296 SEE— THE CAUSE OF EARTHQUAKES. [October 19, 



4. The close geographical relationship existing between vol- 

 canoes and earthquakes throughout the world, and the part played 

 by earthquakes in mountain formation, and the eruption of volcanoes. 



These four fundamental facts seem to admit of easy and natural 

 explanation on the hypothesis that the penetration of sea water 

 develops steam just under the crust of the earth, and the result is 

 the upheaval of mountains and the eruption of volcanoes. 



§ II. Professor Milne's researches on the distribution of earth- 

 quakes. 



One of the most remarkable results of recent research is the 

 discovery of numerous regions greatly affected by submarine earth- 

 quakes, so that it is now known that these phenomena occur not 

 onl-y on land, but more especially under the sea. As we shall treat 

 of this remarkable result hereafter, we shall at present confine our 

 attention to the relations of earthquakes and volcanoes as observed 

 upon the continents. It has long been recognized that both groups 

 of phenomena occur in a series of belts, which follow the same gen- 

 eral regions of the world, along certain so-called lines of weakness 

 in the earth's crust.^ 



In a recent review of earthquakes published in the British As- 

 sociation Report for 1902, Professor John Milne has outlined twelve 

 principal seismic regions, some of them of great extent. These 

 several belts include the wide boundaries of the Pacific Ocean, the 

 Antilles and Caribbean Sea region, and the great belt beginning at 

 the Azores, and extending through the Mediterranean to the Hima- 

 layas and India. This last great belt is the only one in which the 

 sea does not predominate over the land, and even here, the sea is 

 paramount over a large part of the area included, while the rest 

 includes or lies adjacent to the highest mountain range in the world. 

 As Major Dutton has remarked, it may be doubted whether all of this 

 last region should be included in one area, except, perhaps, as an 

 outline to aid the memory ; but at all events, the Azores and southern 



^ Cf. Professor Milne's work on " Earthquakes," edition 1903. which 

 includes an excellent map of the world giving the distribution of both earth- 

 quakes and volcanoes. As earthquakes in the interior of the oceans until 

 recently were seldom recorded, unless of great violence, the earthquakes 

 charted on the map are chiefly those observed on the land, so that the centres 

 of the oceans appear unduly vacant. 



