Trof, J. W. Judd — On Volcanos, 531 



disturbance, commencing in the Oligocene period, and thence gradu- 

 ally augmenting in violence, attained its climax towards the close of 

 the Miocene, and then as gradually died away during the Pliocene 

 post- Pliocene, and recent periods; the movements on the southern 

 flanks of the axis being more prolonged than on its northern side. 



And it is a most interesting circumstance that a very striking rela- 

 tion can be shown to exist between these movements in the great 

 mountain axis itself and the activity of the volcanic belt which 

 stretches on either side of it. The volcanic outbursts which, as we 

 have seen, commenced in the Oligocene period, acquired continually 

 new strength and vigour, till at the close of the Miocene they had 

 built up a series of volcanic cones, rivalling Etna in their proportions 

 and forming almost continuous chains stretching on both sides of 

 and parallel to the great mountain axis ; but, from that period down 

 to the present, the volcanic activity has been in a state of continual 

 but gradual decline, the vast cones falling into ruin, and the dying 

 subterranean energies sufficing to produce only long lines of splutter- 

 ing "puys;" till finally geysers and mud-volcanos, hot-springs and 

 gaseous exhalations, testify to their having reached the stages of ex- 

 haustion, senility and utter decay. Yet this decline certainly took 

 place faster on the northern side of the axis — where not a single active 

 vent at present remains — than on its southern side — where Etna 

 and Santorin, Vesuvius, Stromboli, and Volcano retain something of 

 the fires of their youth; and where not a few outbursts during the 

 historical period in the same Mediterranean area have served to 

 remind us that forces as yet unspent still have their habitation 

 beneath it. 



We have already spoken of the evidences of the gradual appear- 

 ance and growth in energy of the volcanic forces on both sides of 

 the Alpine system during the Oligocene period. We will now 

 briefly sketch, so far as the materials at our disposal enable us to do 

 so, the actual condition of the volcanic centres which surrounded 

 the Alpine system at the period of their maximum violence, towards 

 the close of the Miocene period. 



Among the most interesting of the facts established during the 

 voyage of the " Challenger " is that of the existence of a great sub- 

 merged ridge stretching from north to south through the Atlantic. 

 The few peaks of this ridge, which rise from depths of 25,000 feet, 

 and now reach the sea-level, there forming groups of islands, are 

 almost all volcanic, though usually either extinct or exhibiting 

 evidences of various stages of decadence. It is hardly possible to 

 doubt that the' subsidence and submergence of this vast ridge is 

 connected with the gradual decline of volcanic energy beneath it. 

 The evidence obtained in Greenland, the Hebrides, Madeira, and the 

 Azores, all points to the inference that the period of maximum 

 activity in this volcanic band was the Upper Miocene ; and certain 

 facts in our own islands suggest the conclusion that the commence- 

 ment of volcanic action in it must be referred to a somewhat earlier 

 portion of the Tertiary period. Hence it is not difiicult to picture 

 to ourselves the existence in later Tertiary times of a great band of 



