THE EXTRUSIVE PROCESSES, 



601 



3. Relative to crustal deformations. — The distribution of present 

 and recent volcanoes is much more suggestively associated with those 

 portions of the crust that have undergone notable changes in position 

 in comparatively recent times. The great '^ world-ridge" stretching 

 from Cape Horn to Alaska and thence onwards along the east coast 

 of Asia is a striking instance, for it is dotted throughout with 



Fig. 461. — ^Active volcanic area at the junction of the continental segments of North 

 and South' America, and of the abysmal segments of the Atlantic and Pacific. 

 Jones Relief Globe. (Photo, by R. T. Chamberlin.) 



active and recently extinct volcanoes. The tortuous zone of moun- 

 tainous wrinkles that borders the Mediterranean and stretches thence 

 eastward to the Polynesian Islands is another notable volcanic tract. 

 These two belts include the greater number of existing and recent vol- 

 canoes on the land, while the great basins associated with them embrace 

 the chief oceanic volcanoes. 



There is perhaps some significance in the fact that the most active" 

 regions of vulcanism to-day lie at the angular junctions of the great earth- 



