841 



is the most recent portion of the folded, sedimentary Tertiary east 

 of Biiitenzorg and is composed entirely of andesitic sandstones and 

 tufF-breccia. 



The Tjilamaja, rising on the northern slopes of the Tangkuban 

 Prahu massif, drains, according to Verbkek and Fennema's map') a 

 region of recent volcanic rocks, of old-miocene breccia, miocene 

 marls and quaternary. 1 have no personal knowledge of the system, 

 but here I feel urged to point to 'an error on a map in the archives 

 of the "Dutch Colonial Petroleum Company", on which a consider- 

 able portion of the so-called miocene breccia are indicated as 

 marls, shales and sandstones, an error quite similar to those regard- 

 ing the country east of Buitenzorg'). This requires qlialification, 

 as it appears that in the Tjilamaja system marls and volcanic rocks 

 in reality counterbalance each other, whereas according to Verbeek 

 and Fennema's map the volcanic rocks {ml and v) by far exceed 

 the marl}' rocks. 



For this river the obtained denudation value is somewhat ex- 

 aggerated* as the volume of water (5,610^ m') carried past the place 

 of observation is too near the value of the total annual rainfall in 

 the system above the place of observation (6,8 10* m'). Anyhow in 

 the system of the Tjimanuk young volcanic rocks prevail. In its 

 northern career the river also drains a small tract of miocene marls, 

 it not being excluded that in the large tract of "miocene breccia", 

 southwest of the G. Tjerimai, there still occur marls in a rather 

 considerable quantity. 



With regard to the Tjimanuk the obtained annual denudation is 

 most likely an understatement, as the volume of water (2 — 3 10' m*) 

 passing the place of observation is too small a portion of the total 

 rainfall in the system (9 — 10 10' m'). True, in this extensive system with 

 so many sawahs the water evaporates on a large scale, but the obtained 

 ratio seems to be too low an estimate of the remaining tlow of rainwater. 



In the Kali Tandjum system young volcanic rocks, miocene 

 breccia and miocene marls occur above Tipar, the place of obser- 

 vation. On Verbeek and Fennema's map, however, the volcanic rocks 

 {vd and v) far preponderate over the clayey marly i-ocks. 



The Kali Seraju system is one of the most "mingled" systems 

 of all Java, as it includes beside large tracts of marls, miocene 

 breccia and recent volcanic rocks, also eocene and cretaceous rocks. 



The Djragung and the Pengaron derive part of their water from 



1) See note 1 foregoing page. 



2) L. RuTTEN. ''Old Andesites" and "Brecciated Miocene" east of Buitenzorg. 

 Proceed, of the Royal Acad. Vol. XX. Amsterdam 1918, p. 597—608. 



