102 B. KOTO : THE GEOLOGIC STRUCTURE OF 



Though the Cretaceous occurs over a limited space in the 

 Seberuaiig, a tributary to the Kapuas river in West Borneo, 

 it only became well known through preliminary notes by Gei- 

 nitz/*^^ Among the entombed remains identified, we find Vola cf. 

 quadricostata, and Trigonia cf. limbata, indicative of the presence 

 of the Upper Cretaceous. The typical Cenomanian fossil, Or- 

 hitolina concava, Lam ark, is also found as in the Javanese Cre- 

 taceous,"*^' and the Gervillia hornee?iis,^-^ Mart, is said to occur 

 in the Sambas district. Not less interesting is the occurrence"^^ of 

 Sphcerulites and Radiolites in the south-eastern part (Martapura) 

 of the island. 



In contrast to the Cretaceous, the Tertiary terrene makes 

 up the greatest part of the area, and the outline of the island 

 is indeed determined by the extent of this formation. The high- 

 laud formation, already referred to, occurs in narrow ridges and 

 sporadic masses, serving as the back-bone and water-shed of 

 great politico-hydrographie basins. These geologic islands pro- 

 ject out between the rolling hills of the Tertiary strata, which 

 elevate themselves as they approach the central, axial highland 

 chain, lending special topograghic relief to the aspect of the 

 country. From its position the Tertiary is called collectively 

 the upland formation. Shales, micaceous sandstone and lime- 

 stone prevail throughout the area, and fall into the Older and 

 Younger Series, of which the former may be divided again into 



continent ; but these various discoveries unfortunately weaken the strength of his theory, and 

 make me almost believe the " Central Mediterranean " of the Jurassic time to extend directly 

 from tlie Atlantic to the Pacific Ocean. 



40) Zeitschr. d. d. geol. Gesell. 1883, S. 204. 



41) Martin, S'ammluiKjen, fjeol. E.-Mus., 1890, Bd. IV, S. 209-231. 



42) Ibid., Bd. IV, S. 198. 



43) Ibid., Bd. IV, S. 117. 



