670 



VOLCANOES OF CATALONIA. 



[Ch. XXXL 



Kg' 720. the most part removed. The cur- 



rents of lava in Catalonia, like 

 those of Auvergne, the Yivarais, 

 Iceland, and all mountainous coun- 

 tries, are of considerable depth in 

 narrow defiles, hut spread out into 

 comparatively thin sheets in places 

 where the valleys widen. If a 

 river has flowed on nearly level 

 ground, as in the great plain near Olot, the water has only excavated 

 a channel of slight depth ; but where the declivity is great, the 

 stream has cut a deep section, sometimes by penetrating directly 

 through the central part of a lava-current, but. more frequently by 

 passing between the lava and the secondary or tertiary rock which 

 bounds the valley. Thus, in the accompanying section (fig. 721), at 



a. Conglomerate. 



5. Thin seams of volcanic sand and scoriae. 



Fig. 721. 



Section above the bridge of Cellent. 



d. Scoriae, vegetable soil, and alluvium. 



a. Scoriaceous lava. 

 &. Schistose basalt. 

 c. Columnar basalt. 



e. Nummulitic limestone. 

 /. Micaceous gray sandstone. 



the bridge of Cellent, six miles east of Olot, we see the lava on one 

 side of the small stream ; while the inclined stratified rocks consti- 

 tute the channel and opposite bank. The upper part of the lava at 

 that place, as is usual in the currents of Etna and Vesuvius, is scoria- 

 ceous ; farther down it becomes less porous, and assumes a spheroidal 

 structure ; still lower it divides in horizontal plates, each about 2 

 inches in thickne-ss, and is more compact. Lastly, at the bottom is a 

 mass of prismatic basalt about 5 feet thick. The vertical columns 

 often rest immediately on the subjacent stratified rocks ; but there is 

 sometimes an intervention of sand and scoriae such as cover the coun- 

 try during volcanic eruptions, and which, unless protected, as here, by 

 superincumbent lava, is washed away from the surface of the land. 

 Sometimes the bed d contains a few pebbles and angular fragments 

 of rock ; in other places fine earth, which may have constituted an 

 ancient vegetable soil. 



