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



influence of bending. The after-shocks which so frequently follow large 

 earthquakes announce that the disturbed strata are gradually accommodating 

 themselves to their new position." 



Professor Milne's statement that " the greater number of this 

 series (10,000 Japanese earthquakes) originated beneath the ocean 

 or along the seaboard, and as they radiated inward they became more 

 and more feeble, until, on reaching the backbone of the country, 

 which is drilled by numerous volcanic vents, they were almost 

 imperceptible " seems to point directly to the cause set forth in this 

 paper. If earthquakes depend upon the explosive power of steam, 

 they ought not to be numerous near the volcanoes (unless these 

 vents get stopped up), but they ought to be very numerous under 

 the sea in the deep trough just east of Japan, which he says is found 

 to be true by laborious and extensive observations covering a vast 

 number of these phenomena. In order to leave no doubt as to the 

 significance of these results we shall consider also the other lines of 

 thought which he has worked out with so much care. 



§ 4. Inadequacy of the tectonic theory based on slipping and 

 bending, and dislocational and fault movements. 



At present we shall not touch upon all the questions discussed 

 by Professor Milne, but we may remark that slopes of i in 20 given 

 above probably are not great enough to produce the least slipping, 

 or fracturing or bending of rocks. The most effectual way to 

 convince ourselves of the truth of this view is by an appeal to the 

 cones of actual volcanoes. Take Mount Cotopaxi, for example. It 

 is one of the tallest active volcanoes in the world, and the most 

 regularly built of all the large volcanoes. The slope is 30°, the 

 angle of the apex being 120°. A slope of 30° corresponds to i in 

 1.732; and thus Professor Milne's ratio of i in 20 is less than one- 

 tenth that required to produce stability; and it has escaped his 

 notice that slopes steeper than i in 35 are not such that the steepness 

 could give rise to submarine earthquakes and their accompanying 

 landslips. If the cones of volcanoes like Cotopaxi do not slip, when 

 they are more than ten times steeper than the steepest sea slopes, 

 and over twenty times that mentioned as unstable by Professor 

 Milne, why should slips occur under the sea? Obviously the steep- 

 ness, though no doubt considerable in certain places, is not the cause 



