Metamorphic and Plutonic Rocks at Orneo. 107 



The mineralogical characters of these schists will be 

 understood better from the following examples. The letters 

 prefixed to the descriptions refer to those appended to the 

 diagram Fig. 2, Plate I. 



(a) Nodular mica schist striking N. 30°-40° W. The beds 

 at this place are not all of them nodular, and they vary also 

 in colour and in the relative amounts of quartz and mica. 

 This sample I examined in a thin slice. I found the main 

 mass of the rock to be a mixture of brown magiiesia mica, 

 and of colourless muscovite in small overlapping plates. 

 In this are very numerous short, stout, light-coloured crystals 

 of tourmaline from 004^ x -002 inches down to '0015 x •001 

 inches in dimensions. There is a considerable amount of 

 black iron ore scattered throughout the slice. No quartz 

 is visible in the several slices examined. I have to thank 

 Mr. Jas. C. Fraser for the subjoined analysis of this rock : — 



Analysis 



No. 3.- 



-MicA Schist. 



SlO^ 







58-87 



AI.2O3 









16-95 



Fe.203 . 









8-62 



Fe.O 









3-93 



Ca.O 









•97 



Mg.O 









2-32 



K,0 









5-98 



Na^O 









1-48 



Li^O 









tr.* 



B2O3 









tr. 





99-12 



A second sample from the same place (a Fig. 2, Plate I) 

 is of one of the quartzose beds. In the hand sample it is a 

 somewhat fissile schist of a greyish to yellowish colour, and 

 the foliations very glistening with plates of muscovite. 

 Under the lens can be seen plates of rather pearly mica, very 

 little brown magnesia mica, and numerous crj^'stals of tour- 

 maline can be made out. Under the microscope a thin 

 slice of this rock shows a far gTeater amount of quartz than 

 there is in those beds of which the last described is a sample. 

 With the quartz grains there is a colourless mica, and there 

 are numerous tourmaline crystals of somewhat larger size than 

 those in the last-mentioned rock. These crystals lie mostly 



* Determined by spectroscope only. 



