Cane Hills.—On the western border of the table-land region, and here forming a strip only a few miles wide along the edge of the Mississippi bottom, but from 70 to 450 feet above it, lies the remnant of what farther south constitutes a wide and important agricultural belt; the Bluff or Loess formation, locally known as “the Cane Hills.” The soil is largely composed of grains of sand and silt cemented by lime carbonate; it is therefore calcareous, and as on the Pontotoc ridge, described above, we find here the black walnut, the tulip tree, ash and others, elsewhere restricted to the alluvial “bottoms,” on the ridges themselves, from sixty to a hundred feet above the stream beds.
Mississippi Bottom.—At the western foot of this bluff there lies the great Mississippi Bottom, with its rich soils and varied forest growth. This also, however, subdivides into at least three distinct soil and vegetative zones, viz., the sandy “Frontlands,” which lie on the immediate banks of the great river and its main branches, and the heavy clayey “Back-land” areas, whose soils are partly the product of modern swamp deposits from backwaters, partly result from the disintegration of strongly calcareous clays constituting the lower part of the Bluff or Loess formation. A third natural subdivision is the “Dogwood ridge,” a narrow belt of slightly elevated land, mostly above ordinary overflows, which extends diagonally from the Mississippi river to the Yazoo bottom, and seems to be the continuation of “Crowleys ridge” in Arkansas. Each of these soil belts has its own characteristic forest growth, as indicated in the table below the map.
We have here along an east-and-west line of about 200 miles, eleven markedly distinct zones of vegetation, readily recognized as such by every farmer, and each underlaid by a distinct geological terrane. It does seem as though a close study of these and of the soils overlying them should lead to some definite results showing the physico-chemical causes of these differences.
Lime apparently a governing Factor.—The connection of some of these changes in vegetation with the calcareous nature of the corresponding formation has already been referred to. As regards four of the eleven divisions, this is obvious even to the casual observer, and is well known to the population, who speak of the “lime country” or belts being, as a matter of common knowledge, the best land; in full accord with what, in Kentucky and elsewhere, has passed into a popular maxim.[186]
Taking as a guide the trees and plants which characterize the obviously calcareous lands, our next step should be to verify, if possible, the fact that wherever these occur naturally, lime is abundant in the soil in comparison with those lands in which such vegetation does not occur naturally, or perhaps even fails to flourish when planted without special fertilization. This the writer has sought to do, first in connection with the survey work of the state of Mississippi, and subsequently in the wider field that has since come under his observation.
SOIL BELTS IN SOUTHERN MISSISSIPPI.
In Mississippi, the general conclusions derived from the observations made on the northern cross section, are corroborated many times over in other portions of the state. Aside from the cretaceous prairie region, there runs across the middle of the state a belt of varying width, of calcareous tertiary beds, which also give rise to more or less extensive tracts of “black prairie” lands, interspersed with non-calcareous, mostly sandy ridges, the lower slopes of which, influenced by the calcareous beds, bear an oak and hickory growth, while the higher portions have only pine, and usually remain uncultivated. Southward of this “central prairie” belt lies the long-leaf-pine forest area of the state, underlaid throughout by sandy, non-calcareous formations, with poor sandy soils, save here and there in patches, which can be at once recognized by the replacement of the long-leaved pine by a vigorous oak growth; as is also the case where the pine area abuts against the calcareous “Cane Hills” on the west. The bottom soils of this region are largely “sour,” and bear the gallberry (Prinos glaber), bay galls (Persea Carolina), ti-ti (Cliftonia monophylla), candleberry (Myrica cerifera), various whortle-berries, the pitcher plants (Sarracenia), yellow star grass (Aletris), sundews, Xyris, Eriocaulon, and other plants of similar habits.
Vegetative and Soil Features of the Mississippi Coast Belt.—South of the long-leaf pine area lie the coast flats, with sour, sandy soils underlaid by stiff clays. On these “pine meadows” of the Mississippi coast occur some of the most striking cases of modifications of vegetation due to physical and chemical causes.
As is well known, the long-leaved pine habitually belongs to the dry sandy uplands of the Gulf States; the deciduous cypress, on the other hand, is most characteristic of the swamps, where its roots are permanently submerged in water. But on the pine meadows of the Mississippi coast we see these two incongruous trees growing side by side, though sadly worsted by their mutual concessions; their heights usually ranging from 12 to 15, rarely as much as 18 feet.[187] Yet both preserve their characteristic forms, the cypress being an exact miniature reproduction of the usual level-topped swamp form, except as to the “knee” feature; while the pine differs only in stature from its giant brethren of the pine hills, from which it can be traced down through all grades of transition. The soil on which this growth occurs is a sour, sandy one, one and a half to three feet in depth, underlaid by a solid, impervious gray clay, above which is usually found several inches of coffee-colored bottom water, which drains slowly into the sluggish water-courses, themselves carrying brownish, sour, but very clear waters. Analysis shows the soil to be sour and extremely poor, especially in its lime and phosphates ([see chapter 19, p. 352]); its herbaceous vegetation consists exclusively of very small-seeded, “calcifuge” plants (sedges, orchids, Juncus, Hæmodoraceæ, Xyris, Polygala, etc.). This land is wholly unproductive and affords but indifferent pasturage, except the first season after burning-over; probably because of the effect of the minute amount of ashes so added. As the coast is approached, the clay subsoil has an increasing depth of sandy soil-mass above it, and on these “sand hammocks” the long-leaved pine gradually assumes more and more of its usual stature; the cypress disappears, and the Cuban pine (here called pitch pine) gradually comes in; while the sedgy vegetation diminishes and finally disappears. On this land crops may be grown as in the long-leaf-pine uplands.
But on the immediate coast, evidently under the influence of the aboriginal “shell mounds,” the yellow sandy soil becomes blackish from the (humus-forming) effect of the lime thus supplied; and concurrently the coast live-oak (Q. virens), grape vines, the Hercules club (Aralia spinosa), “l’herbe a trois quarts” (Verbesina sp.), and numerous leguminous plants (which are wholly absent from the pine meadows) take possession of the land, which is very productive and has been specially utilized in the growing of Sea Island cotton. Here the clay stratum is 15 to 20 feet below the surface, and roots penetrate to great depths in the pervious soil, whose great thickness makes up for its low percentage of plant-food (see table below). This land is distinctly limited by the extent of the shell heaps, past or present, and shows a respectable percentage of lime.