( 227 ) 



are still extant, that of Rin(leii,ü;au notwitiislainiiiif;- its f>"realei- Iieigiit 

 has reiiiaiiied in belter coiidiliün, and that there the contrast between 

 edge and bottom is more marked than that at tiie Sempoe-crater, 

 we may cojichuk' that the former crater is 3 ounger, or at least has 

 come to rest later than the other one. In that part of the system 

 where the two craters as it were interfere the Rindengan-wall, the 

 spot indicated on the map as K^r^tengcn, is continned almost without 

 interruption, aiul the uncertain relief is turned towards the Sempoe- 

 side. The circular ])lain is here at the side of the solfatai'e still 

 interruj)ted by a low irregular ele\ation. Of course the fad that on 

 the whole the bottom of the Sempoe-crater lies more than l(K) ^1. 

 higher than the Rindengan-bottoni may have some intlueuce in this 

 respect; but 1 think that the relief in the central |)art would show 

 a quite ditferent as[)ect if the former had come to rest at the same 

 time as or later than Rindengan. 



The Sempoe-crater has an almost circidar shape with a diameter 

 of 2,8 to 3 KM. The dimensions of the Rindengan-crater cannot be 

 given because the south- and west-side are made uncertain by 

 Sopoetan, and the map is incomplete towards those sides. It seems 

 that this crater had an elongated sha])e extending from NNE — SSW. 

 From the map we tiud a minimum length of 2,8 and breadth of 

 ±1,(SKM. These are for the Indian Archipelago not excessive dimen- 

 sions ; but they are of sufficient importance to conclude, that the 

 ejected mass, if nearly adecjuate to the size of these vents, must to 

 a great distance prevail in the [)etrographical comj)osition of the 

 surrounding territory. 



Now the central part of the Minahassa consists, as far as \isible, 

 chietly, and southward of the Sopoetan-mountains under the thin 

 covernig of Soi)Oetan-sands even entirely of pumice-tufa, partly in 

 strata. The igneous i-ucks of the Minahassa-volcanoes belong chieliy 

 to andesite ^) and their dark colour, also in the slaggy or punuceous 

 varieties, often also the presence of chrysolite point to basic com- 

 position. This * is especially true for the material |)roduced by the 

 volcanoes in the historical period ; (Sopoetan s.s., Hatoe Angoes and 

 Batoe Angoes baroe). The material of Sopoetan proj^er is distinguished 

 from all the other igneous rocks by the constant presence of much 

 chrysolite, thereby showing great affinity to basalt. The rule that if 

 in different periods of the eru[)ti\ily, the magma is varyim; in 

 composition, the youngest magma is the more basic, may not always 



') Compare I'rof. Dr. H. IJückinu : büilrügu zur Licoloi^iu von Celebes ; S.iiniiilungeii 

 des Ceol. Keichö-Museums in Leiden. Ser. I, Vol VU, part f, page I'J'.J — "J0:2. 



