990 



tides of iioiihjdroxide, which give the peculiar colour to the rock. 

 The cement contains moreover numerous splinters of felspai's and 

 augites, besides granules of black iron-ore. All this shows that this 

 tuff cannot be solidified ashes, but is to be looked upon as a con- 

 glomerated product of decomposed volcanic material. 



F'arther to the east, near the campong Sekèta I found solid ande- 

 site like that of which the campong Tjobo is made up, while in the 

 small bend near the said campong again audesite-tuff has been laid 

 bare. We can add also that on the North-West side of the island, 

 near Tandjung Rum, hornblende-, augite- and augite-andesite are found ^). 



In conclusion let it be stated that, when, iji 1858, J. H. Ckoockewit 

 picked up a piece of mica-schist behind Humboldt Bay in New 

 Guinea, Piince Amir of Tidore, who saw him do so, was induced 

 to observe: "that it was not at all of rare occurrence in Tidore" '). 

 Still, from this pronouncement we can infer only that some lustrous 

 mineral is not rare in the rocks of that island. 



1) A. WicHMANN. "Nova Guinea" 4. Leiden 1917, p. 45. 



^) "Oppervlakkige geognostische schets der bezochte punten op de zuid , west- en 

 noord-kusten van NieuwGuinea." Bijdr. t. de T. L. en Vk. (2) 5. Amsterdam 1862, 

 p. 140. 



