THE NATURAL HISTORY OF IGNEOUS ROCKS. 19 



western portion of Italy westward, so as to include part of 

 the African coast and the Cabo de Gata district in Spain ; 

 Hungary and Transylvania ; Servia and Rhodope ; and the 

 JE^e.ah, continuous towards the east with part of Asia 

 Minor. Each of these areas is embraced by mountain- 

 chains belonging to the Alpine system, and they occupy 

 indeed the spaces left between the several branches where 

 least compressed. Another group of provinces, in some 

 cases less sharply defined, occurs just outside the northern 

 border of the main belt of folding. To this belong 

 Auvergne and Cantal ; the Eifel and the Siebengebirge ; 

 Hesse, the Vogelsgebirge, and the Rhon ; the Saxon 

 Mittelgebirge, and Bohemia. Within the areas thus 

 defined are districts containing volcanoes which have not 

 long been extinct, while in the former group of provinces, 

 viz., in the lobes of the Mediterranean embraced by moun- 

 tain-chains of the Alpine system, vulcanicity is still active 

 at several centres. 



It will be observed that the foregoing summary of the 

 distribution of Tertiary and post-Tertiary igneous activity 

 in this quarter of the globe is incomplete, in that it makes 

 no mention of the British Islands. Antrim and the Inner 

 Hebrides, with their Eocene igneous rocks, form part of a 

 great province extending northwards into the Arctic regions, 

 within which vulcanicity has been operative in Tertiary 

 times, and in some districts has not yet died out. Further, 

 this Brito- Icelandic province is itself only part of a region 

 which also includes the Azores, Canaries, Cape Verd Islands, 

 Ascension, St. Helena, and Tristan d'Acunha, with parts of 

 the Portuguese and African coasts, thus stretching along the 

 whole Atlantic border of the Old World. Unlike the others 

 already noticed this region has a general meridional trend. 

 Bertrand sees in this extra- Alpine region of Tertiary igneous 

 rocks the illustration of a new principle, the operation of 

 which is not to be seen, or at least is not clearly marked, in 

 the earlier geological periods. The igneous rocks are still 

 related to crust-movements, but in this case to those greater 

 movements of which oceanic depressions and continental 

 elevations are the results. We have indeed scattered relics 



