62 H. I. JENSEN. 



time four violent earthquakes were experienced — appar- 

 ently brought on by a co-operation of secondary causes. 

 Of all these secondary causes the equinox is perhaps next 

 to 'perigee' the most potent, owing partly to its disturbing 

 influence on atmospheric conditions, and partly to the sun's 

 gravitational influence at such times. 



VII. The evidence afforded by the Earthquakes of Japan 

 — Milne divides the earthquakes of Japan into two classes: 

 (1) those that originate beneath tlie sea, many of which 

 are seen on the seismograph diagrams to be of the same 

 nature as explosions. (2) those that accompany folding 

 and shearing processes and the consequent fracturing of 

 strata. 1 



In regions like Japan where the rocks are largely of a 

 porous nature, percolation of water by capillarity may con- 

 stantly be admitting water to volcanic foci, and to reser- 

 voirs of hot magma such as sills or laccolites. Fissuring 

 resulting from the folding processes going on in the expand- 

 ing Tertiary rocks of Japan, and in the ocean east of Japan, 

 may also cause admission of water from the great oceanic 

 geosyncline. 



Dr. Koto, in his excellent paper on " The Scope of the 

 Vulcanological Survey of Japan," 2 divides the earthquakes 

 of his country into two classes, fa) the purely volcanic ones 

 which have a very limited area of shocks, such as that of 

 Bandaisan 1888 ; and (b) those which are tectonic in origin, 

 related to great earth movements and with shocks affect- 

 ing a wide area. Dr. Koto disagrees with Prof. J. Milne, 

 who supports the Humboldt-Naumann or vulcanistic theory 

 of earthquakes. 



1 " Earthquakes by J. Milne, pp. 228 and 281. 



8 " Publications of the Earthquake Investigation Committee," No. 3, 

 pp. 89 - 103, Tokyo 1900. 



