Letters from the Alleghany Mountains

by Charles Lanman

C. L.

To the Editors of the National Intelligencer.

Ashville, North Carolina, October, 1848.

Gentlemen: As you have recently been publishing a series of letters in relation to that portion of the Alleghany range which is situated in North Carolina, you may, perhaps, find matter of interest in the subject of this communication. My purpose in making it is not only to present to the consideration of those learned or curious in geology facts singular and interesting in themselves, but also, by means of your widely disseminated paper, to stimulate an inquiry as to whether similar phenomena have been observed in any other parts of the Alleghany range.

A number of persons had stated to me that at different periods, within the recollection of persons now living, a portion of a certain mountain in Haywood county had been violently agitated and broken to pieces. The first of these shocks remembered by any person whom I have seen, occurred just prior to the last war with England, in the year 1811 or 1812. Since then some half a dozen or more have been noticed. The latest occurred something more than three years ago, on a clear summer morning. These shocks have usually occurred, or at least been more frequently observed, in calm weather. They have generally been heard distinctly by persons in the town of Waynesville, some twenty miles off. The sound is described as resembling the rumbling of distant thunder, but no shaking of the earth is felt at that distance. In the immediate vicinity of the mountain, and for four or five miles around, this sound is accompanied by a slight trembling of the earth, which continues as long as the sound lasts—that is, for one or two minutes. After each of these shocks the mountain was found to be freshly rent and broken in various places.

Having an opportunity afforded me a few days since, I paid a visit to the locality, and devoted a few hours to a hurried examination. It is situated in the northeastern section of Haywood county, near the head of Fine’s creek. The bed of the little creek at the mountain is probably elevated some twenty-six or seven hundred feet above the level of the ocean. The valley of the French Broad, at the Warm Springs, some fifteen miles distant, is twelve hundred feet lower. They are separated, however, by a mountain ridge of more than four thousand feet elevation above the sea, and there are high mountains in all directions around the locality in question. The immediate object of interest is the western termination of a mountain ridge nearly half a mile to the east of the house of Mr. Matthew Rogers. The top of this ridge, at the place where it has been recently convulsed, is some three or four hundred feet above the creek, at its western extremity, but it rises rapidly for some distance as it goes off to the eastward towards the higher mountain range. The northern side of this ridge I had not time to examine, but the marks of violence are observable at the top of the ridge, and extend in a direction nearly due south, down the side of the mountain four or five hundred yards, to a little branch; thence across it, over a flat or gentle slope, and up the side of the next ridge as far as I went, being for three or four hundred yards. The tract of ground examined by me was perhaps half a mile in length from north to south. The breadth of the surface subjected to violence was nowhere more than two hundred yards, and generally rather less than one hundred. Along this space the ground has been rent in various places. The fissures or cracks most frequently run in a northern and southern direction, and towards the tops of the mountains, but they are often at right angles to these, and in fact some may be found in all directions. While some of them are so narrow as to be barely visible, others are three or four feet in width. The annual falling of the leaves and the washing of the rains has filled them so that at no place are they more than five or six feet in depth. Along this tract all the large trees have been thrown down, and are lying in various directions, some of them six feet in diameter. One large poplar, which stood directly over one of the fissures, was cleft open, and one half of the trunk, to the height of more than twenty feet, is still standing. Though the fissure, which passed directly under its centre, is not more than an inch in width, it may be observed for nearly a hundred yards. All the roots of trees which crossed the lines of fracture are broken. The rocks are also cloven by these lines. The top of the ridge, which seems originally to have been an entire mass of granite, is broken in places. Not only have those masses of rock, which are chiefly under ground, been cleft open, but fragments lying on the surface have been shattered. All those persons who have visited it immediately after a convulsion, concur in saying that every fallen tree and rock has been moved. The smallest fragments have been thrown from their beds as though they had been lifted up. In confirmation of this statement I observed that a large block of granite, of an oblong form, which, from its size, must have weighed not less than two thousand tons, had been broken into three pieces of nearly equal size. This mass was lying loosely on the top of the ground, in a place nearly level, and there were no signs of its having rolled or slidden. The fragments were separated only a few inches, rendering it almost certain that it had been broken by a sudden shock or jar, which did not continue long enough to throw the pieces far apart.

Some parts of the surface of the earth have sunk down irregularly a few feet, other portions have been raised. There are a number of little elevations or hillocks, some of a few feet only in extent, and others twenty and thirty yards over. The largest rise at the centre to the height of eight or ten feet, and slope gradually down; some of these have been surrounded on all sides by a fissure, which is not yet entirely filled up. In some instances the trees on their sides, none of them large, are bent considerably from the perpendicular, showing that they had attained some size before the change of level took place on the surface where they grow.

The sides of the mountain generally are covered by a good vegetable mould, not particularly rocky, and sustaining trees of large size. But along the belt of convulsion the rocks are much more abundant, and there are only young trees growing, the elasticity of which enabled them to stand during the shocks.

With reference to the mineral structure of the locality, it may be remarked that that entire section seems to constitute a hypogene formation. It consists of granites, gneiss, sometimes porphyritic, hornblende rock, micaceous schists, clay slate, and various other metamorphic strata. The nearest aqueous rocks that I know of are the conglomerate sandstone and sedimentary limestone, in the vicinity of the Warm Springs, fifteen miles distant in a direct line. If any volcanic rock has been found in hundreds of miles I am not aware of it. The mountain itself bears the most indubitable marks of plutonic origin. It consists mainly of a grayish white granite, in which the felspar greatly predominates, but it is sometimes rendered dark by an excess of mica in minute black scales. This latter mineral I saw also there in small rather irregular crystals. Some portions of the rock contained, however, its three ingredients, in nearly equal proportions; the quartz, in color, frequently approaching ash gray. In several places I observed that the granite was cut vertically by veins of gray translucent quartz, of from one to six inches in thickness. There were also lying in places on the ground lumps of common opaque white quartz, intersected by narrow veins, not exceeding half an inch in thickness, of specular iron, of the highest degree of brilliancy and hardness that that mineral is capable of possessing. It may be remarked that there are, in different directions within two miles of the locality, two considerable deposits of magnetic iron ore. The only rock which I observed there possessing any appearance of stratification seems to consist of mica, hornblende and a little felspar, in a state of intimate mixture. Having but a few hours to remain there, I do not pretend that there are not many other minerals at the locality; but I have no doubt but that the predominating character of the formation is such as I have endeavored to describe it, and I have been thus minute, in order that others may be able to judge more accurately in relation to the cause of the disturbances.

Before visiting the locality I supposed that the phenomena might be produced by the giving way of some part of the base of the mountain, so as to produce a sinking or sliding of the parts; but a moment’s examination was decisive on this point. It not unfrequently happens that aqueous rocks rest on beds of clay, gravel, &c., which may be removed from underneath them by the action of running water or other causes. Cavities are thus produced, and it sometimes happens that considerable bodies of secondary limestone and other sedimentary strata sink down with a violent shock. This, however, is found to be true only of such strata as are deposited from water. But at the locality under consideration the rocks are exclusively of igneous origin, and, I may add, two of the class termed hypogene or “netherformed.” For though felspar and hornblende have been found in the lower parts of some of the lavas, where the mass had been subjected to great pressure and cooled slowly, yet quartz and mica have never been found as constituents of any volcanic rock, not even in the basaltic dikes and injected traps, where there must have been a pressure equal to several hundred atmospheres. It is universally conceded by geologists that those rocks of which these minerals constitute a principal part, have been produced at great depths in the earth, where they were subjected to enormous pressure during their slow cooling and crystallization. Prior, therefore, to the denudation which has exposed these masses of granite to our view, they must have been overlaid and pressed down while in a fluid state by superincumbent strata of great thickness and vast weight. It is not probable, therefore, that any cavities could exist, nor, even if it were possible that such could be the case, is it at all likely that a granite arch which once upheld such an immense weight would in our day give way under the simple pressure of the atmosphere; or, even if we were to adopt the improbable supposition that the mass of granite composing this mountain had been formed at a great depth below the present surface of the earth, and forced up bodily by plutonic action, there is as little reason to believe that any cavities could exist. In fact, they are never found under granites. On looking at the surface of the ground at this place there is no appearance to indicate any general sinking of the mass. At the top of the ridge, where the fractures are observable across it, there is no variation in the slope of the surface or depression of the broken parts. Immediately below it, where the mountain has great steepness, equal at least to an inclination of forty-five degrees, where the line of fracture is parallel to the direction of the ridge, the surface is sunk suddenly ten or fifteen feet. This state of things, however, would inevitably be produced at such an inclination by the force of gravity alone, causing the parts separated by the shock to sink somewhat as they descend the mountain side. Lower down, where the steepness is not so great, the elevations much exceed the depressions. The same is true of the appearances on the south side of the branch, where the surface is almost level for several hundred yards; and I think that any one surveying the whole of the disturbed ground will be brought to the conclusion that there has been a general upheaval rather than a depression, and that the irregularities now observable are due to a force acting from below, which has, during the shocks, unequally raised different parts of the surface. One of the earlier geologists, while this science was in its infancy, would probably have ascribed these phenomena to the presence underneath the surface of a bed of pyrites, bituminous shale, or some other substances capable of spontaneous combustion, which had taken fire from being penetrated by a stream of water or some other accidental cause. If such a combustion were to take place at a considerable depth below the surface, and should to a great extent heat the strata above, they would thereby be expanded and thickened so as to be forced upward. Such an expansion, though it would be less in granite than in some other strata, as shown by your fellow-townsman, Col. Totten, would nevertheless, if the heated mass were thick and the elevation of temperature considerable, be sufficient to raise the surface as much as it appears to have been elevated; such expansion, however, being necessarily from its nature very gradual, would not account for the various violent shocks nor for the irregular action at the surface. On the other hand, if the burning mass were near the surface, so as to cause explosion by means of gases generated from time to time, it is scarcely conceivable that such gases, while escaping through fissures of the rock above, should fail to be observed, inasmuch as a great volume would be necessary to supply the requisite amount of force, nor is it at all probable that such a state of things would not be accompanied by a sensible change of temperature at the surface. The difficulty in the way of such a supposition is greatly increased when we consider the form of the long narrow belt acted on, and from the recurrence of the sudden violent shocks after long intervals of quiet. Such a hypothesis in fact I do not regard as entitled to more respect than another one which was suggested to me at the place. As it has no other merit than that of originality, I should not have thought it worth repeating but for the statement of fact made in support of it. While I was observing the locality, my attention was directed to an elderly man who was gliding with a stealthy step through the forest, carrying on his left shoulder a rifle, and in his right hand a small hoe, such as the diggers of ginseng use. His glances, alternating between the distant ridges and the plants about his feet, showed that while looking for deer he was not unmindful of the wants of the inhabitants of the Celestial Empire. On my questioning him in relation to the appearances, he said that he had observed them often after the different shocks; that the appearances were changed each time at the surface; that I ought to see it just after a shock, before the rain and leaves had filled the cracks, adding that it did “not show at all now.” He expressed a decided opinion that the convulsions were produced by silver under the surface. On my remarking that though I knew that that metal, in the hands of men, was an effective agent in cleaving rocks and excavating the earth, yet I had not supposed it could exert such an influence when deeply buried under ground, he stated in support of his opinion, that one of his neighbors had, on the north side of the mountain, found a spring hot enough to boil an egg. He also added that some three years since he had seen on the mountain, two miles to the north of this one, but in the direction seemingly of the line of force, a blazing fire for several hours, rising up sometimes as high as the tops of the trees, and going out suddenly for a moment at a time at frequent intervals. He declared that at the distance of a mile from where he was, the brightness was sufficient to enable him to see small objects. Several other persons in the vicinity I found subsequently professed to have seen the same light from different points of view, and described it in a similar manner. As no one of them seems to have thought enough of the matter to induce him to attempt to approach the place, though some persons represented that they had subsequently found a great quantity of “cinder” at the point, the statement of fact is not perhaps entitled to more weight than the hypothesis it was intended to support.