CHAPTER XIV. 



Volcanic rocks of the older Pliocene period Italy Volcanic region of Olot in 

 Catalonia Its extent and geological structure Map Number of cones 

 Scoriae Lava currents Ravines in the latter cut by water Ancient alluvium 

 underlying lava Jets of air called ' Butadors ' Age of the Catalonian vol- 

 canos uncertain Earthquake which destroyed Olot in 1421 Sardinian vol- 

 canos District of the Eifel and Lower Rhine Map Geological structure 

 of the country Peculiar characteristics of the Eifel volcanos Lake craters 

 Trass Crater of the Roderberg Age of the Eifel volcanic rocks uncertain 

 Brown coal formation. 



VOLCANIC ROCKS OF THE OLDER PLIOCENE PERIOD. 



Italy . IT is part of our proposed plan to consider the igneous 

 as well as the aqueous formations of each period, but we are 

 far from being able as yet to assign to each of the numerous 

 groups of volcanic origin scattered over Europe a precise place 

 in the chronological series. We have already stated that the vol- 

 canic rocks of Tuscany belong, in great part at least, to the older 

 Pliocene period, those for example of Radicofani, Viterbo, 

 and Aquapendente, which have been chiefly erupted beneath 

 the sea. The same observation would probably hold true in 

 regard to the igneous rocks of the Campagna di Roma. 



But several other districts, of which the dates are still 

 uncertain, may be mentioned in this chapter as being possibly 

 referrible to the period now under consideration. It will at least 

 be useful to explain to the student the points which require 

 elucidation before the exact age of the groups about to be 

 described can be accurately determined. 



Volcanos of Olot, in Catalonia. I shall first direct the 

 reader's attention to a district of extinct volcanos in the north 

 of Spain, which is little known, and which I visited in the 

 summer of 1830. 



The whole extent of country occupied by volcanic products 

 in Catalonia is not more than fifteen geographical miles from 



