In the common well-known alypical complexes of llie B-Wn-iu we 

 never see this rcciiiTOiil wave and in the rare clinical cases with 

 recurrent anricle wave it is seen after the /?-wavc. Though this 

 seeming' discrepancy can be accounted tor, we may perhaps find a 

 fuller explanation after a continued research. 



Geology. -- ''(hi komoeogeneous inchmons of Kaioah Idjen, Goentoer 

 and Kvakatau and their connection ivith the surrounding erup- 

 tive roch." By H. A. Brouwer. (Communicated by Prof. G. 



A. F. MoLENfiRAAFF.) 



(Communicated in the meeting- of b'ehinaiy '28, 1914). 



From the study of homoeogeneous inclusions of eruptive rocks it 

 is apparent which rocks of great depth may crystallize out of the 

 mothermagma, and to wliich differentiations this magma was subject 

 during the formation of a certain volcanic complex, even when the 

 eruptive aequivalents of certain products of differentiation, occurring 

 among the inclusions, are not known among the volcanic rocks ot 

 the complex. Further, they show us the conditions of crystallization 

 of certain minerals, which only under special conditions can be 

 formed out of a magma of a certain chemical constitution ^). For 

 the determination of the relative age of rocks of the sarne volcanic 

 complex the study of inclusions is an important resource, especially 

 for the Indian volcanoes, which for the greater part are built up from 

 loose rolled material, natural denudations being of little occurrence. 



Kawah Idjen. 



The volcanic products of the Kawah Idjen '") consist chiefly of cinders 

 and stones, which are partly hardened into a conglomerate and are 

 beautifully denudated in the precipitous walls that surround the lake 

 of the crater. Somewhat above the locks of the irrigation which 

 when the level is high unloads the lake, there begins a flow of 

 lavas that follows the left shore of the drainage. Along the precipi- 

 tous slope to the locks and in the stream of lavas, during a short 

 visit in August 1912, some homoeogeneous and enallogeneous inclu- 

 sions were collected. The enclosing rocks are hypersthene-augite- 

 andesytes, in which numerous light-coloured phenocrists of plagioclase 

 form a contrast with the gray to grayish black glassy groundmass. 



1) A. Lacroix, Les enclaves ties lochcs volcaniques Macon 1894. Id. La Montagne 

 Pelée et ses eruptions, Paris. 1904. 



2) R. D. M. Verbeek and Fennema, Java en Madoera I. p. 81. Amsterdam 1896. 



