BY H. C. RICHARDS. 



193 



resulted. This series is, perhaps, more closely allied to the 

 sub-alkaline series than to the alkaline series. An estimate 

 of the average composition of this series has been made, 

 and in doing so the nine rocks analysed were taken as 

 equally proportionate. Analyses used were those of rocks 

 numbered 5, 8, 11, 17, 19, 22, 27, 28, 35. 



Table IX. — Average Compositions. 



II. 



III. 



SiO, 



AI063 



Fe,03 



FeO 



MgO 



CaO 



NagO 



KjO 



H,0 + 



h:o- 



TiOa 

 P2O5 

 MnO 



Total 



Calculated as Water -Free. 



I. — Average Composition of Alkaline Series of Volcanic Rocks. 



II. — Average Composition of Sub-alkaline Series of Volcanic 

 Rocks. 



III. — Average Composition of Series intermediate between Alka- 

 line aiid Sub-alkaline. 



