Ch. XXXI.] 



PLIOCENE VOLCANOES. 



671 



In several localities, beds of sand and ashes are interposed between 

 the lava and subjacent stratified rock, as may be seen if we follow 

 the course of the lava-current which descends from Las Planas 

 towards Amer, and stops two miles short of that town. The river 

 there has often cut through the lava, and through 18 feet of under- 

 lying limestone. Occasionally an alluvium, several feet thick, is 

 interposed between the igneous and marine formations ; and it is 

 interesting to remark that in this, as in other beds of pebbles occu- 

 pying a similar position, there are no rounded fragments of lava ; 

 whereas in the most modern gravel-beds of the rivers of this country 

 volcanic pebbles are abundant. 



The deepest excavation made by a river through lava, which I 

 observed in this part of Spain, is seen in the bottom of a valley near 

 San Feliu de Pallerols, opposite the Castell de Stolles. The lava 

 there has filled up the bottom of a valley, and a narrow ravine has 

 been cut through it to the depth of 100 feet. In the lower part the 

 lava has a columnar structure. A great number of ages were proba- 

 bly required for the erosion of so deep a ravine ; but we have no rea- 

 son to infer that this current is of higher antiquity than those of the 

 plain near Olot. The fall of the ground, and consequent velocity of 

 the stream, being in this case greater, a more considerable volume of 

 rock may have been removed in the same time. 



I shall describe one more section (fig. 722) to elucidate the phe- 

 nomena of this district. A lava-stream, flowing from a ridge of hills 



Fig. 722. 



Section at Castell Follit. 



A. Church and town of Castell Follit, overlooking precipices of basalt. 



B. Small island, on each side of which branches of the river Teronel flow to meet the 



Fluvia. 



c. Precipice of basaltic lava, chiefly columnar, about 130 feet in height. 



d. Ancient alluvium, underlying the lava-current. 



e. Inclined strata of sandstone. 



on the east of Olot, descends a considerable slope, until it reaches 

 the valley of the river Fluvia. Here, for the first time, it comes in 

 contact with running water, which has removed a portion, and laid 



