989 



discovered that it rises from aiidesite. At the northern base on the 

 beach near tiie kampong Maftutn I saw on the 1«' of September 

 1903, some cold springs appear from nnder the yellowish brown 

 tuff and below the sealevel. 



Beyond the northwest side of the outer crater-rim rises the Kota 

 IMum, which is apparently the vent^) indicated by Verbeek as the 

 north rim of the large crater-wall. Evidently it is from this vent 

 that the lavastreams were ejected that were denuded at the western 

 side of the north coast of Tidore. Further to the northwest follows 

 the Tarobo Mabulu (540 m.) and the Bulu Gambir (320 m.) The 

 order of the vents of eruption will be 4, 3, 1, and 2, while it is 

 still an open question whether 3 is older than 1. 



Concerning the rocks we can still add that Reinwardt considered 

 the un weathered material of the peak and of the whole island to 

 be basalt'). J. W. Retgers determined '"i a fragment from an obsidian- 

 like lavastream near Soa Sin as hypersthene-andesite. Another piece 

 of unknown origin proved to be pyroxene-andesite. The lavastream 

 at the south base near campong Seli also belongs to this group of 

 rocks, according to Verbeek ■*), Nothing is known as yet concerning 

 the petrographical character of the volcanoes lying between the peak 

 and the volcano of Maftutu. But near Akè Sahu at the east base of 

 the above-mentioned tnountain Verbeek found the following profile: 

 Substratum of i^ m of andesite, upon this 1^ m of tuff, then Vi "^ 

 of yellow tuff and superposed on this 6 or 7 m of pumicestoiie-tuff '). 



The above-mentioned, horizontally stratified, yellowish brown tuff 

 near the campong of Maftutu proved to be an andesitic tuff, easy 

 to pulverize. The numerous rock-fragments enclosed in it are gene- 

 rally not bigger than grains of sand; only some fetch a diameter 

 of Vü c.m. Under the microscope the fragments present structures 

 that prove them to belong to several varieties of andesites, (nostly 

 to the pyroxene-andesites. Some, however, contain barkevitic amphi- 

 bole. The groundmass of these rocks is felsite-like or hyaline. In 

 the latter case it also encloses numerous angite-microlites. The fel- 

 spars — mostly plageoclases — are most often quite fresh and 

 clear as glass. The cement consists of a powdery and highly decom- 

 posed debris of rocks, mixed with numerous brownish-yellow par- 



1) L.c. Bijlage V, fig. 128. 



2) L.c. p. 499. 



3) Mikroskopisch onderzoek van gesteenten uit Neder!. Oost-lndië. Jaarboek van 

 het Mijnwezen in N. O. 1. 24. Wet. gedeelte. Amsterdam 1895, p. 120. 



*) L.c. p. 251. 



s) L.c. Bijlage V, fig. 129. 



