804 



which is found near Balik Papan in East Borneo together with 

 Alveolinella bontangensis Rutten and Lepidocydina Jiexuosa Rutten ^), 

 and with these two latter species Alveolinella globulosa Rutten and 

 Lepidocyclina spec, from the deposits here dealt with aie closely 

 related. So what we know about the foraminifera agrees with the 

 conclusion derived above from the mollusca. 



The exauHiiation of the foraminifera has also confirmed that a 

 foraminiferal (globigerina) ooze occurring on the brook T e g a 1 s a r i, 

 in the vicinity ot Nanggoelan, is equivalent with the lower Miocene 

 sediments of the West-Progo Mountains. This equivalence had formerly 

 been derived from general geological considerations. 



When attempting more accurately ro fix the age of the West-Progo 

 deposits (within the older Miocene period) in respect to the just- 

 mentioned Rembang beds, we meet with great difficulties. For the 

 foraminifera of Rembang, which have been studied by Douville '), 

 in all probability belong to the Middle Aquitanian stage, while 

 those of the West-Progo Mountains according to our present know- 

 ledge point to a younger formation, Upper Aquitanian or even 

 B u r d i g a 1 i a n. (_)n the other hand the Rembang beds, as stated 

 above, present a higher percentage of still living mollusca and on 

 this account must be considered as younger than the West-Progo beds. 



The chief difficulty is that in these latter deposits also M i o g y p- 

 sina occurs. In ray opinion it is possible, however, that this genus 

 is found in still older sediments than has been assumed until now. 

 For when grouping rocks on account of the foraminifera, hardly 

 any attention has yet been paid to the different facies, and especially 

 to the depth at which they originated. The circumstance that accord- 

 ing to the more recent investigations of Douville ') Orthophragmina 

 and Lepidocyclina occur simultaneously in the American Oiigocene, 

 which until recently was considered impossible, shows that one has 

 to be very careful when classifying deposits only on account of the 

 foraminifera. 



Meanwhile the mentioned incongruity cannot be solved for the 

 present and one must be content to assign to the deposits of the 

 West-Progo Mountains here dealt with, the general term lower 

 Miocene, without being able to clear up their relation to the Rembang 

 strata, which also belong to the lower Miocene. 



^) L. Rutten, Studiën über Foraminiferen aus Ost-Asien. (Samralgn. I. Bd. 9, 



p. 287). 



2) Les foram. d. couches de Rembang (Sammlgn. !, Bd. 10, p. 19). , 



*) Les Orbitoides de Tile de la Trinité (Compt. rend. d. séanc de I'Acad. d. 



Sciences. T. 161, p. 87. 1915). 



