426 KEPOKT— 1886. 



One feature exhibited by the table is, that the rocks of Oshima, Fuji- 

 san, and Tonosawa are basic, while those like Chokaisan and Moriyoshi- 

 yama, belonging to the Honshiu line of volcanoes, are relatively acidic. 

 More extended observations of this description may show that different 

 lines of volcanoes have erupted different lavas, or that the lavas of different 

 constitution are of different ages. 



6. Magnetic Character of Bocks. 



Mr. E. Kinch, when speaking of the soils in the neighbourhood of 

 Tokyo, makes special reference to the magnetite they contain. A great 

 portion of this comes from the disintegration of volcanic rocks. Many of 

 the Japanese lavas have a distinct effect upon a compass needle. The 

 black lavas from the crater of Pujisan will deflect the needle of an ordi- 

 nary compass through 180 degrees. Many of the pieces of lava are not 

 only magnetic, but they are polar. Dr. E Naumann found a block of 

 augite-trachyte on the top of Moriyoshisan which would deflect the needle 

 of a compass through 155°. 



The most curious observation made by this investigator was that the 

 magnetic declination near to Ganju-san has during the last 80 j'ears 

 (when it was about 14.30 E.) decreased 19°, it now being about 5° W. 

 As we recede from this mountain the amount of change has been less. 

 Assuming this result to be correct, it would seem justifiable to look 

 towards Ganju-san as connected with these local changes. Some of the 

 volcanoes in the Kuriles are said to exert a marked influence upon the 

 compasses of ships. When a vessel is lying near certain mountains, as 

 for instance in Bear Bay, at the north end of Iturup, a distant mountain 

 has a very different bearing to that which is indicated by the same com- 

 pass when the vessel is a short distance outside Bear Bay. 



In both cases the ship may be lying in the same direction, and the 

 direction of observation is practically along the same line. 



This leads me to repeat a suggestion that 1 have several times made 

 during the last few years, namely, that a magnetic observatory be' esta- 

 blished on or near one of the more active volcanoes of this country. 

 Many of these volcanoes, like that of Oshima (Vries Island), lie in the 

 track of so many vessels that to determine whether local and rapid 

 changes in magnetic declination are taking place in these localities appears 

 to be a legitimate investigation. Changes in volcanic activity are pro- 

 bably accompanied by local changes in the magnetic effects produced by 

 subterranean volcanic magmas. These changes may be due to alterations 

 in position, alterations in chemical constitution, and changes due to the 

 acquisition or loss of heat. If such is the case, the records of a magnetic 

 observatory would lead us to a knowledge of changes taking place beneath 

 the ground. When we remember that volcanoes like Oshima (Vries 

 Island) lie in the track of so many vessels where it seems probable that 

 there may be local and rapid changes in magnetic variation taking place, 

 it seems that the suggested investigations have a practical as well as 

 scientific aspect. An investigation of earth-currents at and near volca- 

 noes might be added to the magnetic investigations. 



7. Intensity of Eruptions. 



Judging from the accounts of eruptions which have been given in the 

 preceding pages, it would appear that the intensity of volcanic action iu 



