In no department of science is the slow and chequered progress of investigation more conspicuous than in that branch of Geology which treats of volcanoes. Although from the earliest dawn of history, men had been familiar with the stupendous events of volcanic eruptions, they were singularly slow in recognizing these phenomena as definite and important parts of the natural history of the earth. Even within the present century, the dominant geological school in Europe taught that volcanoes were mere accidents, due to the combustion of subterranean beds of coal casually set on fire by lightning, or by the decomposition of pyrites. Burning mountains, as they were called, were believed to be only local and fortuitous appearances, depending on the position of the coal-fields, and having no essential connection with the internal structure and past condition of our planet. So long as such fantastic conceptions prevailed, it was impossible that any solid progress could be made in this branch of science. A juster appreciation of the nature of the earth's interior was needed before men could recognize that volcanic action had once been vigorous and prolonged in many countries, where no remains of volcanoes can now be seen. To France, which has led the way in so many departments of human inquiry, belongs the merit of having laid the foundations of the systematic study of ancient volcanoes. Her groups of Puys furnished the earliest inspiration in this subject, and have ever since been classic ground to which the geological pilgrim has made his way from all parts of the world. As far back as the year 1752, Guettard recognised that these marvellous hills were volcanic cones that had poured forth streams of lava. But it was reserved for Desmarest twelve years later to examine the question in detail, and to establish the investigation of former volcanic action upon a broad and firm basis of careful observation and sagacious inference. His method of research was as well conceived as the region of Auvergne was admirably fitted to be the field of exploration. He soon discovered that the volcanoes of Central France were not all of one age, but had made their appearance in a long series, whereof the individual members became less perfect and distinct in proportion to their antiquity. Beginning with the cones, craters, and lava-streams which stand out so fresh that they might almost be supposed to have been erupted only a few generations ago, Desmarest traced the volcanic series backward in time, through successive stages of the decay and degradation wrought upon them by the influence of the atmosphere, rain and running water. He was thus able, as it were, to watch the gradual obliteration of the cones, the removal of the ashes and scoriæ, and the erosion of the lava-streams, until he could point to mere isolated remnants of lava, perched upon the hills, and overlooking the valleys which had been excavated through them.