298 SEE— THE CAUSE OF EARTHQUAKES. [October i8, 



" Generally it would appear that these regions of instability are to be 

 found along the margins of continents or tablelands, which rise suddenly 

 to considerable heights above oceanic or other plains. 



" At the present time we may, therefore, say that megaseismic disturb- 

 ances do not occur anywhere, but only in districts with similar contours. 

 Are we dealing with primitive troughs and ridges which are simply altering 

 their dimensions under the continued influence of secular contraction, or do 

 these reliefs of seismic strain represent isostatic adjustments which denuda- 

 tion and sedimentation demand?" 



Professor Milne then discusses other possible causes, such as 

 the effects of ocean currents and the seasons, including meteoro- 

 logical causes, such as accumulations of ice and snow at the poles, 

 and finally the motion of the pole in the body of the earth ; and he 

 says that in about thirteen years between 1892 and 1904, he '' finds 

 records for at least 750 world-shaking earthquakes," which affords 

 one an impressive idea of the extent of his researches, and of the 

 importance of the subject. 



In general the geographical distribution of volcanoes is closely 

 similar to that of the earthquakes, but the latter are the more general 

 and widely extended phenomena, while the former are more special. 

 It is remarkable that the volcanoes break out in the centers of the 

 earthquake belts. This relation can not be accidental, but points to 

 a common cause underlying both phenomena. 



Besides the active volcanoes near the seashore, and on islands, 

 many of which were heaved up originally by submarine eruptions, 

 nearly every country has a long list of extinct volcanoes. The 

 islands in which volcanic eruptions have ceased, may also be viewed 

 as extinct volcanoes in the sea. In this respect the southern and 

 central Pacific Ocean is particularly rich in extinct volcanoes, and 

 there also, a great many submarine earthquakes are supposed to 

 occur. But the greatest breeding ground for world-shaking earth- 

 quakes, as Professor Milne says, are the deep troughs along the 

 continents, near which many volcanoes usually are burning. As 

 volcanic regions, we may mention, especially, the west coast of 

 South and Central America, the Aleutian and Kurile Islands, Japan, 

 the Philippines, Sumatra, Java, and adjacent islands of the East 

 Indies, New Zealand, the region of Erebus and Terror in the 

 Antarctic, and Iceland, the Caribbean Sea, with the Azores and 

 Canaries, the region of the Mediterranean and Central Asia, west of 



