BY H. C. RICHARDS. 201 



up by Harker.^^ In this way a comparison is obtained, not 

 only of the rocks under consideration, but also of these 

 with the world's average alkaline and sub-alkaline series. 



Plate VI. shows diagrams for lime and magnesia. 



Plate VII. shows diagrams for soda, potash and also 

 combined soda and potash, 



Plate VIII. shows diagrams for alumina and total iron- 

 oxides as ferrous oxide. 



Plate IX. shows a diagram for combined alumina and 

 total iron-oxides as ferrous oxide. 



The numbers of the rocks correspond to those given 

 on Table A^I. (page 183). 



Plate X. 



Geological Sketch-Map. 



This is drawn up on a scale of six miles to an inch 

 and is based on maps published by the Geological Survey 

 and by H. I. Jensen, D.Sc, with additions and alterations 

 by the author. It shows the extent and distribution of the 

 volcanic rocks of the area. No attempt has been made to 

 map in the other igneous rocks which intrude the Paleo- 

 zoic rocks in the northern part of the area. 



The basaltic and andesitic rocks of both the upper and 

 lower divisions have been denoted by the same marking. 



The thick l)lack lines across the map indicate the lines 

 of the sections shown on Plate XI. 



Plate XI. 

 Geological Sketch-Sections. 



This contains four geological sketch-sections which 

 have been drawn along lines which are marked on the 

 map (Plate X.) by continuous thick black lines. 



Fig. I. — Geological sketch-section in a north-easterly 

 direction from the Main Range to Mount 

 Flinders, and then east to the Pacific Ocean. 



"^ Harker, jSTat. Hist. Igneou^ Rocks, pp. 150, 151 

 G 



