564 E. C. ABENDANON 



remarked that a similar conformability has been discovered 

 nowhere else in the archipelago by any of the other explorers. 



4. The rare true mica schists of Letti are regarded by Molen- 

 graaff^ as metamorphosed rocks of the Old Permian. 



5. By Wing Easton,^ but more expressly by Volz and Tobler,^ 

 the "old" schists are considered as being partially Mesozoic. One 

 may doubt, however, whether they include real mica schists. 



6. Smith'' expresses much doubt about the Archean age ascribed 

 to the crystalline schists of the Philippine Islands, and he assigns 

 many of them to the Tertiary. 



There is thus a strong discrepancy in the opinions of these 

 competent explorers, as the ages they assign to the schists vary 

 from the Archean to the Tertiary. Their opinions could hardly 

 differ more. 



In order to come to a personal conclusion, I shall begin by 

 trying to solve a few questions. First of all: Do all the series of 

 rocks which the above-mentioned explorers have classed with the 

 "old schists formation," really belong to it? 



It would perhaps be possible to answer this question with 

 certainty if one had gathered into a single collection all the rocks 

 collected; but such a collection does not exist. On the contrary, 

 those assembled by the explorers named are scattered in such a 

 large number of museums that a comparative petrographic exam- 

 ination of the crystalline schists and old schists existing in the 

 different parts of the Dutch East Indian Archipelago is absolutely 

 impossible. One thing is certain, however, and that is that the 

 rocks included in the "old schists formation" have been put 

 together on a basis of negative characters, namely, their "old" 

 appearance and the absence of fossils. It is therefore possible, 

 perhaps very probable, that elements have been included which in 

 fact do not belong to the old schists formation. 



In order to come to a more accurate classification, it appears 

 necessary to make, first of all, a distinction between the gneiss and 

 crystalline schists on the one side, and the "old" schists on the other 



^ Jaarb. Mijnwezen, 1914. ^ Ibid., 1904. j 



3 Voorl. med. over de geologic der res. Djambi, 191 2. 



'^ Handbuch der regionalem Geologic, Philippine Islands, 1910. 



