AEQUINOCTIA, AN OLD PALEOZOIC CONTINENT 563 



ninth and tenth groups, some of them making part of the upper 

 zone, but chiefly belonging to the middle zone. These latter 

 varieties appear principally along the eastern bank of Lake Posso 

 and north of the lake. 



With these schists of sedimentary origin, there are others 

 which must have evolved from more or less basic eruptive rocks 

 and their tuffs. But for a few exceptions, belonging to the middle 

 zone, most of these latter schists belong to the upper zone; they 

 are represented by rocks of groups three (plagioclase gneiss), 

 four (metamorphosed gabbroid rocks), and five (schists containing 

 silicates of magnesia) . 



The age of this formation of schists in Central Celebes and in 

 other parts of the archipelago has been interpreted as follows : 



1. Wichmann' considers the mica schists of Central Celebes as 

 Archean; Martin^ does the same regarding those of Ceram, whereas 

 Verbeek^ thinks that those of South Borneo constitute a series of 

 Azoic rocks ; Volz'' refers to the Archean only the gneiss of the land 

 of the Gajos (North Sumatra). 



2. Molengraaff^ believes that the crystalline schists of Central 

 Borneo are partly Archean, partly of more recent age. 



3. Verbeek^ groups the gneiss and mica schists which he found 

 in the Moluccas, with other rocks, such as the quartzites (of dark 

 color) and argillaceous schists, in the "old schists formation," in 

 which he presumes^the existence of Azoic (e.g., the gneiss of Sibel- 

 aboe) or Archean elements, but also elements of the Old Paleozoic. 

 His opinion upon this matter is shared by Volz'^ and Ahlburg,^ who 

 also connect other rocks, such as the peridotite of eastern and 

 southeastern Celebes, with the mica schists. Volz draws attention 

 to the complete conformability between the mica schists and the 

 old schists in the aforementioned land of the Gajos. It must be 



^ "Der Posso-See in Celebes," in Petermann's Geogr. Mitte-iliingeii, Heft VII, 1896. 



^ "Reisen in den Molukken," Geologischer Theil, 1903. 



3 Jaarboek van het Mijnwezen, Vol. I, 1875. 



'' Nord-Sumatra, Vol. II, 191 2. 



s Geologische verkenningstockten in Centraat. Borneo, 1900. 



^ Rapport siir les Moluqties, 1908. ^ Nord-Sumatra, Vol. 1, 1909. 



* Versitch ciner geologischen DarsteUimg der Insel Celebes, 1913. 



