188 
OLDER PLIOCENE PERIOD. 
[Ch. XIV 
paratively 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 rock which bounds the 
valley. Thus, in the accompanying section, at the bridge of 
Cellent, six miles east of Olot, we see the lava on one side of 
No. 45. 
Section above the bridge of Cellent. 
a, Scoriaceons lava. 
b, Schistose basalt. 
c, Columnar basalt. 
d, Scoriae, vegetable soil, and alluvium. 
e, Nummulitic limestone. 
f, Micaceous grey sandstone. 
the small stream, while the inclined stratified rocks constitute 
the channel and opposite bank. The upper part of the lava at 
that place is scoriaceous ; farther down it becomes less porous, 
and assumes a spheroidal structure ; still lower it divides in 
horizontal plates, each about two inches in thickness, and is 
more compact. Lastly, at the bottom is a mass of prismatic 
basalt about five feet thick. The vertical columns often rest 
immediately on the subjacent secondary rocks ; but there is 
sometimes an intervention of such sand and scoria? as cover 
a country during volcanic eruptions, and which when unpro- 
tected, as here, by superincumbent lava, is washed away from 
the surface of the land. Sometimes the bed d contains a few 
