250 Messrs. R. B. Newton and R. Holland on some 



fairly abundant, being rather more easily discernible near the 

 outer surface, where they occur as reddish-brown casts, con- 

 siderably decomposed. Two microscopical sections have been 

 made from boulder no. 984, which is a matrix of black colour 

 and crowded with Nummulites. None of the other boulders 

 having been fractured, we are unable to say anything 

 respecting their internal characters. 



All the boulders were obtained from the river-beds of 

 Embalau, Tekelan, and Sajang, offshoots of the great Kapuas 

 River in its uppermost regions, being numbered as follows 

 under a group termed Series I. : — 



No. 082. Eiver Tekelan. 



983. River Embalau (right bank), \ kilom. below R. Sajang. 



984. River Embalau. 



9S4. 

 985. 

 986. 

 987. 



River Tekelan. 



The distinguishing numbers on the microscopical sections 

 are : — 



V. 1648 & V. 1650, made from Boulder no. 984. 



V. 1644, V. 1645, V. 1646, and V. 1647, made from Boulder no. 986. 



(4) Age of the Specimens. — In determining the geological 

 horizons of the specimens described in this paper we have 

 been mainly guided by the carefully worked out results of the 

 Javan Foraminifera as set forth in Verbeek and Fennema's 

 important monograph entitled ' Description ge'ologique de 

 Java et Madoura.' The authors mentioned have limited 

 Orbitoides to two subgenera instead of five as originally 

 proposed by Giimbel, viz. Discocyclina and Lepidocyclina, 

 characteristic of different parts of the Tertiary system. As we 

 show later on, Messrs. Verbeek and Fennema hold that 

 Discocyclina ', having simple rectangular chambers in the 

 median plane, as found in the Indian Archipelago, belongs 

 entirely to Eocene and Oligocene rocks ; whereas Lepido- 

 cyclina, with rounded chambers, never occurs in this area in 

 older deposits than Miocene, and apparently becomes extinct 

 during Pliocene times. Similarly with regard to the Nummu- 

 lites we can recognize an Eocene and Oligocene age respec- 

 tively for Nummulites javanas and N. Djokdjokartos, species 

 found both in Borneo and Java. 



The foregoing considerations would lead us to conclude 

 that the Malinam-River pebbles may be referred to two 

 periods — (1) an Eocene, determined by the presence of 



