THE SWEDISH EARTHQUAKE OF NOVEMBER, 1901. Meddelanden om Jordstötar i Sverige. By E. SVEDMARK. Geologiska Föreningens i Stockholm Förhandlingar, 1902, vol. xxiv., pages 85-120, and 1 map. Vermland is reckoned among those provinces of Sweden wherein earthquakes are of fairly frequent occurrence, and it formed the epicentral area of the earthquake which took place in the night of November 9th to November 10th, 1901. About one second before midnight, two immediately consecutive shocks were felt at Karlstad (the customary centre of the Vermland earthquakes), followed by a rumbling like thunder and by a series of after-shocks. The seismic waves travelled on the whole from north-west to south-east, and the latest and feeblest shock was observed about 2:30 a.m. Having sent out circulars with the usual schedule of questions, the author received replies from 54 localities, and with the help of these he was enabled to plot out the isoseismic curves on the map which accompanies his paper. As above mentioned, Vermland forms the epicentral area, but the outer isoseismic curve extends from Christiania on the east to Upsala and Södertelge on the west, that is, almost as far as Stockholm. The earthquake-sound, by some observers, is said to have culminated in something like a resounding thunderclap or the noise of a shot fired by dynamite. Allusion is also made to a glare or flash of light, which might possibly be due either to an electric discharge or to fluorescence. One does not gather that any damage to persons or property was suffered. In Sweden, these seismic phenomena are in no wise associated with vulcanicity, rather may they be regarded as due to purely tectonic causes, such as sagging or settling along a line of fault, etc. L. L. B. EARTH-TREMORS, ETC., AT ZI-KA-WEI, CHINA. The observatory at the above locality in China is situated not more than Thus in China, just as at Paris and at Lyons, a period of magnetic dis turbance began at a time coincident with the Martinique eruption; and there were also earth-tremors, which appear to have taken about 4 hours to travel from the West Indies to the far east of Asia. L. L. B. VOL. XXIV.-1902-1908. 43 THE PROPAGATION OF EARTHQUAKES. Propagazione dei Terremoti. By GIULIO GRABLOVITZ. Atti della Reale Accademia dei Lincei, 1902, series 5, Rendiconti, vol. xi., pages 177-185. From the complex of records obtained by modern methods of the seismographic registration three principal phases emerge: 1. Rapid undulations which, coming, say, from Japan, reach Italy about hour after the commencement of the earthquake at the epicentrum, and are protracted for several minutes. 2. Slackened undulations, of greater amplitude than the foregoing, arriv ing 10 minutes later, or 25 minutes after the commencement at the epicentrum. 3. Slow oscillations of 15 seconds period, 30 minutes after the first phase, or 45 minutes after the commencement at the epicentrum. These oscillations generally attain their greatest amplitude 5 or 10 minutes after their first arrival, and they are preceded by extremely slow oscillations (of 60 seconds period), of inconsiderable amplitude and revealed alone by specially delicate instruments. This third phase occasionally lasts for a few hours, and the instruments available are hardly sensitive enough to determine the precise moment at which it ceases. The author points out that the hypothesis of longitudinal and transverse oscillations, lately received with much favour, takes into account the first and the third phases, but leaves unsolved the problems attaching to the second phase. The intervals between the three phases and their duration increase concurrently with the distance from the epicentrum; and the author explains on what grounds he established his formerly suggested co-efficient of 186 miles (300 kilometres) for every minute's interval between the beginning of the first and that of the third phase. He now shows to what modifications this co-efficient is subject, in view of improved methods of seismographic registration, discussing for this purpose the results obtained by Messrs. Milne, Oldham and Belar. The varying velocity of the first phase causes the co-efficient to vary according to the distances, but the tabulated results show that the range of variation is, after all, not so very great, and the rough estimate of 300 was nearer the truth than might have been expected. In the analysis of earthquakes over an area where the general public has been conscious of their occurrence, the distances dealt with rarely exceed 620 miles (1,000 kilometres). Moreover, at most points of observation, it is not the actual first oscillation that is recorded, but a more advanced phase, and even in recording this there is some delay. Then, although it is usual in dealing with remote earthquakes to regard the co-efficients of velocity as constant, we should bear in mind the modifications which they may undergo over short distances, in consequence of the predominance of strata more or less favourable to rapid seismic propagation. The third phase itself, of the ascertained velocity of 2 miles (3 kilometres) per second in the epicentral area, is more distinctly felt, and actually overhauls " the others. The depth of the epicentrum, largely negligible over great distances, is a factor of considerable importance over short distances. The author concludes, therefore, that very precise observations, made with the very best instruments, are necessary, in order to deduce those laws which one may vainly attempt to build on incomplete and inexact narrations. 66 L. L. B. FOLDING OF ROCKS IN RELATION TO EARTHQUAKES. Sur l'Influence Sismique des Plissements armoricains dans le Nord-ouest de la The author, a well-known seismologist, states that the object of this paper is to show in what measure the instability of the earth's crust is traceable to those post-Carboniferous, so-called Armorican, folds, which characterize the region now occupied by the south-west of Ireland, the northern shores of the Bristol Channel, Cornwall, and the French Palæozoic massif (Britanny, the Cotentin, and Vendée). Seismic epicentra are disseminated all over this area, but attention is directed to the manner in which those that are most frequently the locus of earthquakes are grouped together. Isolated and infrequently active epicentra may be generally traced, with a considerable show of reason, to some local geological "accident" or fault-line. Epicentres may be traced along the Armorican folds in county Cork, and across into south-western Pembrokeshire (Haverfordwest, etc.), and thence right into the Mendips. The great fold disappears at Frome beneath the Mesozoic formations, but it is evidently continuous at some depth below the South Downs, reappearing in France, where its course is marked by seismic epicentra through the Boulonnais and into Belgium. In the same way a connection is traced between the Armorican folds and the seismic epicentra, from Dartmoor to the Scilly Isles and across to Britanny and in the Channel Islands. Metalliferous injections appear to have had no seismic influence in Cornwall, but the same assertion cannot be made in regard to the elvans. Nor do granitic intrusions, whether in Cornwall, or in southwestern Ireland or in Vendée or Britanny, coincide with any important seismic epicentra. The geological phenomena which resulted in the breaching of the formerly continuous land-line by the Irish Sea and the English Channel had no influence in determining the seismic instability of the area, any more than the late Tertiary elevations and subsidences. Similar observations hold good concerning many regions of the globe's surface, for such phenomena as these are too superficial, while the origin of the great folds may be very deep-lying. "To sum up-the Armorican folds, despite their great antiquity, have retained a remnant of vitality, in the shape of fairly frequent, not very intense earth-tremors, with numerous epicentra." The older Caledonian folds, with which the Armorican folds are associated along the northern shore of the Bristol Channel, constitute, on the other hand, an element of stability. L. L. B. THE FOLD-THEORY OF EARTHQUAKES. Les Tremblements de Terre de Plissement dans l'Erzgebirge. By F. DE MONTESSUS In the region, which is bounded by the Frankenwald on the west, the Eger on the south, and the Elbsandstein on the east, earthquakes without being, as a rule, of disastrous intensity, are of frequent occurrence. Geologists are generally agreed that the physiographical structure of the region is in great part the outcome of a triple folding, begun in Archæan times and continued during subsequent periods; this folding took place from south-east to P north-west, and thus arose three sensibly parallel ranges trending from southwest to north-east:-The Mittelgebirge being the southernmost, the Erzgebirge lying north of it, and the Liebschütz Hills north of that again. The Erzgebirge, the most elevated and longest fold of the three, slopes on the one hand down to the peneplain of Saxony, and on the other abuts as a great wall on the Eger Valley and the Bohemian volcanic fault. This fault-line is marked by many thermal springs, among which those of Franzensbad and Teplitz are the most renowned. The whole area has been injected with granitic and other laccolites, and complicated with basaltic flows. Metalliferous veins of various composition and age course in every direction through the rocks. In the troughs of the folds lie the more or less eroded sedimentary deposits. The instability of the region is manifested by the number of epicentres, 150 or more, scattered all over it, but perhaps more closely clustereed together in the south-west of the Erzgebirge than elsewhere, and Graslitz and Brambach may be regarded as the districts of greatest seismicity. Now, the GraslitzBrambach epicentres are evidently connected with certain huge quartz-reefs which fill up long fractures running at right-angles to the Erzgebirge range, and in some cases crossing even the Eger valley. Owing to this and other circumstances, the author infers that the folding movement begun in the dim recesses of Archæan time is still going on, and the recent earthquakes are its attenuated manifestations. On the other hand, the innumerable fractures that characterize the Vogtland and Saxony have, on the whole, given rise to only a small number of epicentres. It is as if the quartz-infilling had cemented that area into a gigantic breccia, and thereby made it more stable than otherwise. Here then faulting has an exactly opposite effect, so far as seismicity is concerned, to folding a conclusion which is confirmed on examining the circumstances connected with the great Bohemian volcanic fault. Saxon Switzerland, despite its rugged configuration, is a very stable area. A few unimportant epicentres along the right bank of the Elbe, are connected with the great dislocation of the Lausitzerwald granite. The author points out, however, that it would be very rash to connect every seismic epicentre with some neighbouring geological dislocation or such like phenomenon. Still less is it advisable, as many seismologists have done, in the absence of visible geological disturbances, to regard earthquakes as the outward manifestation of unknown subterranean faults. To sum up, in the Erzgebirge, out of three kinds of geological phenomena implying at least temporary instability (fracture-areas, volcanic "lines of least resistance," and folds) the last-named alone has remained a living force down to our own days, manifesting itself by means of earthquakes. L. L. B. THE RELATIONSHIP OF SOUND-PHENOMENA TO EARTHQUAKES, Über die Beziehungen zwischen Erdbeben und Detonationen; and Bericht über das Detonationsphänomen im Duppauer Gebirge am 14. August, 1899. By J. KNETT. Sitzungsberichte der Mathematisch-naturwissenschaftlichen Classe der kaiserlichen Akademie der Wissenschaften [Vienna], 1900, rol. cir., abtheilung I., pages 700-734, with 3 figures in the text, and pages 735-767, with 6 figures in the text and 2 plates. Pointing out in the first place the general consensus of experience that the sound which accompanies an earthquake is directly proportional in in tensity to the violence of the shock, the author draws attention to certain cases wherein the terrific loudness of the sound-phenomena has, however, been out of all proportion to the comparatively feeble vibration of the soil. To seek for the cause of these it seems needful to start from the premiss that certain "earthquake-sounds" or detonations are independent phenomena, the result of one or more causes originating in a particular focus, and the earth-tremors observed in connexion with them are merely accessory accompaniments originating in the same focus. Feeble detonations are unaccompanied by any observable earth-tremors. Among such the author reckons the Barrisal guns of Java, the Gangetic plain, and the Congo, the Marina" of the Umbrian coast, and the Mistpoffers" or "Zeepoffers" of the Flemish coast. These phenomena, feeble though they be, are remarkable for their continual recurrence at the same localities, and it may be remembered that Prof. George Darwin has assigned them to microseismic movements of the earth's crust. Of another order are the detonation-swarms," consisting of a more or less rapid succession of thunderous sounds, in a region where they have not occurred before and do not recur so far as we know. Such swarms may go on for weeks, months, or even years at a time. Such were those of Guanaxuato (Mexico) lasting from January 9th to February 14th, 1784: of Villaga, Italy, from November 4th to December 26th, 1851; of Meleda, Dalmatia, lasting from 1822 to 1825. After a short description of these, the author proceeds to discuss minutely the relation between tremor and detonation, and seeks to prove that in a given medium both travel with an equal velocity-in a word, that the seismic and acoustic waves transmitted by ponderable matter have much the same mutual relationship as the electromagnetic and optical waves transmitted by imponderable matter. This equality of velocities in the purely seismic phenomena of the lithosphere applies only to the rapid [transverse] vibration-waves. What the author terms "not purely seismic, or mixed" phenomena of the lithosphere, such as tremors connected with certain volcanic eruptions, give rise to acoustic waves which, however, are propagated with the slow [longitudinal] earthHe enunciates his "detonation-theory" as follows:-Earth-sounds are for the most part mixed phenomena of predominantly acoustic origin. These are propagated from their focus through the earth's crust by means of waves which correspond to the earthquake-waves proper (slow waves), and possess the same velocity as the last-nained. The "report" of such detonations bears no analogy to the noises heard before the principal shock in most earthquakes. The detonations are of various intensities, and are, as a rule, accompanied by vibrations of the surface of the environing medium, the intensity of such vibrations being generally concordant with that of report." waves. the Detonations are classified by the author, according to their degree of intensity, in five categories, and he emphasizes by description and diagram the distinction between these phenomena and earth-tremors. He then endeavours to trace out the possible causes of the phenomena, and refers in this connexion to sudden outbursts of gas below ground and to the sudden caving-in of subterranean caverns, etc. In his second memoir, he describes the detonation-phenomena observed around Duppau in Bohemia on August 14th, 1899, between 6 and 6.15 p.m. These consisted of a couple of subterranean "thunderclaps" of medium intensity (3 in the author's scale), accompanied by a feeble earth-tremor (2 to |