490 



of the mouth of the Nanga Koli A. F. H. Heusch collected in 1890 

 according to Pannekoek ') qnartzite and greywakke(?). On the south- 

 coast at Nanga Mbawa I found granite (read quartz-diorite) and 

 gabbro') and finally in the valley of the river Ndona quartz-diorite. 

 None of these rocks were ever found as rock, they are con- 

 sequently at least "auf tertiarer Lagerstatte". They are the last 

 remains of rockmasses that got into the conglomerates by washing 

 from which they got afterwards free again. 



The oldest formations of Flores belong to the effusive rocks of 

 the character of dacites, labrador-andesites and hornblende-andesites 

 with their tufas, on which those of the limestones of the Reo-form- 

 ation and those of the tuffas of the Soa formation follow. They 

 were uncovered by subsequent elevation. Afterwards the island was 

 over its entire length the scene of violent volcanic eruptions, from 

 which the only partly known crater mountains proceeded. The 

 material produced by them consists — as far as our knowledge 

 reaches — exclusively of pyroxene-andesites belonging to the Pacific 

 type of rocks. The younger coral limestones occuriing only spora- 

 dically have only been formed after the formation of the volcanoes. 



Von Schelle's postulation that the bottom "to the north of Mount 

 Rokka is very rich in tin-ore" appears to have been not only vain 

 but also very expensive. 



Mathematics. — ''The theory of the combination of observations 

 and the determination of the precision, illustrated by means of 

 vectors." By Dr. M. J. van Uvex. (Communicated by Prof. W. 

 Kapteyn)," 



Communicated in the meeting of June 27, 1914). 



By L. VON ScHRLTKA^) and C. Rodriguez^) a method has been given 

 of illustrating geometrically the theory of the combination of oljser- 

 vations by the method of least squares, namely by means of vector 

 operations. Rodriguez however chooses in the case of rigorous equations 

 of condition another way, whilst von Schrutka, who consistently 



1) Overzicht der geographische en geologische gegevens 1. c. p. 229. 



2) 1. c. p. 229. 



3) L. VON Schrutka, Eine vektoranalytiscbe Interpretation der Formeln der 

 Ausgleichungsrechnung nach der Methode der kleinsten Quadrate. Archiv der 

 Mathematik und Physik. 3, Reihe, Bd. 21, (1913), p. 293. 



^) C. Rodriguez, La compensacion de los Errores desde al punto de visto geo 

 metrico. Mexico, Soc, Cient. "Antonio Alzate", vol. 33 (1913—1914), p. 57. 



