374 GEOLOGY 



2. Relative to land and sea. The active volcanoes of the present 

 time are located chiefly along the borders of the continents, and 

 within the great oceanic basins (Fig. 295). On this account, the 

 sea-water has often been supposed to have some causal connection 

 with volcanic action, and the presence of chlorine in the volcanic 

 gases has been urged in support of this view. Volcanoes, however, 

 are not distributed so equably and exclusively about the several 

 oceans as to give this conclusion force, though the basins, as basins, 

 probably favor vulcanism. Volcanoes are numerous within and 

 around the Pacific, the greatest of the oceans; but they are not 

 especially abundant in or about the Atlantic, while they are 



Fig. 294. Sketch of the crater of cinder cone near Lassen Peak, Cal., show- 

 ing the peculiar feature of two rings. The funnel is 240 feet deep. (U. 

 S. Geol. Surv.) 



numerous in and around the Mediterranean, a much smaller body 

 of water. On the other hand, there are existing or very recent 

 volcanoes in the interior of Asia, Africa, and America. If volcanoes 

 were dependent upon proximity to the sea, they should have had 

 close relations to it in the past, as much as now; but in recent 

 periods there has been much volcanic activity in the plateau 

 region and even in the plains region of western America, and in the 

 heart of Asia and Africa, far from the ocean. In older periods, it 

 is still less clear that there was any connection between volcanoes 

 and surface waters. 



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 movement in com- 

 paratively recent times, or are still moving. The great mountain 

 belt stretching from Cape Horn to Alaska and thence onwards 



