THE EXTRUSIVE PROCESSES. 603 



tion of the North American, European, North Atlantic, and Arctic 

 segments, and the New Zealand volcanic region is somewhat less closely 

 related to the approach of the Australian, Antarctic, Pacific, and South- 

 ern oceanic segments. Nearly all of these angular conjunctions involve 

 two depressed segments joining two relatively elevated segments. 

 This relationship suggests a causal connection between the intensified 

 movements at these angular conjunctions and the intensified volcanic 

 action of these regions. There are enough volcanoes, however, that 

 do not fall into these groups, or apparently into any other grouping, 

 to suggest that the development of volcanoes is not wholly dependent 

 on any surface relationship, but that it is connected ^\'ith deep-seated 

 causes that are indeed modified, but not wholly controlled, by sur- 

 face conditions, or even by the movements of the master segments of 

 the earth's crust. 



4. In latitude. — The distribution of volcanoes appears to have no 

 specific relation to latitude. Mounts Erebus and Terror, amid the ice- 

 mantle of Antarctica, and Mount Hecla in Iceland, as well as the numer- 

 ous volcanoes of the Aleutian chain, give no ground for supposing that 

 volcanoes shun the frigid zones. On the other hand, the numerous 

 volcanoes of the equatorial zone do not imply that they avoid the 

 torrid belt. Their distribution appears to be independent of latitude. 

 This is not cited because of any supposed effects of external temperar 

 ture, for that must be trivial, but because it bears on the question 

 whether strains are now arising from the supposed slackening of the 

 earth's rotation, which have any connection vrith. volcanic action. If 

 the oblateness of the earth is decreasing, the equatorial belt must be 

 sinking and growing shorter, and hence must be under lateral pressure, 

 while the polar caps must be rising, and increasing their curvatures, and 

 should be under tension. These conditions, if real, might be supposed 

 to have something to do vrLih the extrusion of lava. Nothing in the 

 present or the past distribution of igneous action seems to afford much 

 support to this hypothetical inference. 



5. In curved lines. — In the Antilles, the Aleutian Islands, the Kurile 

 Islands, and in other instances, there is a notable linear arrangement of 

 volcanoes with appreciable curvature. It has been noted that the 

 convexity of the curves is turned toward the adjacent ocean. In some 

 cases, however, there is a notable linear arrangement without appre- 

 ciable curvature, as in the Hawaiian range, in the recently extinct line 



