22 PLANT-BEARING COMMON BLACK OPAL. 



dissolved silica from rocks through which the water passed 

 and that this silica and some of the water wa« depositee 

 in depressions in the form of common black opal. 



j:xi'laxatiox ur plates. 



Plate I. 



Fiji. 1- — Photoraiciojrraph of section of (Jommou Black Opal. Tweed 

 Heatls, New South Wales, showins fiagmenLs of plants, and an elliptical 

 section possibly radiolarian, in a ground mass of opal. > 14 diameters, 

 ordinary light. 



Fig. 2. — Photomicrograph of .section of Common Black Opal, Tweed 

 Heads. New South Wales. Section showing plant remains in matrix of 

 light brown coloured opal, y 120 diameter.s. ordinary light. 



Plate II. 



Fig. 1. — Photomicrograph of section of Common Black Opal, Tweed 

 Heads, New South Wales. The cell structure of a plant adjoins a crack in 

 centre of section. X 120 diameters, ordinary light. 



Fig. 2. — Photomicrograph of section of Common Black Opal, Tweed 

 Heads, New South Wales. In the centre of the field is an oblique .section' 

 of leg of an arthropod which may be a spider. Surrounding it are plant 

 fragments and concretions of pyrite, in a matrix of brown opal. 

 X 120 diameters, ordinary light. 



