CHAPTER XXXI.

ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS--_continued_.

Volcanic rocks of the Older Pliocene period--Tuscany--Rome--Volcanic region of Olot in Catalonia--Cones and lava-currents--Ravines and ancient gravel-beds--Jets of air called Bufadors--Age of the Catalonian volcanos--Miocene period--Brown-coal of the Eifel and contemporaneous trachytic breccias--Age of the brown-coal--Peculiar characters of the volcanos of the upper and lower Eifel--Lake craters--Trass--Hungarian volcanos 408