Page:Popular Science Monthly Volume 23.djvu/536

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of coniferous trees; while some of the trees peculiar to the valleys west of the Alleghanies grow on the Silurian and Devonian beds.

The Appalachian province is composed of all the geological formations of North America, and its regions are very distinct.

The Alleghany region, comprising the eastern slopes of the uplands, and the lower Alleghanies, terminating in a point of latitude 34° in Georgia, is mostly granitic, but has streaks of Silurian and Triassic running through it. We find the same class of trees in it that grow in the Canadian region (Canada), with a few added which are perhaps limited by heat. These, with a few oaks and hickories, which are more prevalent on the Triassic formation than elsewhere, form the bulk of the forest-growth.

The Ohio region, embracing the eastern uplands of the Ohio Valley, east of the prairies and north of latitude 38°, is composed geologically almost wholly of Silurian, Devonian, and carboniferous beds, covered in places with drift from the north. It is marked by its large number of deciduous trees, no other country boasting of so many fine oaks, hickories, and walnuts. It is, however, very poor in coniferæ, and, but for a few stragglers, might be said to have none. Allied species are found to be plentiful in the tertiary formation nearly across the continent, indicating that this class of trees at one time reached from the Alleghanies to the Rocky Mountains, the middle of the belt having been destroyed by the more recent changes of the physical conditions of the earth's surface. As they have never returned since the glacial epoch, the inference is that the conditions of soil and climate have been so changed that the country west of the ninety-seventh degree of longitude is not capable of supporting these trees.

The Tennesseean region is a southwestern continuation of the Ohio region. It is composed of the same geological beds, with a few spurs of the granite ridges of the Alleghanies running into it, and therefore contains more coniferæ than the Ohio region. Still, the bulk of its timber is of the same class of broad-leaved trees that are found north of it, the only differences being such as climate alone makes.

The Carolinian region borders on the Atlantic coast between the Alleghany Mountains and the ocean from Middle Georgia to Long Island. It is composed of cretaceous and tertiary beds, with a strip of Triassic along the western edge. In the northern portion are some beds of drift of granite from the north. Here we have a distinct class of coniferæ on the cretaceous beds that are peculiar to this region, and another class on the drift that are also found growing farther north. Arthur Hollick,[1] who has made observations on the flora of Staten Island, says: "We have on Staten Island two well-marked geological formations: the drift, which covers about two thirds of the entire island, nearly all of the northern part, and extending as far

  1. "Bulletin of the Torrey Botanical Club," vol. vii, p. 14.