BY T. W. EDCiEWORTfl DAVID, 000 



spicules and quartz grains are iml)eflded appears to be mainly of 

 amorphous or opal silica, nearly entirely neutral to polarized 

 light between crossed Nicols, and it is principally in the form of 

 very minute globules or discs usually aggregated together so as 

 to exhibit a microscopic botryoidal appearance, the globules or 

 discs varying from 01 to 'OS mm. in diameter. The globular 

 form of opal silica is similar to that which occurs in many of the 

 sponge-beds of the Upper Greensand in this country, and there 

 can hardly be any doubt that in this Australian Chert it is due, 

 as in the Chert of this country, to the solution and redeposition 

 of the organic silica of the sponge-spicules." 



As far as I am aware, the above are the only references to 

 the occurrence of I'adiolarian rocks in Australia; and in both 

 cases it would appear that the rocks mentioned are of late 

 Mesozoic age. 



Before proceeding to describe the horizons where radiolaria 

 have recently been observed by me in Palasozoic rocks in IST.S.W., 

 it might be of interest, in view of the grand scale on which the 

 radio! arian rocks are now known to be developed in this colony, 

 and in view also of the fact that some of the literature relating 

 to radiolaria is rather inaccessible to Australian geologists, to 

 briefly summarize the more important works relating to Palaeozoic 

 and Mesozoic radiolaria in Extra- Australian areas. 



Radiolaria have been descriljed l:)y Dr. D. Riist* from Mesozoic 

 rocks, the Gault of Zilli, and the Neocomiaii:- of Gardenazza. 

 The radiolai'ia in the best state of preservation were those found 

 in the Cretaceous Coprolite Beds of Zilli, in 8axony. These 

 radiolaria have been admirably figured and described by this 

 observer. 



Dunikowski has described perfect forms from the Lower Lias 

 of the Austrian Alps; while Hantken believes that certain 

 siliceous limestones with Aptycus, of Upper Jurassic age, in 

 Central Europe are almost entirely formed of radiolaria. 



* Palpeontogi'aphica. Vol. xxxi. 1885, and ibidem Vol. xxxiv. pp. 181- 

 213. Pis. xxli-xxix., 18SS, and Vol. xxxviii,, 1892. 



