National Geographic Magazine/Volume 1/Number 4/Round about Asheville

by Bailey Willis

SECTION FROM THE CUMBERLAND PLATEAU TO THE BLUE RIDGE

Natural Profiles

ROUND ABOUT ASHEVILLE.

By Bailey Willis.

A broad amphitheatre lies in the heart of the North Carolina mountains which form its encircling walls; its length is forty miles from north to south and its width ten to twenty miles. At its southern gate the French Broad river enters; through the northern gate the same river flows out, augmented by the many streams of its extensive watershed.

From these water-courses the even arena once arose with gentle slope to the surrounding heights and that surface, did it now exist, would make this region a very garden, marked by its genial climate and adequate rainfall. But that level floor exists no longer; in it the rivers first sunk their channels, their tributaries followed, the gullies by which the waters gathered deepened, and the old plain was thus dissected. It is now only visible from those points of view from which remnants of its surface fall into a common plane of vision. This is the case whenever the observer stands upon the level of the old arena; he may then sweep with a glance the profile of a geographic condition which has long since passed away.

Asheville is built upon a bit of this plain between the ravines of the French Broad and Swannanoa rivers, now flowing 380 feet below the level, and at the foot of the Beau-catcher hills; toward which the ground rises gently. The position is a commanding one, not only for the far reaching view, but also as the meeting place of lines of travel from north, south, east, and west. Thus Asheville became a town of local importance long before railroads were projected along the lines of the old turnpikes. The village was the center of western North Carolina, as well of the county of Buncombe, and was therefore appropriately the home of the district Federal court. A May session of the court was in progress nine years ago when I rode up the muddy street from the Swannanoa valley. Several well-known moonshiners were on trial, and the town street was crowded with their sympathizers, lean mountaineers in blue and butternut homespun. Horses were hitched at every available rack and fence, and horse trading was active. Whiskey was on trial at other bars than that of the court, and the long rifle, powder-horn and pouch had not been left in the mountains. To a "tenderfoot" (who had the day before been mistaken for a rabbit or a revenue officer!) the attentions of the crowd were not reassuring.

The general opinion was, I felt, akin to that long afterward expressed by Groundhog Cayce: "It air an awful thing ter kill a man by accident;" and I staid but a very short time in Asheville.

Riding away toward the sunset, I traversed the old plain without seeing that it had had a continuous surface. I noted the many gullies, and I lost in the multitude of details the wide level from which they were carved. That the broader fact should be obscured by the many lesser ones is no rare experience, and perhaps there is no class of observations of which this has been more generally true than of those involved in landscape study. But when once the Asheville plain has been recognized, it can never again be ignored. It enters into every view, both as an element of beauty and as evidence of change in the conditions which determine topographic forms. Seldom in the mountains can one get that distance of wooded level, rarely is the foreground so like a gem proportioned to its setting; all about Asheville one meets with glimpses of river and valley, sunken in reach beyond reach of woodland which stretch away to the blue mountains. The even ridges form natural roadsites, and in driving one comes ever and anon upon a fresh view down upon the stream far across the plain and up to the heights. And to the student of Appalachian history, the dissected plain is a significant contradiction of the time honored phrase, "the everlasting hills." That plain was a fact, the result of definite conditions of erosion; it exists no more in consequence of changes. What were the original conditions? In what manner have they changed? Let us take account of certain other facts before suggesting an answer. Of the mountains which wall the Asheville amphitheatre, the Blue Ridge on the east and the Unaka chain on the west are the two important ranges. The Blue Ridge forms the divide between the tributaries of the Atlantic and those of the Gulf of Mexico, and the streams which flow westward from it all pass through the Unaka chain. It would be reasonable to suppose that the rivers rose in the higher and flowed through the lower of the two ranges, but they do not. The Blue Ridge is an irregular, inconspicuous elevation but little over 4000 feet above the sea; the Unaka mountains form a massive chain from 5000 to 6500 feet in height. That streams should thus flow through mountains higher than their source was once explained by the assumption that they found passage through rents produced by earth convulsions; but that vague guess marked the early and insufficient appreciation of the power of streams as channel cutters, and it has passed discredited into the history of our knowledge of valley-formation. That rivers carve out the deepest cañons, as well as the broadest valleys, is now a truism which we must accept in framing hypotheses to account for the courses of the French Broad and other similar streams. Moreover, since waters from a lower Blue Ridge could never of their own impulse have flowed over the higher Unaka, we are brought to the question, was the Blue Ridge once the higher, or have streams working on the western slope of the Unaka range (when it was a main divide), worn it through from west to east, capturing all that broad watershed between the two mountain ranges? Either hypothesis is within the possibility of well established river action, and both suggest the possibility of infinite change in mountain forms and river systems. Without attempting here to discriminate between these two hypotheses, for which a broader foundation of facts is needed, let us look at the channel of the French Broad below Asheville, in the river's course through the range that is higher than its source. Descending from the old plain into the river's ravine, we at once lose all extended views and are closely shut in by wooded slopes and rocky bluffs. The river falls the more rapidly as we descend, and its tributaries leap to join it, the railroad scarce finding room between the rocks and the brawling current. The way is into a rugged and inhospitable gorge whose walls rise at last on either hand into mountains that culminate some thirty miles below Asheville. At Mountain Island the waters dash beautifully over a ledge of conglomerate and rush out from a long series of rapids into the deep water above Hot Springs. Beyond the limestone cove in which the springs occur, the valley, though narrow still, is wider and bottom lands appear. Thus the water gap of the French Broad through the Unakas is narrow and rugged, the river itself a tossing torrent; but had we passed down other streams of similar course, we should have found them even more turbulent, their channels even more sharply carved in the hard rocks. On Pigeon river there are many cliffs of polished quartzite, and on the Nolichucky river a V-shaped gorge some eight miles long is terraced where the ledges of quartzite are horizontal and is turreted with fantastic forms where the strata are vertical. Where the river valleys are of this sharp cut character in high mountains, the abrupt slopes, cliffs and rocky pinnacles are commonly still more sharply accented in the heights. The Alpine tourist or the mountaineer of the Sierras would expect to climb from these cañons to ragged combs or to scarcely accessible needle-like peaks. But how different from the heights of the Jungfrau are the "balds" of the Unakas! like the iceworn granite domes of New England, the massive balds present a rounded profile against the sky. Although composed of the hardest rock, they yet resemble in their contours, the low relief of a limestone area. Broad, even surfaces, on which rocky outcrops are few and over which a deep loam prevails, suggest rather that one is wandering over a plain than on a great mountain; yet you may sweep the entire horizon and find few higher peaks. The view is often very beautiful, it is far-reaching, not grand. No crags tower skyward, but many domes rise nearly to the same heights, and dome-like, their slopes are steepest toward the base. The valleys and the mountains have exchanged the characters they usually bear; the former are dark and forbidding, wild and inaccessible, the latter are broad and sunlit of softened form, habitable and inhabited. All roads and villages are on the heights, only passing travelers and those who prey upon them frequent the depths.

These facts of form are not local, they are general: all the streams of the Unaka mountains share the features of the French Broad Cañon, while peaks like Great Roan, Big Bald, Mt. Guyot, are but examples of a massive mountain form common throughout the range.

Thus the Unaka chain presents two peculiar facts for our consideration; it is cut through by streams rising in a lower range, and its profiles of erosion are convex upward not downward.

If we follow our river's course beyond the Unaka chain into the valley of East Tennessee we shall still find the channel deeply cut; here and there bottomlands appear, now on one side, now on the other, but the banks are more often steep slopes or vertical cliffs from fifty to one hundred feet high. The creeks and brooks meander with moderate fall through the undulating sur face of the valley, but they all plunge by a more or less abrupt cascade into the main rivers. It is thus evident that the tributaries cannot keep pace with the rivers in channel-cutting, and the latter will continue to sink below the surface of general degradation until their diminished fall reduces their rate of corrasion below that of the confluent streams.

If from topographic forms we turn to consider the materials, the rocks, of which they are composed, we shall find a general rule of relation between relative elevation and rock-hardness. Thus the great valley of East Tennessee has a general surface 3000 feet below the mean height of the Unakas: it is an area of easily soluble, often soft, calcareous rocks, while the mountains, consist of the most insoluble, the hardest, silicious rocks. East of the Unakas the surface is again lower, including the irregular divide, the Blue Ridge; here also, the feldspathic gneisses and mica schists are, relatively speaking, easily soluble, and non-coherent. What is thus broadly true is true in detail, also where a more silicious limestone or a sandstone bed occurs in the valley it forms a greater or less elevation above the surface of the soft rocks; where a more soluble, less coherent stratum crops out in the mountain mass, a hollow, a cove, corresponds to it. Of valley ridges, Clinch mountain is the most conspicuous example; of mountain hollows the French Broad valley at Hot Springs, or Tuckaleechee Cove beneath the Great Smoky mountain, is a fair illustration.

But impassive rock-hardness, mere ability to resist, is not adequate to raise mountains, nor is rock-softness an active agent in the formation of valleys. The passive attitude of the rocks implies a force, that is resisted, and the very terms in which that attitude is expressed suggest the agent which applies the force. Hardness, coherence, insolubility,—these are terms suggestive of resistance to a force applied to wear away, to dissolve, as flowing water wears by virtue of the sediment it carries and as percolating waters take the soluble constituent of rocks into solution. And it is by the slow mechanical and chemical action of water that not only cañons are carved but even mountain ranges reduced to gentle slopes.

If we designate this process by the word "degradation," it follows from the relation of resistance to elevation in the region under discussion that we may say: The Appalachians are mountains of differential degradation; that is, heights remain where the rocks have been least energetically acted on, valleys are carved where the action of water has been most effective.

In order that the process of degradation may go on it is essential that a land mass be somewhat raised above the sea, and, since the process is a never-ceasing one while streams have sufficient fall to carry sediment, it follows that, given time enough, every land surface must be degraded to a sloping plain, to what has been called a base level.

With these ideas of mountain genesis and waste, let us consider some phases of degradation in relation to topographic forms; and in doing so I cannot do better than to use the terms employed by Prof. Wm. M. Davis.

When a land surface rises from the ocean the stream systems which at once develope, are set the task of carrying back to the sea all that stands above it. According to the amount of this alloted work that streams have accomplished, they may be said to be young, mature or aged; and if, their task once nearly completed, another uplift raise more material to be carried off, they may be said to be revived. These terms apply equally to the land-surface, and each period of development is characterized by certain topographic forms.

In youth simple stream systems sunk in steep walled cañons are separated by broad areas of surface incompletely drained. In maturity complex stream systems extend branches up to every part of the surface; steep slopes, sharp divides, pyramidal peaks express the rapidity with which every portion of the surface is attacked.

In old age the gently rolling surface is traversed by many quiet flowing streams; the heights are gone, the profiles are rounded, the contours subdued. In the first emergence from the sea the courses of streams are determined by accidents of slope, it may be by folding of the rising surface into troughs and arches. During maturity the process of retrogressive erosion, by which a stream cuts back into the watershed of a less powerful opponent stream, adjusts the channels to the outcrops of soft rocks and leaves the harder strata as eminences. In old age this process of differential degradation is complete and only the hardest rocks maintain a slight relief.

Suppose that an aged surface of this character be revived: the rivers hitherto flowing quietly in broad plains will find their fall increased in their lower courses; their channels in soft rock will rapidly become cañons, and the revived phase will retreat up stream in the same manner that the cañons of youth extended back into the first uplifted mass. If the area of soft rocks be bounded by a considerable mass of very hard rocks, it is conceivable that a second phase of age, a base level, might creep over the valley while yet the summits of the first old age remained unattacked, and should perchance revival succeed revival the record of the last uplift might be read in sharp cut channels of the great rivers, while the forms of each preceding phase led like steps to the still surviving domes of that earliest old age.

Is there aught in these speculations to fit our facts? I think there is. We have seen that our mountains and valleys are the result of differential degradation, and that this is not only broadly true but true in detail also. This is evidence that streams have been long at work adjusting their channels, they have passed through the period of maturity.

We have climbed to the summits of the Unakas and found them composed of rocks as hard as those from which the pinnacle of the Matterhorn is chiseled; but we see them gently sloping, as a plain. These summits are very, very old.

We have recognized that dissected plain, the level of the Asheville amphitheatre, now 2,400 feet above the sea; it was a surface produced by subaerial erosion, and as such it is evidence of the fact that the French Broad River, and such of its tributaries as drain this area, at one time completed their work upon it, reached a base level. That they should have accomplished this the level of discharge of the sculpturing streams must have been constant during a long period, a condition which implies either that the fall from the Asheville plain to the ocean was then much less than it now is, or that through local causes the French Broad was held by a natural dam, where it cuts the Unaka chain.

If we should find that other rivers of this region have carved the forms of age upon the surfaces of their intermontane valleys, and there is now some evidence of this kind at hand, then we must appeal to the more general cause of base-levelling and accept the conclusion that the land stood lower in relation to the ocean than it now does. Furthermore, we have traversed the ravines which the streams have cut in this ancient plain and we may note on the accompanying atlas sheet that the branches extend back into every part of it; the ravines themselves prove that the level of discharge has been lowered, the streams have been revived; and the wide ramification of the brooks is the characteristic of approaching maturity.

We have also glanced at the topography of the valley and have found the rivers flowing in deep-cut simple channels which are young, and the smaller streams working on an undulating surface that is very sensitive to processes of degradation.

The minor stream systems are very intricate and apparently mature, but they have not yet destroyed the evidence of a general level to which the whole limestone area was once reduced, but which now is represented by many elevations that approach 1,600 feet above the sea. Here then in the valley are young river channels, mature stream systems and faint traces of an earlier base level, all of them more recent than the Asheville level, which is in turn less ancient than the dome-like summits of the Unakas.

What history can we read in these suggestive topographic forms and their relations?

The first step in the evolution of a continent is its elevation above the sea. The geologist tells us that the earliest uplift of the Appalachian region after the close of the Carboniferous period was preceded or accompanied by a folding of the earth's crust into mountainous wave-like arches; upon these erosion at once began and these formed our first mountains. Where they were highest the geologist may infer from geologic structure and the outcrops of the oldest rocks; but the facts for that inference are not yet all gathered and it can only be said that the heights of that ancient topography were probably as great over the valley of Tennesseee as over the Unaka chain. The positions of rivers were determined by the relations of the arches to each other and, as they were in a general way parallel, extending from northeast to southwest, we know that the rivers too had northeast-southwest courses. From that first drainage system the Tennessee river, as far down as Chattanooga, is directly descended, and when the geologic structure of North Carolina and East Tennessee is known, we may be able to trace the steps of adjustment by which the many waters have been concentrated to form that great river. At present we cannot sketch the details, but we know that it was a long process and that it was accompanied by a change in the raison d'être of the mountain ranges. The first mountains were high because they had been relatively raised; they gave place to hills that survived because they had not been worn down. A topography of differential uplift gave place to one of differential degradation. And to the latter the dome-like "balds" of the Unakas belong. Those massive summits of granite, quartzite and conglomerate are not now cut by running waters; they are covered with a mantel of residual soil, the product of excessively slow disintegration, and they are the remnants of a surface all of which has yielded to degradation, save them. In time the streams will cut back and carve jagged peaks from their masses, but standing on their heights my thought has turned to the condition they represent—the condition that is past. And thus in thought I have looked from the Big Bald out on a gently sloping plain which covered the many domes of nearly equal height and stretched away to merge on the horizon in the level of the sea. That, I conceive, was the first base level plain of which we have any evidence in the Appalachians and from that plain our present valleys have been eroded. The continental elevation must then have been 3,000 or 4,000 feet less than it is now, and the highest hills were probably not more than 2,500 feet above the sea. This was perhaps a period of constant relation between sea and land, but it was succeeded by one during which the land slowly rose. The rivers, which had probably assumed nearly their present courses, were revived; the important channels soon sank in cañons, the tributaries leaped in rapids and cut back into the old base level. The region continued to rise during a period long enough to produce the essential features of the mountain ranges of to-day; then it stood still in relation to the sea or perhaps subsided somewhat, and the French Broad and probably other rivers made record of the pause in plains like that about Asheville. Again the land rose slowly; again it paused, and rivers, working always from their mouths backward, carved a base-level in the limestones of the great valley; but before that level could extend up through the gorges in the Unakas, the continent was raised to its present elevation, the streams responded to the increased fall given them and the rivers in the valley began to cut their still incomplete cañons.

Are we not led step by step from these latest sharply cut channels up stream through the chapters of erosion to the still surviving domes of an early old age? Let us sum up the history we have traced. There is reason to believe that:

1st. The consequent topography of the earliest Appalachian uplift was entirely removed during a prolonged period of erosion and was replaced by a relief of differential degradation.

2d. The balds of the Unakas represent the heights of that first-known approach to a base-level.

3d. The topography of the region has been revived by a general, though not necessarily uniform, uplift of 3,000 feet or more, divided by two intervals of rest; during the first of these the Asheville base-level was formed; during the second, the valley alone was reduced.

4th. The latest movement of the uplift has been, geologically speaking, quite recent, and the revived streams have accomplished but a small part of their new task.

These conclusions are reached on the observation of a single class of facts in one district; they must be compared with the record of continental oscillation on the sea coasts, in the deposits of the coastal plain, and in the topography of other districts.

The history of the Appalachians is written in every river system and on every mountain range, but in characters determined for each locality by the local conditions. Only when the knowledge, to which every tourist may contribute, is extended over the entire region shall we know conclusively the whole story.