54 VULCANISM ITS NATURE AND FUNCTION. 



misconception. All the older lands have been repeatedly 

 under the sea, and have suffered at each depression and re- 

 elevation the denuding effects of wave and tidal action. 

 Even since their latest re-elevation, the rains, frosts, and 

 rivers have been incessantly wearing, wasting, and eroding 

 so much so, that the older mountain-ranges are but the 

 merest skeletons of what they once were. Vulcanic agency 

 may block out, as it were, the contours and profiles of the 

 land ; but the meteoric and aqueous agents the frosts, 

 rains, rivers, and waves are the busy chisellers that are 

 for ever conferring upon it its latest features the latest, 

 but never the last. 



In looking upon the more ancient hills, as well as upon 

 existing volcanoes, a question naturally arises Are these 

 elevations chiefly uplif tings of the earth's solid crust, or are 

 they accumulations of igneous matter that have been dis- 

 charged from its interior ? In other words, are mountains 

 and mountain-ranges mainly produced by upheavals or 

 swellings-up of the earth's rocky crust, or have they been 

 accumulated on the surface by repeated discharges of vol- 

 canic matter 1 Much controversy has existed on this point, 

 and many arguments adduced on both sides ; but the truth 

 seems to be, that the forces from within have acted in both 

 ways partly by elevation of the stratified crust, but chiefly 

 by the accumulation of erupted materials. In this view 

 every mountain and mountain-range becomes a matter of 

 slow and gradual growth, every shower of ashes and stream 

 of lava adding to the bulk of the isolated cone, and every 

 new cone adding another link to the mountain-chain. We 

 have no exact measure of this slow and gradual accumula- 

 tion, but judging from the small amount that has been 

 added to Etna and Vesuvius during the historical period, 

 many of the existing volcanoes must be of vast antiquity ; 

 and when we carry our retrospect back through the extinct 



