Similarly the extinct volcanos of Europe may be grouped very conveniently in a few systems of connected groups. The basaltic mountains and cliffs of the Farö Isles are stated to be on many points allied to those of Staffa and Antrim, and perhaps the whole region in which igneous rocks are scattered, from the Farö Isles to Antrim, Arran, the Vales of Clyde and Forth, if not to Teesdale and Derbyshire, should be viewed as the theatre of one great and long enduring system of submarine volcanic forces.
Another great system, of more recent date, is the tripartite volcanic tract of Central France, included in the districts of Auvergne, Cantal, Velai, and Vivarais, to which we may attach some points scattered about the Cevennes mountains near Rodez, at Agde near Montpellier, and Beaulieu, near Aix en Provence.
Just before the Rhine enters the Low Countries, which conduct it to the sea, it divides hilly districts, principally of transition rocks, among which, on the left bank, is a large exhibition of ancient volcanic energy, in the numerous cones and "maars" of the Eifel country, lying east of the Ardennes. On the right bank, lower down, are the celebrated trachytic and basaltic mountains, called the Siebengebirge, which by some detached rocks of like nature, lying to the east, appear to be connected with the great basaltic masses of the Westerwald.
The Westerwald, Vogelsgebirge, and Rhongebirge, may be taken as the principal volcanic group of Western Germany. Many insulated cones and masses of basaltic rocks about Limberg and Wetzlar, the Habichtwald near Cassel, some basaltic hills near Eisenach, Fulda, Hanau, and Frankfort, may perhaps be contemplated as parts of this ancient system.
The Kaiserstuhl mountain, near Freyburg in the Brisgau, the cone of Hohentwiel, and some small points in Würtemberg may be grouped together, though it is not known that they have really any particular geological relations.
