194 



PHYSIOGRAPHY. 



[chap. 



is an ideal section of a volcano, showing the dykes of lava 

 running through the stratified deposits, and also showing 

 two minor cones a b, thrown up at points where the volcanic 

 matter has been able to force its way to the surface. Mount 



Fig. 52. — Breached Volcanic Cones, Auvergne. 



Etna is remarkable for having its flanks studded with para- ' 

 sitic cones, some of which are of considerable size, one 

 being upwards of 900 feet in height. 



After a volcano has long been silent and the large crater 



Fig. 53. — Diagrammalic Section of Volcano, with Dykes and Minor Cones. 



has been more or less filled, partly by ejected materials 

 which had fallen back into the cavity during the last 

 eruption, and partly by matter washed in by rain, renewal 

 of activity through the old channel may give rise to the 



