Ch. XIV.] KAVINE3 IN LAVA EXCAVATED BY RIVER?. 189 



pebbles and angular fragments of rock ; in other places fine 

 earth, which may have constituted an ancient vegetable soil. 



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 eighteen feet of underlying limestone. Occasionally 

 an alluvium, several feet thick, is interposed between the igne- 

 ous and marine formation ; and it is interesting to remark, that 

 in this, as in other beds of pebbles occupying a similar position, 

 there are no rounded fragments of lava, whereas, in the modern 

 gravel beds of rivers in this country, volcanic pebbles are 

 abundant. 



The deepest excavation made by a river through lava, which 

 I observed in this part of Spain, is that seen in the bottom of 

 a valley near San Feliu de Pallerdls, 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 probably required for the erosion 

 of so deep a ravine ; but we have no reason 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 an equal quantity of time. 



We shall describe one more section to elucidate the phe- 

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

 of hills to the east of Olot, descends a considerable slope 

 until it reaches the valley of the river Flu via. Here, for the 

 first time, it comes in contact with running water, which has 

 removed a portion,, and laid open its internal structure in a 

 precipice about 130 feet in height, at the edge of which stands 

 the town of Castell Follit. 



By the junction of the rivers Fluvia and Teronel the mass 

 of lava has been cut away on two sides ; and the insular mass 



