. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 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 mari
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 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. 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 heigh
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