The screw H is attached to the part D by means of a revolving joint, and it works in the nut at C, so that, on being turned, it alters the inclination of the part D to the fixed part A. The part I, which contains the outer axis of the theodolite, has an axis (like E) working in the sockets F F. The screw K, working in the nut at G, and being attached to the part I by a revolving joint, alters the inclination of I with regard to D; so that, by means of the two screws H and K, the part I can be inclined in any manner to the fixed part A, while there is in every portion of the apparatus a firm resistance to a motion in azimuth. The small screw L is intended to temper the pressure of a piece of tin, inserted into the nut to make up for the wearing of the levelling screw. This apparatus will add to the expense of a theodolite, but by no means in proportion to the time which it will save. JOHN SANG. KIRKCALDY, 4th Nov. 1843. Observations on the Motion of Earthquakes transmitted under the Andes. By RICHARD SOLLY, Esq. Communicated by the Author. Sir,-Having been lately engaged on a paper for the Sheffield Literary and Philosophical Society, the subject of which was earthquakes, I have been much interested in the valuable communications published in your Journal, especially those of Professor Bischof, Dr Daubeny and Mr Milne. One or two remarks have occurred to me respecting a fact which I have not seen alluded to by any of our geologists, but which you may perhaps consider as not altogether unworthy of their attention. I refer to the shocks of earthquakes having extended beyond vast mountain ranges, and yet having been felt either very slightly, or not at all, in those mountains. Mrs Maria Graham, in her account of the great earthquake of the 19th November 1822,* which destroyed so many build * Trans. Geol. Soc. 2d series, vol. i. part ii. p. 413. ings in the town of Valparaiso, and permanently raised the adjoining coast from two to three feet, states that it was felt eastward, beyond the Andes, at Mendoza and St Juan. I heard the same account when I was in Chili in 1828, and have no doubt whatever of the fact. I crossed the Andes that year by the Aconcagua and Uspallata Pass, six years therefore after the great earthquake, and my astonishment was excited by the position of an immense mass of rock called the "Penon rajado," or "Piedra partida," about half way between the Cumbre and the Plain of Uspallata, and 7300 feet above the level of the sea. It had evidently fallen, at some former period, from the cliffs above, and had split into two large pieces and several smaller. The equilibrium of both of the principal fragments appeared so precarious that in spite of the burning sun, one of my companions refused to repose under their shade, being convinced, as he said, “that the slightest shock would overthrow the enormous mass and crush us to atoms. This seemed likely enough, but nevertheless our head muleteer, Pedro Aransivia, assured us that they had not changed their position in his time, nor in that of his father before him, and that they had always availed themselves of their shelter; also, that there were traditions, respecting the ancient Incas, connected with these rocks. A Of the great Conception earthquake of the 20th February 1835, which permanently raised the coast two feet and upwards, Captain Fitzroy says, "This earthquake was felt at all places between Juan Fernandez and Mendoza. At Mendoza the motion was evenly gentle. Towns and houses which lay between the parallels of 35 and 38, suffered extremely, nearly all were ruined, but northward and southward of those latitudes slight injury was done to any building."+ This account I know to be correct, with the exception of the first sentence, if taken literally, as the shock was not felt in the Andes, although it was felt beyond them, at Mendoza. An intimate friend of mine happened to be in the Cordillera at the time, and I can state positively that neither he nor any of his party * Extract from my journal, written at the time. + Narrative of the surveying voyages of the Beagle, vol. ii. p. 418. knew that there had been an earthquake until their arrival at Mendoza. These facts are quite in harmony with the theory adopted by Professor Bischof, by Mr Darwin and other eminent geologists, at least partially, which Professor Phillips favours,* and which Mr Lyell requires,† namely, that the nucleus of the earth is an intensely heated liquid or fluid mass. This granted, motion is supposed to be transmitted by subterraneous undulations to enormous distances, proportionate to the strength of the explosion, and the depth beneath the earth's surface at which it takes place. Now, we can well imagine that an immense mass of mountains, such as the Chilian Andes, ‡ might ride unshaken (while lower ground suffered) like a ship of the line which moves not with the ripple tossing the little boat at its side. Nevertheless we know that the Andes do sometimes suffer extreme dislocations; for instance, by the Tacna shock of the 18th September 1833, of which Mr Matthie Hamilton gives a circumstantial account in your Journal.§ He states that after the calamity, when the atmosphere became clear, the Andes, as seen from Tacna, presented a novel spectacle, and in many parts appeared with a new surface, large portions had been thrown off, or had slid into vaileys below, leaving some of the more elevated peaks denuded of what had been their more prominent limbs; and he gives many other similar particulars. Indeed the examples of shattered mountains are too numerous to require citing. Mr Darwin expresses his surprise at the effect produced by the Conception earthquake of 1835, on the island of Quiriquina. He says, "The effect of the vibration on the hard primary slate which composes the foundation of the island. was still more curious, the superficial parts of some narrow ridges were as completely shivered as if they had been blasted by gunpowder."|| * Treatise on Geology, vol. ii. p. 209. † Elements of Geology, p. 267. From 11,000 to 23,000 feet high and from 100 to 200 miles across. § Jameson's Philosophical Journal, vol. xxx. p. 153. Journal of Researches, p. 370. May we not then assume as correct, both explanations of the mode in which earthquakes are supposed to transmit their motions? by the undulations of the subterranean fluids, and by the vibrations of the superficial crust. Mr Milne has pointed out that most of the English and Scotch earthquakes, being confined to mere patches of the earth's surface, must be due to the latter; and, on the other hand, Professor Phillips remarks that rocks being very imperfectly elastic, owing to the numerous divisions which intersect them, cannot be supposed capable of transmitting vibrations to any very considerable distance. To the subterraneous undulation we may attribute the motion; which passing under, without shaking the Andes, was felt "evenly gentle" at Mendoza. To the superficial vibration we may attribute the fall of the mountain peaks at Tacna, the shivered rocks at Quiriquina, and those strange rotatory motions referred to by Mr Darwin,* and of which I have seen striking examples at Tacna and at Lima. In the latter case the upper stone of a lofty obelisk was turned, in 1828, in a manner precisely similar to that in Calabria, of which Mr Lyell has given a drawing.† The question occurred to me some time since, though I should scarcely have ventured to mention it without having seen Professor Keilhau's remarks in your last number, whether frequent vibration, repeated during long series of ages (which, according to Mr Darwin, I will suppose to accompany the elevation of a mountain chain), may not have produced considerable changes, all tending to crystalline forms, in the molecular constitution of some of the basaltic and metamorphic rocks. It is now an ascertained fact, though but recently acknowledged, that malleable iron, and other metals in a fibrous state, assume the crystalline, under the operation of vibration, and without the accession of heat.§ My friend Mr William Lucas, (this year the President of our Sheffield So * Journal of Researches, p. 376. † Principles of Geology, 6th edit., vol. ii. p. 336. Journal of Researches, p. 380; and Geological Observations on Volcanic Islands, pp. 95 and 129. The axle-trees of railway carriages, and the holding down pins in iron works, afford familiar instances. ciety) has been making some interesting experiments on the changes in metals, and I have requested him to extend them to rocks, which I hope he will do. SANDON PLACE, SHEFFIELD, 28th May 1844. RICHARD SOLLY. On Parietin, a Yellow Colouring Matter, and on the Inorganic By ROBERT D. THOMSON, M.D. Com Food of Lichens. municated by the Author.* The objects of the present paper are, 1st, To endeavour to prove that, contrary to the usually received opinion, the class of plants termed Lichens, require inorganic matter as part of their food, which they must derive from the localities upon which they are fixed; and, 2d, To describe the yellow colouring matter obtained from the yellow wall lichen, and to detail its properties, composition, and application, as a test for alkalies. Although chemists are acquainted with several yellow colouring matters, few of them have been separated in a pure state, and analysed. This arises from the difficulty of procuring such substances in the same state as that in which they existed in the plant from which they are extracteddepending principally on the facility with which they unite with oxygen, and on their consequent conversion into a body of inferior beauty, and of an uncrystallized structure. The yellow colouring matters which have hitherto been analysed, are derived from various parts of phenogamous plants, principally the roots and flowers. The subject of the present paper is procured from a totally different tribe-the lichensbut one to which we are indebted for some important dyes. The Greeks gave the name λ to a disease of the skin, and likewise to certain plants possessing the power of healing these cutaneous eruptions. Dioscorides † tells us that the lichen, which is familiarly known from its growing on stones, and attaching itself to the rough parts of rocks, like a moss, was * From the Transactions of the Glasgow Philosophical Society. † Mat. Med. b. iv. cap. 48. |