietta in 1842, Dr. Hildreth took me to one of the mounds, and showed me where he had seen a tree growing on it, the trunk of which when cut down displayed eight hundred rings of annual growth.”
[91] See Prof. Asa Gray in Foster’s Pre-Historic Races, p. 392; also Lyell’s Antiquity of Man, p. 41, where the opinion of President Harrison is quoted as follows: “We may be sure that no trees were allowed to grow so long as the earthworks were in use; and when they were forsaken, the ground, like all newly-cleared land in Ohio, would for a time be monopolized by one or two species of tree, such as the yellow locust and the black or white walnut. When the individuals which were the first to get possession of the ground had died out one after the other, they would, in many cases, instead of being replaced by other species, be succeeded, by virtue of the law which makes a rotation of crops profitable in agriculture, by other kinds, till at last, after a great number of centuries (several hundred years perhaps), that remarkable diversity of species characteristic of North America, and far exceeding what is seen in European forests, would be established.”
[92] Foster’s Pre-Historic Races, pp. 118, 119, 122, and M. Stronck, Repères chronologiques de l’histoire des Mound-builders in Congrès des Américanistes, Luxembourg, tom. i, pp. 316–18, catalogues the record of the age of trees found on mounds.
[93] Foster’s Pre-Historic Races, p. 370.
[94] American Naturalist, Jan. 1868.
[95] Second Visit to the United States, vol. i, p. 252.
[96] Dr. Brinton’s Notes on the Floridian Peninsula.