_Conclusion._—Although it would be an easy matter to discuss the relationship of earthquakes and other phenomena, we must conclude that the primary cause of earthquakes is endogenous to our earth, and that exogenous phenomena, like the attraction of the sun and moon and barometric fluctuations, play but a small part in the actual production of these phenomena, their greatest effect being to cause a slight preponderance in the number of earthquakes at particular seasons. They may, therefore, sometimes be regarded as final causes. The majority of earthquakes are due to explosive efforts at volcanic foci. The greater number of these explosions take place beneath the sea, and are probably due to the admission of water through fissures to the heated rocks beneath. A smaller number of earthquakes originate at actual volcanoes. Some earthquakes are produced by the sudden fracture of rocky strata or the production of faults. This may be attributable to stresses brought about by elevatory pressure. Lastly, we have earthquakes due to the collapse of underground excavations. CHAPTER XVIII. PREDICTION OF EARTHQUAKES. General nature of predictions—Prediction by the observation of unusual phenomena (alteration in the appearance and taste of springs; underground noises; preliminary tremors; earthquake prophets—warnings furnished by animals, &c.)—Earthquake warning. _General nature of predictions._—Ever since seismology has been studied, one of the chief aims of its students has been to discover some means which would enable them to foretell the coming of an earthquake, and the attempts which have been made by workers in various countries to correlate these occurrences with other well-marked phenomena may be regarded as attempts in this direction. Ability to herald the approach of these calamities would unquestionably be an inestimable boon to all who dwell in earthquake-shaken countries, and the attempts which have been made both here and in other places are extremely praiseworthy. In almost all countries where earthquakes are of common occurrence these movements of the earth have been more or less connected with certain phenomena which, in the popular mind, are supposed to be associated with an approach of an earthquake. If predictions were given in general terms, and they only referred to time, inasmuch as on the average there are in the world several shakings per day, we should always find that predictions were verified. We might even go further and predict that on certain days earthquakes would occur in certain countries, and still find that in many instances our supposed power of foresight had not deceived us. Thus, for instance, in Japan, where on the average there are probably one or two shakings every day, if prognostications were never correct there would be a violation of the laws of chance.