The ages that elapsed between the final dying out of the Palæozoic volcanoes and the outburst of those of Tertiary time were so protracted that many revolutions of the geography of Europe were comprised within them. Land and sea changed places again and again. First came the singular topography of the Trias, which prolonged and accentuated the characteristics of the closing Palæozoic ages. Next arose the more genial climate and more varied geography of the Jurassic period, when comparatively shallow seas overspread the site of most of the European continent, and tracts of old land stretched away to the west and north. Another crowded succession of changes in the disposition of land and sea filled the long Cretaceous period, at the close of which a more rapid and complete transformation in European geography took place. Yet during all these transitions and vicissitudes, so far as we know, volcanic energy remained quiescent throughout Western Europe. It was not until some time after the great terrestrial movements that raised so much of the Cretaceous sea-floor into land, and laid the foundations of the modern continent, that the subterranean fires once more awoke to vigorous action. The renewal of eruptions in the early ages of Tertiary time was as widespread as it was energetic. Over many regions of the European continent volcanoes broke out either in new areas or on old sites. For the most part they appeared as scattered puys or as Vesuvian vents, generally not of the first magnitude, like those of Central France, Hungary, Würtemberg and Italy. But in the north-west they assumed more colossal proportions, and took the form of fissure-eruptions by which many thousands of square miles of country were deluged with lava. From the South of Antrim all along the West of Scotland to the north of the Inner Hebrides remains of these basalt-floods form striking features in the existing scenery. The same kind of rocks reappear in the Faroe Islands and in Iceland, so that an enormous tract of North-western Europe, much of it now submerged under the sea, was the scene of activity of the Tertiary volcanoes. In entering, therefore, upon a consideration of the British Tertiary volcanic rocks, we are brought face to face with the records of the most stupendous succession of volcanic phenomena in the whole geological history of Europe. Fortunately these records have been fully preserved in the British Isles, so that ample materials remain there for the elucidation of this last and most marvellous of all the volcanic epochs in the evolution of the continent.