Geology. — "On the Rate of Denudation in Java". By Dr. L. 

 RuTTEN. (Communicated by Prof. Dr. C. E. A. Wichmann.) 



(Communicated in the meeting of November 24, 1917). 



The present investigation is based on the tables of annual content 

 of silt and of the annual estimates of the discharge of a number 

 of rivers in Java, besides on occasional estimates of the solid material 

 dissolved in their water. 



It was the interesting thesis of Dr. L. G. den Berger ^) that first 

 called my attention to the regular observations of some rivers in 

 Java and Madura in point of their discharge, the amount of dis- 

 solved materials and their silt-content. On being asked for further 

 information Mr. den Berger kindly sent me the silt- and discharge- 

 estimates for some typical rivers in Java, which valuable collection 

 was afterwards supplemented by Mr. Weber, chemist at the agro- 

 geological Laboratorium of the Department for Agriculture. I also 

 received valuable information from Dr. E. C. J. Mohr, Director of 

 this Laboratory. Some modern literature was afforded me by Dr. 

 B. G. Escher of Weltevreden. To these gentlemen I wish to express 

 m}' warm thanks for their assistance. 



With a view to difficulties of irrigation in the Serajn-system and 

 in connection with newly projected irrigation-works Mr. Mohr had, 

 in the year 1907, samples of water collected at regular intervals in 

 several places in this system, which were examined at Buitenzorg. 

 He had moreover estimates made of the discharges of these several 

 rivers. The results of this investigation '), important from an agricul- 

 tural point of view, prompted geologists to make similar observations 

 also for other projected irrigation works, which were worked out 

 later on especially by Mr. den Berger and Mr. Weber, and the 

 practical use of which appears unequivocally from the thesis 

 just alluded to. The values found were not only important for the 

 agriculturist whom they taught what he brought on the fields to be 

 irrigated, quantitatively and qualitatively, but also for the geologist, 



^) L. G. DEN Berger. Landbouwscheikundige onderzoekingen omtrent de irrigatie 

 op Java. Delft. 1915. 



') E. G. J. Mohr, Over het slibbezwaar van eenige rivieren in het Serajoedal 

 enz. Mededeelingen, uitgegeven door het Dept. van Landbouw, n''. 5. Batavia 1908. 



