BY H. C. RICHARDS. 



185 



This estimated average composition for the whole of 

 the volcanic rocks of the area is based on rough general 

 calculations, but it may be regarded as approximately 

 correct. 



Calculated as Water-Free. 



I. — Average composition of Volcanic Rocks of Upper Division. 



II. — Average composition of Volcanic Recks of Middle Division. 

 III.— Average composition of Volcanic Rocks of Lower Division. 

 IV. — Average composition of Volcanic Rocks of all three Divisions. 



V. — Average composition of 87 Andesites. (a) 



VI. — Composition of Andesite from Tamhorine riatcau, por. 18, 

 parish Withe rin. 



(a) Daly. Igneou:; Rocks. 



