OF VOLCANIC ROCKS. 91 



occur. The Alps and the Himalaya are the most striking instances of this kind. The 

 first of these, and probably, too, the other, had, as we mentioned before, undergone a 

 considerable elevation in and after the porphyritic era, but have probably changed their 

 altitude very little in the next following periods. The acceleration of their elevation 

 during the volcanic era appears, however, to have greatly exceeded that of the Andes. 

 The coincidence in time of these events, and of all the phenomena characteristic of the 

 volcanic era, justifies the supposition that they are connected in their origin. 



If we contemplate, in its relations to the volcanic era, the great elevated belt of 

 which the Alps and Himalaya form the axis, we find it to consist of three parallel 

 zones. The central one comprises those two mountain ranges and the broad moun- 

 tainous country which connects them, and which owes its configuration chiefly to the 

 events of the volcanic era. The Alps and Himalaya are free from volcanic rocks. This 

 is also true as regards the central portions of those chains which branch off from the 

 Alps in a southeasterly direction, and of those (as far as their geology has been ex- 

 plored) which extend westerly from the Himalaya. The farther one proceeds in the 

 Turkish peninsula towards the east, the more frequent are the monuments of eruptive 

 activity of the volcanic era; they are known in Servia and Bulgaria, in the north, and 

 in Macedonia, Thracia and Bpirus, in the south. They increase in similar ratio as 

 one proceeds westerly from the Himalaya, through the highlands of Armenia to Asia 

 Minor. If it is considered that active volcanoes are particularly numerous in those 

 regions where the elongated portions of two different continents have, as it were, a 

 tendency to connection, the analogy with the mode of distribution of volcanic rocks 

 in the regions mentioned is conspicuous. The system of the Alps with its southeastern, 

 and that of the Himalaya with its western branches, were disconnected before the Ter- 

 tiary period, and were united into one mountainous belt during the same. The eruptive 

 activity contemporaneous with this slow process was remote from the main axis where 

 this had existed as an elevated range before, and approached it more and more, from 

 both sides, increasing, at the same time, in intensity, until it culminated in that 

 region where the connection of both systems was effected. Massive eruptions and 

 volcanic activity have ceased completely in this central zone. 



North of this, is another zone, which was distinguished in its entire length by 

 the intensity of eruptive action in the volcanic era. It stretches from Central Asia by 

 the Caspian Sea, the Caucasus, the Crimea, the Carpathians and, in branches, through 

 central Germany to central France. In the European portion of this zone, there are 

 only recognizable in thermal and mineral springs the last feeble remnants of former 

 volcanic activity, while they are somewhat more energetic in that portion which is 

 situated on the Asiatic continent. A third zone, not less distinguished for the in- 

 tensity of eruptive action in the volcanic era, accompanies the main axis to the south. 

 It traverses India, and, in the Bay of Bengal, is connected with the volcanic belts of the 

 Indian Archipelago, while it continues to the west through Arabia, Syria, Palestine, to 

 the Mediterranean, where it comprises the active volcanoes of the Grecian Archipelago 

 and Italy, and is connected by Sardinia and southern Spain with the Azores. Volcanic 

 activity still continues in this belt, but the period of the massive eruptions has passed 

 long ago. 



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