54 H. I. JENSEN. 



Prom this we may conclude that the wetter seasons 

 accompanying a sunspot maximum lead to increased perco- 

 lation, and may in such cases help to produce volcanic 

 eruptions, especially when, as in the case of Vesuvius in 

 1872, meteorological conditions are favourable or gravita- 

 tional influences are at work. 



Many of the eruptions referred to in my previous paper 

 as not iitting in with the theory which I advanced, fall in 

 this category. The great Javan eruptions of Papandayang 

 1772, Tomboro 1815, and Krakatoa 1883, all occurred in 

 years of sunspot maxima ; but Java is one of the abnormal 

 areas, referred to above. It is a region undergoing eleva- 

 tion and folding, and its rocks are composed almost wholly 

 of porous Tertiary sedimentaries and volcanic tuffs. 



The main uplift thai made Java a low plain (according to 

 Messrs. Verbeek and Fennema), took place in the Pliocene. In 

 the Pleistocene, Borneo, Sumatra and Java, were connected with 

 one another, and with the Asiatic continent. Violent volcanic 

 action now set in and folding commenced. During Quaternary 

 and Recent times these processes have built up the mountains of 

 Java, though they also were the cause of local subsidences and the 

 reseparation of the main islands of the Malay Archipelago. (See 

 " Description Geologique de Java et Madoura " : Troisieme Section 

 i.e. ' Geologie generale de Java,' pp. 995 - 1034 ; and ' Les Sedi- 

 ments Quaternaire,' p. 1019, by Verbeek and Fennema. See also 

 their geological map of Java and Madoura accompanying their 

 work). 



The geological history of Java beautifully illustrates the process 

 of mountain building. First we have the rise of isogeotherms 

 causing a general uplift ; then the commencement of folding and 

 volcanic action (here in Pleistocene times); lastly volcanic extra- 

 vasation and the formation of subsidence areas (Senkungsfelder). 

 We see also that volcanic action is a concomitant of mountain 

 building. Rise of isogeotherms and folding are still in progress 

 in Java, hence volcanic action is still violent. [H.I.J,] 



