Ch. XXXI.] 



MIOCENE VOLCANIC ROCKS. 



537 



of a single liouse, was cast down by an earthquake ; one of those shocks 

 which, at distant intervals during the last five centuries, have shaken the 

 Pyrenees, and particularly the country between Perpignan and Olot, 

 where the movements, at the period alluded to, were most violent. 



The annihilation of the town may, perhaps, have been due to the cav- 

 ernous nature of the subjacent rocks ; for Catalonia is beyond the line of 

 those European earthquakes which have, within the period of history, de- 

 stroyed towns throughout extensive areas. 



As we have no historical records, then, to guide us in regard to the 

 extinct volcanos, we must appeal to geological monuments. The annexed 

 diagram, fig. 671, will present to the reader, in a synoptical form, the re- 

 sults obtained from numerous sections. 



The more modern alluvium (d) is partial, and has been formed by 



Supei'position of rocks in the volcanic district of Catalonia. 



a. Sandstone and nummulitic limestone. 

 h. Older alluvium without volcanic pebbles. 

 c. Cones of scorite and lava. 



d. Newer alluvium. 



the action of rivers and floods upon the lava ; whereas the older gravel 

 (h) was strewed over the country before the volcanic eruptions. In 

 neither have any organic remains been discovered ; so that we can merely 

 affirm, as yet, that the volcai:os broke out after the elevation of some 

 of the newest rocks of the nummulitic (Eocene) series of Catalonia, and 

 before the formation of an alluvium (d) of unknown date. The integrity 

 of the cones merely shows that the country has not been agitated by vio- 

 lent earthquakes, or subjected to the action of any great flood since their 

 origin. 



East of Olot, on the Catalonian coast, marine tertiary strata occur, 

 which, near Barcelona, attain the height of about 500 feet. From the 

 shells which I collected, these strata appear to correspond in age with the 

 Subapennine beds ; and it is not improbable that their upheaval from 

 beneath the sea took place during the period of volcanic eruption round 

 Olot. In that case these eruptions may have occurred at the close of the 

 Older Pliocene era, but perhaps subsequently, for their age is at present 

 quite uncertain. 



Volcanic rocks of the Eifel. — The chronological relations of the vol- 

 canic rocks of the lower Rhine and the Eifel are also involved in a con- 

 siderable degree of ambiguity ; but we know that some portion of them 

 were coeval with certain tertiary deposits called " Brown-Coal" by the 



