APPENDIX.

PHYSICAL GEOGRAPHY AND NATURAL DIVISIONS OF ALABAMA.

BY EUGENE ALLEN SMITH, PH.D., PROFESSOR OF GEOLOGY, UNIVERSITY OF ALABAMA.

ALABAMA is situated between the eighty-fifth and eighty-ninth meridians of west longitude, and mainly between the thirty-first and thirty-fifth parallels of north latitude. The thirty-fifth parallel makes the northern boundary* of the State, and the thirty-first the southern, with the exception of that part west of the Perdido River, which extends south to the Gulf of Mexico. The total area thus included is, according to the latest estimates, 52,251 square miles, of which 51,540 constitute the land surface.

SURFACE CONFIGURATION AND GRAND DIVISIONS.-Leaving out of account the smaller inequalities, the surface of the State may be considered as an undulating plain, whose mean elevation above sea level cannot be much less than 600 feet. Towards the north and east the surface rises above this level, and towards the south and west it sinks below it. A curving line drawn from the northwestern corner of the State through Tuscaloosa and Montgomery to Columbus, Georgia, would mark approximately the lower boundary of the area whose altitude is above 600 feet. This elevated land is the terminus towards the southwest of the great Appalachian mountain system, and it may therefore fittingly be designated as the Appalachian area. The line along which the highest altitudes occur. i.e., the axis of elevation of this area, runs northeast nearly along the northern boundaries of Coosa, Clay, and Cleburne counties, the altitude increasing towards the northeast.

As a

* As a matter of fact, this parallel does not exactly coincide with the northern boundary.

consequence the general slope of the surface is away from this elevated region towards the northwest, west, southwest, south, and southeast. The mountains of the State all rise above this high land to elevations of 1,200 to 1,500 feet, or to 2,000 to 2,400 feet above sea level.

The rest of the State, whose general altitude is less than 600 feet, may be called the Coastal Plain. The surface of this Coastal Plain has a slope south and west towards the Gulf of Mexico and the Mississippi Valley. In elevation it declines from about 600 feet, where it touches the Appalachian division, to about 200 or 300 feet in the highlands overlooking the Gulf in the two coast counties. Into the materials of this gently sloping plain the rivers and other streams have sunk their channels, leaving between the remnants of the original mass which constitute the hills of this section of the State.

Another point of difference between these two great divisions, which an inspection of the map will impress upon the student, is the prevailing northeast and southwest direction of the minor subdivisions of the Appalachian area, and the approximately east and west trend of these divisions in the Coastal Plain area. These and other radical differences are due to the difference in the age and degree of consolidation of the component rock formations of the two divisions; to the different amounts of disturbance from their originally horizontal position which these strata have suffered; to the varying degree of adjustment of the drainage systems to the structure of the country, and to other causes, the discussion of which would be more appropriate to a geological than to a geographical description of the State. It is hoped, however, that some of the causes of these differences will be made plain in the course of what follows.

RIVER SYSTEMS.-In general terms, two things have been mainly instrumental in determining the direction of the drainage of Alabama. These are, first, the slopes toward the northwest and southeast away from the Appalachian axis of elevation above spoken of; and, second, the more general slope of the surface of the State, taken as a whole, southwestward towards the Mississippi Valley. An examination of the map will show that the latter cause has greatly outweighed the former in fixing the direction of the water courses, with the result of giving a general southwest direction to the whole drainage system of the State, with the single exception of that of the Tennessee River.

In the southeastern half of the Appalachian area, while the natural fall is southeast and south, most of the streams, and especially the minor ones, are also influenced by the northeast and southwest trend of the valleys and ridges, i.e., by the geological structure, and they make

PHYSICAL GEOGRAPHY.

iii

their way towards the Coastal Plain in a zig-zag course, alternating between south east and southwest. In the northwestern half of the Appalachian region, the two branches of the Warrior River follow in general the troughs or basins of the coal field of the same name, which decline towards the southwest; while the Tennessee, entering the State near its northeastern corner, follows a limestone valley southwestward to Guntersville, then turns northwestward down the slope from the axis of the Appalachian highlands.

In the central part of the Appalachian region the dependence of the minor ridges and valleys upon the geological structure is most clearly seen, for they all have a northeast-southwest trend, which is the trend of the outcropping edges of the inclined or sloping strata, the valleys being cut into the limestones and other more easily eroded rocks, while the harder rocks stand out in the ridges.

In the Coastal Plain region the main streams have southwesterly courses determined by the general slope of the surface, while their smaller tributaries, as well as the ridges and small valleys to which they have given rise, show a close dependence upon the character of the materials of the geological formations and upon their position or attitude. Throughout the Coastal Plain the constituent strata or beds of sand, clay, limestone, and marl have a slope or dip in the same general direction as that of the surface of the country, but at a more rapid rate, which is on an average about 35 feet to the mile. And while the main streams have cut across the edges of these slightly inclined beds, the smaller streams run roughly parallel to the same. The result is that the landward-facing slopes of the valleys of these minor streams are steep and abrupt, while the slopes facing gulfward are very gentle, often hardly to be distinguished from horizontal. Thus, while the adjustment of the smaller streams of the Coastal Plain to the geological structure is not as striking, it is in places quite as complete as in the Appalachian region.

MOUNTAINS AND TABLE-LANDS.-As has been intimated above, the mountainous region of the State is confined to the Appalachian division. In the southeastern half of this division, the component strata of the mountains have been much folded and plicated, and the mountains are, as a rule, sharp-crested and serrated, while in the northwestern half the strata are in wide, open waves or folds, and the mountains are merely the remnants of an elevated table-land, the Cumberland Plateau, with steep sides and flat tops. In the Coastal Plain there are no mountains, properly speaking; and the hills, like the spurs of the Cumberlands, are simply the parts of the general mass of the country left more or less intact between the watercourses.

NATURAL SUBDIVISIONS OF THE STATE, WITH THEIR TOPOGRAPHIC FEATURES, SOILS, MINERALS, AND OTHER RESOURCES.-The main topographical features of any region are the inequalities of surface caused either by actual folds or wrinkles in the earth's crust, or by the unequal degradation of the land by atmospheric or aqueous agencies. The two great factors which determine surface configuration are thus seen to be geological structure and erosion. In all cases, difference in the quality of the material acted upon by erosion is an important subfactor to which are due all those minor inequalities which constitute scenery.'

Under the action of the atmospheric and other agencies, rocks are disintegrated and converted into soils which either rest upon the parent rock or are removed by running water or other transporting agency and spread over regions more or less remote from their point of origin. A distinction is thus made between sedentary or residual soils and transported or drifted soils. We shall presently see that soils of the first class prevail in the Appalachian region, while the transported soils are more characteristic of the Coastal Plain.

In the present position or attitude of the rock strata, whether approximately horizontal or much inclined; in the nature of the connection between the topography and the geological structure; and in the relations of the soils to the country rock upon which they rest, are found the characters according to which, for convenience of description, the State may be marked off into the following subdivisions :

Divisions of the Appalachian Area.

These are four in number, viz. :

1. THE TALLADEGA MOUNTAINS AND ASHLAND PLATEAU.-These two sections correspond to the Blue Ridge and the Piedmont Plateau of Georgia and the States to the northeast, and make up the southeastern part of the Appalachian area of Alabama. The rocks are all more or less crystalline in texture, and are rarely in horizontal position, but nearly always highly inclined, generally towards the southeast. The Talladega Mountains, which make the northwestern part of this division, are high, sharp-crested ridges, with narrow, often gorge-like, valleys between.

From this elevated land, which carries some points 2,400 feet above sea level, the country falls rapidly towards the southeast, into the Ashland or Piedmont Plateau, with an average elevation of about 1,000 feet.

The plain-like character of this section is evidently the result of weathering and erosion, base-levelling, and is not due to the horizontal position of the rocks, as is the case in the Cumberland Plateau, presently

PHYSICAL GEOGRAPHY.

to be described. The present topographic features are due to the subsequent elevation of this plain and the dissection of its mass by the water

courses.

As types of the rocks of this section, granites, gneisses, and schists may be taken. The soils are all derived from the decay of the rocks of the country, upon which, in general, they directly rest. The most fertile of these soils are those derived from granites and gneisses, and they are red or gray in color as the parent rocks contain iron-bearing minerals or not. Nearly all the granitic soils have been long under cultivation, the first settlements having been where these soils prevailed.

The other class of rocks of this section, viz., the schists and slates, yield much less productive soils, and the face of the country where they prevail is also much more broken than in the granitic areas. For this reason, so directly dependent upon the nature of the underlying rocks, the population in the slate lands is less dense than in the granitic.

The mineral productions of this region are gold and copper ores, granite, soapstone, mica, corundum, and kaolin. The greater part of it is heavily timbered, usually with oak and short-leaf pine, but along the eastern flank of the Talladega Mountains there are large areas of the best of long-leaf pine timber.

2. THE COOSA VALLEY REGION.-The wide valley with prevailing calcareous soils, lying between the Talladega Mountains on the east and the coal fields on the west, has received this name from the river which drains it. It is the continuation of the valley of East Tennessee and the great valley of Virginia. The rocks which underlie the Coosa Valley, while mostly some form of limestone, include also sandstones and shales. They are no longer in their original horizontal position, but have been tilted, and inclined often at high angles, and very generally towards the southeast. In the erosion of this region, the limestones have yielded more than the other strata, and they therefore form the floors of the valleys, while the harder sandstones occupy the ridges. In consequence of this diversity of material, and the resulting diversity of topographic forms, the Coosa Valley is a complex trough fluted with scores of smaller parallel valleys and ridges. Of the same general character as the Coosa Valley are the outlying valleys, Cahaba, Wills's, Jones's, Murphree's, and the valley of Blount Springs. These are long, narrow valleys, running northeast and southwest, and due, like the Coosa Valley, to folds or plications of the earth's crust.

Throughout these valleys the soils rest directly upon the rocks from which they have been derived. Naturally, the soils derived from the limestones, the red clay soils, are the most fertile, and consequently have