as well as from its greater original magnitude, the annual simple harmonic wave becomes more and more predominant as we descend, and the curve of temperature for the year approaches more and more nearly to the form of a simple harmonic curve, or curve of sines.

"Observations taken at three stations in or near Edinburgh, and at Greenwich Observatory, have been reduced in accordance with the above principles, the result being in every case to show a satisfactory agreement between theory and practice; and the values of the thermal coefficient thus obtained for these four stations, have furnished the basis

of the most reliable calculations yet made regarding the earth's age as a habitable globe. For the three Edinburgh stations the value of c (which is the product of specific heat by specific gravity) was also determined by laboratory experiments conducted by Regnault, and hence the conductivity, k, was found by computation.

"The following is a sample of the temperatures observed at Greenwich at the depths of 1 inch, 12.8 feet, and 25.6 feet. The warmest and coldest calendar months had the following mean temperatures:

"The mean temperature at a depth of 10, 20, or 30 feet does not differ much from the mean temperature at the surface. A slight increase is, however, usually observable even at these small depths; and, when we penetrate to the depth of several hundred feet, we find the temperature higher by several degrees than the mean temperature of the surface. In fact, the deeper we go the higher is the temperature which we find. "Attempts were formerly made to explain away this phenomenon, the high temperatures observed in deep mines being ascribed to the pres ence of the men working in them, assisted in some cases by the slow combustion of pyrites; but the fact of a steady increase downward, at a rate which is not exactly uniform, but varies from about 1° Fahr. in 100 feet to 10 Fahr. in 40 feet, has now been placed beyond all question."

Theoretical investigations will be found in Fourier's Théorie analytique de la chaleur, Paris, 1822; in Poisson's Traité mathématique de la chaleur, Paris, 1835. See also various papers by Quetelet in the Mém. de l'Acad. roy. de Bruxelles; also, Piazzi Smyth in Astronomical Observations at the Royal Observatory at Edinburgh; Forbes and his own Observations, vol. xi, for 1849-254, and vol. xiii, for 1860-'70. A fair statement of the subject is found in Schmid's Meteorology, Leipsic, 1860. See, also, J. D. Forbes's "Experiments on the Temperature of the Earth," in Trans. R. S. E., 1846; Sir W. Thomson "On the Reduction of Observations of Underground Temperature," in Trans. R. S. E., 1860; “On the Age of the Sun's Heat," in Macmillan's Magazine, March, 1862; "On

the Secular Cooling of the Earth," in Trans. R. S. E., 1862, (reprinted at the end of Thomson and Tait's "Treatise on Natural Philosophy;") "The Doctrine of Uniformity in Geology Briefly Refuted," in Proc. R. S. E., December, 1865; "On Geological Time," in Trans. Geol. Soc., Glasgow, vol. III, part I; "Of Geological Dynamics," in Trans. Geol. Soc., Glasgow, vol. III, part II; J. D. Everett "On a Method of Reducing Observations of Underground Temperature," in Trans. R. S. E., 1860; "On the Mean Temperature of a Stratum of Soil," in Trans. R. S. E., 1862; "Reduction of the Observations of the Deep-sunk Thermometers," in Greenwich Observations, 1860; "Reports of Committee on Rate of Increase of Underground Temperature," in B. A. Reports, from 1868 onward.

ON A SERIES OF EARTHQUAKES IN NORTH CAROLINA, COMMENCING ON THE 10TH OF FEBRUARY, 1874.

BY PROFESSOR WARREN DU PRÉ,

Of Wofford College, Spartanburgh, S. C.

The following is an extract from a letter of the 24th April, 1874, from Professor Du Pré to General Benjamin Alvord, U. S. Army:

"My visit to the mountains of North Carolina was undertaken to satisfy myself with respect to the numerous rumors which had reached us of the volcanic disturbances in that section of the country. I could spend but two days (19th and 20th March) in the investigation, but was quite diligent in collecting facts and in extending my explorations on horse and on foot so as to cover a distance of eighteen or twenty miles. I was soon convinced that the physical disturbances were real, but many of the rumors were false, and that the truth had been much exaggerated by the fears of the people. The explosive noises accompanying the shocks and the limited area of the disturbances are peculiarities worthy the attention of scientists, and demand a more thorough exploration. The inclosed is a hasty report of my trip, which I drew up to allay, if possible, the fears of the inhabitants of the district.

Stone Mountain, the site of the disturbances, like all the neighboring peaks, is composed chiefly of gneiss and granitic slates, and covered with a dense forest growth. In a direct line, it is about fourteen miles from Black Mountain, or "Mount Mitchell," the highest point in the United States east of the Rocky Mountains. It lies between Broad and Catawba Rivers, both of which point to Black Mountain, while on the northwest side of the Blue Ridge, the Swannanoah and Green Rivers, tributaries of the French Broad, have their sources near the Black Mountain. So many large rivers, on both sides of the Blue Ridge, heading up in this section, would indicate Black Mountain as the center of the volcanic force which lifted up these mountain-ridges. I expect to visit these mountains again in July, when I shall have more time to investigate this matter.*"

Extracts from report above referred to, dated Spartanburgh, S. C., March 28, 1874.

On Wednesday, the 18th of March, in company with Rev. R. C. Oliver, editor of The Orphans' Friend, Mr. McKenn Johnstone, civil

* Professor Du Pré has been requested to communicate a report of this projected trip. Further data remain to be gleaned, as the phenomena appear to have continued, at least, up to April.

engineer, and the senior class of Wofford College, I started for Hickory Nut Gap, for the purpose of making such personal observations as my limited time would permit, and of collecting and sifting all the testimony that I could gather from the inhabitants of the affected region. At Rutherfordton, we were joined by Capt. William Twitty, an educated gentleman, who gave us much assistance in our explorations.

To understand the bearing of the facts and testimony upon the question whether these disturbances threaten a volcanic eruption, as a preliminary, I shall describe, as clearly as I can, the situation of this mountain. Five miles east of Hickory Nut Gap, lies this high mountainridge, bearing upon its back several peaks, the highest of which are called Bald, Stone, and Round Mountains, and extending from southwest to northeast, a distance of ten miles, in the order in which they are named. They constitute one mountain-ridge from 3,000 to 3,500 feet high, flanking the Blue Ridge, nearly parallel with it, bounded on the east by Crooked Creek, and on the west by Broad River, which, with its narrow valley, separates them from the high ridge of mountains that border the eastern side of Hickory Nut Gap.

Directing our course along the eastern slope, we came first to the house of Rev. Mr. Logan, a Baptist minister, from whom we learned that the noises and shocks were first heard and felt in Stone Mountain, on Tuesday, the 10th of February; that they were repeated on the following Sunday, with increased severity, so much so that the people sent for him, a distance of ten miles, to hold religious meetings with them; that he and his wife heard the explosions, and felt the shocks repeatedly day and night, once causing the lightning-rods attached to his chimneys. to rattle considerably, the sky being clear, and no wind blowing; that the sounds came from the direction of Stone and Bald Mountains, were at first explosive, followed by a slight rumbling lasting for a few seconds, similar to a blast from a stone-quarry; that the shocks were almost instantaneous with the explosions, very rapid, making the ground tremble for a few seconds. In response to an inquiry, whether any one was blasting rock about the mountains, he replied that none could be found, and there was but one quarry, thirty-three miles distant in an opposite direction, and that had not been worked for several months past.

After going two or three miles further, we turned to the left, and were ascending Fork Knob, over which the road leads to the top of Stone Mountain, when a loud explosion in the direction of Stone Mountain startled us all. It was instantly followed by a low reverberatory sound, as if descending the slope of the mountain. We felt no shocks, which was due, no doubt, to the steep and stony road over which our buggies were passing at the time. This was on the 19th, at 5. p. m. Two of our company who had preceded us a mile, and were about a half mile from the top of Stone Mountain, heard the report, and also felt the ground tremble under them. The sound resembled the suppressed but sudden report of a quarry-blast, and seemed to come through the mount

ain. We arrived about sunset at Mr. Elliott's, whose house is situated in a depression between Round and Stone Peaks, about a half mile from the top of the latter. From Elliott's house, Round Mountain bears north 370 west, Stone Mountain south 73° west, and are about a half or threequarters of a mile distant from each other. This house being about the center of the greatest agitation, and whence most of the exaggerated rumors had their origin, we determined to remain all night, and I kept watch until about two o'clock.

*

*

The next morning I gathered from Mr. and Mrs. Elliott, in answer to many inquiries, the following statement: "The first noise and shakes (as the shocks are very expressively denominated by the mountain people) were heard and felt on Tuesday, 10th February-some of them were felt as far as White House, on Cove Creek, eight miles distant. Sunday morning these sounds and shakes were repeated with increased severity, one a little after sunrise, another at 10, and another at 2 o'clock in the night; noises continued, some with shakes, and some without, until Thursday following, with intervals of about an hour or two. The house-a stout log building-shook so violently that the children became very much alarmed, all thinking it would fall. A ladder resting upon a support in the yard rattled frequently, and the ground seemed to tremble under their feet. The noise began like explosions of a quarryblast, in the northwest, and west off to the southeast, with a rumbling sound under ground. The weather was quite variable, sometimes cloudy and rainy, at other times clear and cool. The people about the mountain were very much alarmed; had preaching and prayer-meetings daily for a week or more, and forty-five new members were added to the Baptist church."

About 9 o'clock in the morning of the 20th we began the exploration of Stone Mountain. From the base to the summit it is covered with a dark rich soil, about a foot deep, partly cleared and cultivated, but mostly clothed with a growth of heavy timber, consisting of chestnut and oak. The granite slates, about the thickness of flag-stones, scattered over the surface, indicate that the formation does not differ from most of the surrounding peaks. Near its highest point several large blocks of coarse granite protrude through the soil to the height of about 10 feet above the surface. Owing to the depth of the soil and the slight exposure of the rocky formations, I could not ascertain the direction or angle of the dip. No specimens were found which resembled what are usually called volcanic rocks. The mountain appeared as calm and peaceful as if it had never been disturbed since the morning of its upheaval. It presented no cavernous depths or rugged prominences to excite the fears of the dwellers upon its slopes. A dozen or more of the mountaineers had followed us everywhere in the exploration, and, although much alarmed at the frequent agitations of this hitherto stable mountain, yet they unanimously contradicted the many rumors of gaping rocks, smoking peaks, sinking caverns, melting snows, &c., with