In the year 1828 a great mass of ice was discovered on Mt. Ætna. In consequence of the protracted heat of the season, supplies of ice at Catania and the adjacent regions failed entirely, and the people suffered considerably for the want of an article considered necessary to health as well as comfort in that hot climate. The Catanian authorities caused search to be made for some crevasse or natural grotto on Mt. Ætna, where drift-snow might exist. Near the base of the highest cone was found a vast mass of ice, covered by a lava bed. How old it was there is no means of knowing; nor can we tell how much of the ice might have originally been melted by the overflowing current. But there it was, so hard and firm that the workmen quarried it with great difficulty. Lastly, it appears that the causes of earthquakes and volcanic action must be the same. A violent volcanic outbreak causes earthquake shocks at once, as though relieved by a safety valve. The experiments of Mr. Robert Mallet, the best known authority on earthquake phenomena, tend to prove that the shocks necessarily originate at a comparatively short distance below the surface. So, from two independent lines of investigation, the same conclusion is reached. These objections have caused inquiry to be made as to what causes might locally develop heat. Here there are so many possible methods that scientists may not be expected to unite. One is the chemical theory: water coming in contact with quick-lime, or metallic sodium or potassium, would evolve intense heat. One or two locomotives have been invented which need no fuel, obtaining their heat supply thus. But it is objected to this that the products of volcanic action are not such as would result from such a cause; that all experience indicates that water has already penetrated every portion of the earth, the deepest borings always crossing veins, and all great mines requiring to be artificially drained. One other theory is, that the slow contraction of the globe from the radiation of heat into space necessarily affects the outer portion most directly, and in consequence, the shrinking of the crust at the weakest points produces unusual pressure there, which can evolve intense heat, as is shown by the fact that nearly all rocks so twisted or strained are more or less changed in their internal structure by heat. It is also evident that a region once thus weakened and seriously broken would necessarily form a fairly permanent volcanic tract. As the work of nature all goes to preserve equilibrium or balance of forces, an unusual upheaval would necessitate unusual subsidence near at hand; and in fact the highest mountain is always near the deepest ocean. This explanation, combined with that of chemical action seems to us the more tenable. None of these theories conflict with the nebular hypothesis of Kant and Laplace. In looking over the areas of volcanic action, we will find they have changed considerably from the areas of the past.