421 



anee, and may even be waTiting in siiiceons deposits, i.e. the cherts 

 and hornstones, which are predominantly composed of tests of 

 radiolavia. 



I have observed manganese accunudated as grains in the folhiwing 

 deep-sea rocks : 



a. in red iimeless siliceous chiysliales with radioloria, probably 

 of Jurassic age, which are the prevailing rocks in the entire area of 

 the Danan-forraation of Central-Borneo, and in lesser quantities also 

 in the cherts, jaspers and hornstones, which occur interstratified 

 between the layers of the clayshales. 



b. in red and brown, mostly Iimeless, siliceous clayshales of triassic 

 age in several localities spread over the island of Timor, and also 

 less abundant in the nodules and layers of cliert and hornslone 

 accompanying these shales. 



c. in siliceous limestones, marls') and more or less siliceous and 

 calcareous clayshales with radiolaria, as well as in the nodules and 

 layers of hornstone contained in those rocks of Jurassic age which 

 occur very plentiful in a great portion of the island of Timor. 



d. in Jurassic deep-sea deposits on the island of Rotli'), being 

 identical which those just mentioned from Timor. 



Probably the precipitation and accumulation of manganese is 

 always initiated by the formation of such grains and a gradual 

 transition can be observed between this mode of concentration and 

 others by which the ore is more strongly localized. 



2. an nodules. Nodules of manganese are accumulations or rather 

 concretions of larger size than grains, being either perfectly round, 

 or more irregular and nodular, but always well rounded'). They 



1) The strong proportion of lime contained in these rocks gives rise to the 

 question, whether the Jurassic deep-sea deposits of Timor and Rottl, although 

 they are formed far from land and thus truly oceanic, might have been deposited 

 in water less deep than the sea, in which the entirely Iimeless precretaceous 

 deep-sea deposits of the Danauformation of Central-Borneo have been formed 

 The author intends to discuss elsewhere the far reaching problem, connected with 

 this question. 



3) Possibly also triassic and cretaceous deposits are comprised within this series 

 of folded strata. Compare H. A. Brouwer. Voorloopig overzicht der geologie van 

 het eiland Rotti. Tijdschr Kon. Ned. Aardr. Genootsch 2, XXXI, p. 614, 1914. 



3) As far as the shape is concerned, the nodules found in radiolarites of Jurassic 

 age on llie island of Rotti, are in every respect similar to those which have been 

 dredged at great depths from the bottom of the ocean Compare J. Murray and 

 .1. Hjort. The depths of the ocean p. 156: "The commonest form of the 

 manganese nodules is that of more or less rounded nodules . . . looking like 

 marbles at one place, like potatoes or like cricket balls at other places'". 



