The volcanic action of the Devonian period was prolonged into Carboniferous times, but was then evidently diminishing gradually in violence. Instead of great central volcanoes, such as existed in the earlier period, we find innumerable small vents which threw out tuffs, agglomerates and lavas, and were scattered over the districts lying around the bases of the now extinct Devonian volcanoes. In the central valley of Scotland and in many parts of England, we find abundant proofs of the existence of these small and scattered volcanic vents during Carboniferous times. The well-known hill of Arthur's Seat, which overlooks the city of Edinburgh, and many castle-crowned crags of the Forth and Clyde valleys, are the worn and denuded relics of these small volcanoes. There are some indications which point to the conclusion that the volcanic action of the Newer Palæozoic epoch had not entirely died out in Permian times, but the evidence upon this point is not altogether clear and satisfactory. During nearly the whole of the Secondary or Mesozoic periods the volcanic forces remained dormant in the area of the British Isles. Some small volcanic outbursts, however, appear to have occurred in Triassic times in Devonshire. But in other areas, such as the Tyrol, South-eastern Europe and Western America, the Triassic, Jurassic, and Cretaceous periods were marked by grand manifestations of volcanic activity. The volcanic forces which had during the long Mesozoic periods deserted our part of the earth's surface, appear to have returned to it in full rigour in the Tertiary epoch. In the Newer-Palæozoic periods the direction of the great volcanic band which traversed our islands appears to have been from north-east to south-west; but in Tertiary times a new set of fissures were opened running from north to south. There is evidence that during the Eocene or Nummulitic period, the first indications of the subterranean forces having gathered strength below the district were afforded by the issue of calcareous and siliceous springs, and soon fissures were opened which emitted scoriæ, tuffs, and lavas. The intensity of the volcanic action gradually increased till it attained its maximum in the Miocene period, when a great chain of volcanic mountains stretched north and south along the line of the Inner Hebrides, the north-east of Ireland, and the sea which separates Great Britain from Ireland. The basal-wrecks of a number of these volcanoes can be traced in the islands of Skye, Mull, Rum, and parts of the adjoining mainland. We have already seen that along this great band of volcanic action, which traverses the Atlantic Ocean from north to south, a number of active vents still exist, though their energy is now far less intense than was the case in former times. The only vestiges of the action of these now declining volcanic forces, at present found in our islands, are the hot springs of Bath and a few