506 



Transactions. — Geology. 



Analysis o 



/ the Slate. 





Moisture driven off at 105° C. 



> 



•475 



* Water lost at a rel heat 







. 3-143 



Silica 







. 52-259 



Alumina .. 







. 20-724 



Iron sesquioxide 







. 2-207 



„ protoxide . . 







. 5-094 



Phosphoric acid . . 







. absent 



Manganese protoxide . . 







. 1-727 



Lime .. 







. 2-984 



Magnesia 







. 4-199 



Potash 







. 4-353 



Soda .. 







. 3-072 



Carbonic acid . . 







traces 



100-237 



Specific gravity = 2-713. 



It will be at once observed that there is far less silica in the slaty portion 

 than in the granitic, and that the bases have undergone a corresponding 

 increase in their amounts ; this is most noticeable in the percentage of iron, 

 alumina, manganese, and magnesia. The increase in the proportions of the 

 bases present has been accompanied by a rise in the specific gravity of the 

 slaty portion. 



Note. — This specimen was obtained by myself in Isthmus Sound, Preservation 

 Inlet. See " Geology of Otago," Dunedin, 1875, p. 40.— F. W. H. 



This was estimated by direct weighing in a calcium chloride drying-tube. 



