Geology. — ''Old Andesites" and '^Brecciated Miocene" to the east 

 of Buitenzon/ {Java). Bv Dr. L. Rutten. (Communicated by 

 Prof. Dr. C. E. A. Wichmann). 



(Communicated in the meeting of September 29, 1917). 



In their "Geology of Java and Madoera" ^) Verbeek and Fennema 

 deal with the development of the Neogene formations about as follows : 



During the oldest period of the Miocene numerous and very 

 extensive eruptions took place all over Java ; the eruptive rocks 

 were for the greater part andesites. Where they emerge they are 

 in many cases difficult to distinguish from the andesites of the 

 present volcanoes; in other cases, however they ditfer from the 

 recent andesites in being weathered to a greater depth. 



In a subsequent period the old volcanoes were denuded again 

 considerably, their detritus forming round the volcanic nuclei a 

 system of stratified breccia, conglomerates and andesitic sandstones 

 (m 1), which may locally be found to be interstratified with clay and 

 sometimes with limestone or marl. 



This period was succeeded by one in which fine-grained layers, 

 especially marls, were deposited upon the old miocene breccia and 

 conglomerates (m 2). 



Subsequently in Ihe most recent part of the Miopliocene especially 

 limestones were formed (m 3). 



Now after the Tertiary had been folded, the present volcanoes 

 arose in Java and spread their discharge over vast areas of the 

 tertiary strata, which had meanwhile been considerably denuded. 



In the period m 1 and m 2 only few volcanic eruptions occurred ; 

 in the period ra 3 there was no volcanic activity at all. 



It is obvious, that the authors, who were thrown upon their 

 own resources when called upon to construct, in comparatively few 

 years, a geological map of an island, four times larger than Holland 

 and difficult to traverse over long distances, had to make a number 

 of working hypotheses on the stratigraphy, the tectonic and the 

 geological history of the island, if they would make anything of 

 their injunction. It will be well, therefore, to look upon their maps 

 and profiles of Java — in which their views of the neogene, as 



1) R. D. M. Vekbeek and R. Fennema, Geology of Java and Madoera. 1896. 



