ON THE VOLCANIC PHENOMENA OF JAPAN. 42S 



100 such mountains in the Japanese empire. These mountains are 

 distributed as follows : 



-- ^, T> • ( Kmiles 23 



Northern Eegion jyezo 28 



(■Northern Honshiu "j 

 Central Region \ Central Honshiu I 35 



( Oshima Group j 



' Southern Honshiu .1 



Southern Eegion -I Kiushiu > j^g 



( Southern Islands I 



Total .... 100 



If we add to our list the ruins and basal wrecks of volcanic cones, this 

 number is considerably increased. 



The number of mountains which are easily recognisable as being of 

 volcanic origin as given in the map is 129. 



Of this number about 51 are still active, that is to say, are now giving 

 off steam. These active volcanoes are distributed as follows : 



Northern Eegion {y^o^^, ' 'n} ^"^ 



Central and Southern Eegion . 24 



Total 51 



Out of the 129 volcanoes, 39 are symmetrically formed cones. 



The greatest proportion of regularly formed mountains and of 

 mountains yet giving off steam are in the Kuriles. From this it may be 

 argued that the mountains in the north are younger than those in the 

 middle and south. 



3. Number of Eruptions. 



Altogether in the preceding pages about 233 eruptions have been 

 recorded. The distribution of these in the different districts, and with 

 regard to time, is shown in the accompanying table. The greater num- 

 ber of records in the southern districts, as compared with the northern 

 districts, may be accounted for by the fact that Japanese civilisation 

 advanced from the south. In consequence of this, records were made of 

 various phenomena in the south, while the northern districts were un- 

 known and unexplored regions. The greater number of eruptions have 

 taken place in the months of February and April. Comparing the fre- 

 quency of eruptions in the different seasons, the volcanoes of Japan 

 appear to have followed the same law as the earthquakes ; a greater num- 

 ber of eruptions having taken place during the cold months. This 

 ■winter frequency may possibly be accounted for in the same manner that 

 Dr. Knott accounted for the winter frequency of earthquakes. During 

 the winter months the average barometric gradient across Japan is 

 steeper than in summer. This, coupled with the piling up of snow in 

 the northern regions, gives rise to long -continued stresses, in consequence 

 of which certain lines of weakness of the earth's crust are more prepared 

 to give way during the winter months than they are in summer. 



