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, Scoriaceous lava. 



b, Schistose basalt. 

 Cy Columnar basalt. 



//, 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 scoriae 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 



