Letters from the Alleghany Mountains

by Charles Lanman

It is probable, however, that some difficulty will attend any explanation that can be offered in relation to the phenomena at this place. We know that the elevation of the surface of the earth is at many places undergoing a change, so gradual as not to be observed at any one time. Some of the northwestern parts of Europe, for example, are experiencing a slow upheaval equal to five or six feet in a century, while on the coast of Greenland the subsidence, or depression, is such that even the ignorant inhabitants have learned that it is not prudent for them to build their huts near the edge of the water. Similar changes are observed in various other places, but they obviously bear no analogy to the facts under consideration. Again, it is well known that earthquakes from time to time agitate violently portions of the earth’s surface, of greater or less extent; that while one single shock has permanently raised two or three feet the coast of Chili for several hundred miles, others have elevated or depressed comparatively small spaces. It usually happens, however, that when the shock is so forcible at one point as to break the solid strata of the globe, the surrounding parts are violently agitated for a considerable distance. In the present instance, however, the shock for half a mile at least in length, and for the breadth of one hundred yards, is such as to cleave a mass of granite of seemingly indefinite extent, and so quick and sudden as to displace the smallest fragments on the surface; and yet at the house of Mr. Rogers, less than half a mile distant, a slight trembling only is felt, not sufficient to excite alarm, while at the distance of a few miles, though the sound is heard, no agitation of the ground is felt. Should we adopt the view of those who maintain that all the central parts of the earth are in a state of fusion, and that violent movements of parts of the melted mass give rise to the shocks which are felt at the surface, the explanation of this and similar phenomena is still not free from difficulty. Upon the supposition that the solid crust of the globe has no greater thickness than that assumed by Humboldt, some twenty-odd miles, it would scarcely seem that such a crust, composed of rocky strata, would have the requisite degree of elasticity to propagate a violent shock to so small a surface, without a greater agitation of the surrounding parts than is sometimes observed. Volcanic eruptions, however, take place through every variety of strata; but these volcanoes are rarely if ever isolated; on the contrary, not only the volcanoes now active, but such as have been in a state of rest from the earliest historic era, are distributed along certain great lines of force, or belts, the limits of which seem to have been pretty well defined by geologists. But I am not aware of there being any evidence afforded of volcanic action, either in recent or remote geological ages, within hundreds of miles of this locality. Even if such exist beneath the sea, it must be at least two hundred miles distant. If then we attribute these convulsions to the same causes which have elsewhere generated earthquakes and volcanoes, is it probable that this is the only point in the Alleghany range thus acted on? The fact that nothing else of the kind has been, as far as I know, published to the world, is by no means conclusive, since the disturbances here have not only been unnoticed by writers, but are even unknown to nine-tenths of those persons living within fifty miles of the spot. Is it then improbable that different points of the great mountain range are sensibly acted on from year to year? It is true that this may be the only locality affected. It might be supposed that there is at this place a mass of rock, separated wholly or partially from the adjoining strata, reaching to a great depth, and resting on a fluid basin, the agitation of which occasionally would give a shock to the mass. Though such be not at all probable, yet it is conceivable that such a mass might possess the requisite shape; and if at the top, instead of being a single piece, it should have a number of irregular fragments resting on it below the surface, then it might be capable of producing inequalities observable after each successive convulsion. From the form, however, of the belt acted on, as well as from other considerations, such a hypothesis is only possible, not probable. It would perhaps more readily be conceded that there was in the solid strata below an oblong opening, or wide fissure, connected with the fluid basin below, and filled either with melted lava, or more probably with elastic gas, condensed under vast pressure, so that the occasional agitations below would be propagated to the surface at this spot. Or if we suppose that steam, at a high heat, or some of the other elastic gaseous substances, should escape through fissures from the depths below, but have their course obstructed near the surface, so as to accumulate from time to time, until their force was sufficient to overpower the resistance, then a succession of periodic explosions might occur. Such a state of things would be analogous to the manner in which Mr. Lyell accounts for the Geysers, or Intermittent Hot Springs, in Iceland, except that the intervals between the explosions in this instance are much greater than in the other. It is easy to conceive that the shocks of some former earthquakes may have produced the requisite condition in the strata at that place.

Or, should we reject all such suppositions, it might be worth while to inquire whether this and similar phenomena may not be due to electricity? The opinion seems to have become general with men of science, that there are great currents of electricity circulating in the shell of the globe, mainly if not entirely in directions parallel to the magnetic equator. The observations and experiments of Mr. Fox have, in the opinion of a geologist so eminent as Mr. Lyell, established the fact that there are electro-magnetic currents along metalliferous veins. Taking these things to be true, it may well be that the electricity in its passage should be collected and concentrated along certain great veins. During any commotion in the great ocean of electricity, the currents along such lines, or rather where they are interrupted, might give rise to sensible shocks. The exceedingly quick vibratory motion, often observed on such occasions, seems analogous to some of the observed effects of electricity. In the present instance the line of force appears to coincide with the direction of the magnetic needle. It is also represented that the sound accompanying the convulsions is heard more distinctly at Waynesville, twenty miles south, than it is within two or three miles to the east or west of the locality, seeming to imply that the force may be exerted in a long line, though it is more intense at a particular point. In adverting, however, to the manner in which the phenomena observed at this place might possibly be accounted for, it is not my expectation to be able to arrive at their cause. One whose attention is mainly directed to political affairs, and who at most gets but an occasional glimpse of a book of science, ought neither to assume, nor to be expected to accomplish this. I have adopted the above mode of making suggestions as to the causes, solely to enable me to explain the facts observed in a more intelligible manner than I could do by a mere detail of the appearances and events as narrated. Perhaps those whose minds are chiefly occupied with the consideration of such subjects will find an easy solution of these phenomena. Should this letter be instrumental in eliciting information in relation to similar disturbances elsewhere in the Alleghany range, then its publication may answer some valuable purpose.

Very respectfully, yours, T. L. CLINGMAN.

Messrs. Gales & Seaton.

P. S. Since writing this letter, I have been apprized of a similar convulsion which occurred six or seven years ago, at a place some forty miles distant from this in a southwesterly direction. My informant says that at his house the ground was agitated for some minutes during a rumbling sound, and that a few miles off, the earth was rent and broken for the distance of two miles in length and nearly a half mile in breadth. Though I have not seen the locality, I have no doubt of the truth of the statement, nor of the general resemblance of the phenomena to those I have described above.

T. L. C.

To J. S. Skinner, Esq.

House of Representatives, Feb. 3, 1844.

Dear Sir: Your favor of the 30th ultimo was received a day or two since, and I now avail myself of the very first opportunity to answer it. I do so most cheerfully, because, in the first place, I am happy to have it in my power to gratify in any manner one who has done so much as yourself to diffuse correct information on subjects most important to the agriculture of the country; and, secondly, because I feel a deep interest in the subject to which your inquiries are directed.

You state that you have directed some attention to the sheep husbandry of the United States, in the course of which it has occurred to you that the people of the mountain regions of North Carolina, and some of the other Southern States, have not availed themselves sufficiently of their natural advantages for the production of sheep. Being myself well acquainted with the western section of North Carolina, I may perhaps be able to give you most of the information you desire. As you have directed several of your inquiries to the county of Yancey, (I presume from the fact, well known to you, that it contains the highest mountains in any of the United States,) I will, in the first place, turn my attention to that county. First, as to its elevation. Dr. Mitchell, of our University, ascertained that the bed of Tow river, the largest stream in the county, and at a ford near its centre, was about twenty-two hundred feet above the level of the ocean. Burnsville, the seat of the court-house, he found to be between 2,800 and 2,900 feet above it. The general level of the county is, of course, much above this elevation. In fact, a number of the mountain summits rise above the height of six thousand feet. The climate is delightfully cool during the summer: there being very few places in the county where the thermometer rises above 80° on the hottest day. An intelligent gentleman who passed a summer in the northern part of the county (rather the more elevated portion of it) informed me that the thermometer did not rise on the hottest days above 76°.