ANNIVERSARY ADDRESS OF THE PRESIDENT. I7I 



M"hich I have enumerated contemporaneous igneous rocks repeatedly 

 occur, and in some of them on such a scale as to indicate prolonged 

 and vigorous activity. 



One conspicuous feature, however, in this long volcanic history is 

 the entire absence of any evidence of eruptions during the whole of 

 the Mesozoic periods. In this respect Britain only illustrates the 

 general quiescence of volcanic energy over the European continent 

 during that vast interval of geological time.^ 



3. Not only has there been a remarkable persistence of volcanic 

 activity over the comparatively limited area of the British Isles, 

 viewed as a whole, but if we examine the different parts of this 

 area we perceive that many of them, of relatively restricted extent, 

 have been the sites of a recrudescence of volcanic action again and 

 again through a succession of geological periods. While the whole 

 region has been in different quarters and at different times affected, 

 there have been districts where the volcanic fires have been rekindled 

 after long intervals of quiescence, the new vents being opened 

 among or near to the sites of earlier volcanoes. In the south-west 

 of England, for example, the tuffs and agglomerates of Cornwall 

 (Meneage), probably of Oaradoc age, were followed in Middle 

 Devonian time by the outpouring of the Ashprington tuffs and 

 diabases ; these were succeeded in the Carboniferous period by the 

 eruptions of the Culm Measures, and in the very same tracts came 

 last of all the lavas and tuffs of the Permian conglomerates. Still 

 more astonishing is the record of volcanic energy in the south of 

 Scotland, where, within a space of not many hundred square miles, 

 there are the chronicles of the Llandeilo eruptions of the Southern 

 Uplands, the huge piles of porphyrites and tuffs of the Lower Old 

 Red Sandstone, the long succession first of the plateaux and then 

 of the puys of the Carboniferous period, the groups of tuff cones of 

 the Permian period, and, lastly, the numerous dykes connected with 

 the Tertiary volcanoes. 



In this connexion it is well to notice that, besides areas specially 

 liable to exhibitions of volcanic action, there have lain near to or 

 among these areas others that seem to have remained continuously 

 unaffected. Besides the non-volcanic eastern tract, already noticed, 

 the Central Highlands of Scotland appear to have been exempt from 

 volcanic eruption since the time of the metamorphism of their schists. 

 In the wide spread of the Carboniferous rocks over the greater part 



' The Triassic eruptions of the Continent were important, and traces of 

 others are said to occur in the Cretaceous system in Portugal and Silesia. 



