554 HADIOLAIUA IN PALAEOZOIC KOCKS, 



of the granules is only very faintly marked. The orders of 

 Prunoidea, Discoidea and Cyrtoidea are all represented. The 

 geological horizon to which they belong is very probably that of 

 the Desert Sandstone Formation (Upper Cretaceous). 



What is probably an equi\alent of this rock has been described 

 1)}^ the Rev. J. E. Tenison Woods* as follows : — 



"What we find whenever a good section is exposed is this — a 

 layer of loose white, or red, decomposed rock or rubble, some 3 or 

 4 feet thick, lies on the upturned edges of the slates. Above 

 this a layer some 2 feet thick of loamy earth, which has been 

 surface soil. Above this from 14 to 120 feet of magnesite or 

 carbonate of magnesia, more or less impure, with silicates of 

 alumina and iron, and mere traces of lime. Not often is it pure 

 white, for the stains of brown, red and purple, from iron oxide, 

 permeate the whole." 



The above statement l)y the Rev. J. E. Tenison- Woods, as 

 far as can be ascertained, refers to a rock identical with that 

 which has now l)een proved to be, not a magnesite, but a radio- 

 larian rock. 



Reference may here be made to a note by Dr. Hindef in which 

 he describes a cherty rock from South Australia, which although 

 -derived from sponge spicules rather than radiolaria, yet contains 

 globules of opal silica which might easily be mistaken for 

 radiolaria. 



The rock described in the note referred to above appears to be 

 of Tertiary age. The specimens were collected by Mr. H. Y. L. 

 Brown at Yorke's Peninsula, near Adelaide. Dr. Hinde states 

 {o20. cit. p. 115), "The principal feature is the occurrence of 

 detached sponge-spicules which in places are heterogeneously 

 crowded tosether in the rock. . . . The matrix in which the 



* Report on Geology and Mineralogy of the Nortliern Territory, South 

 Australia, p. 5. By authority. Adelaide, 1886. 



+ "Note on Specimens of Cherty Siliceous Rock from South Australia." 

 Oeol. Mag. New Series. Dec. iii. Vol. viii. 1891. pp. 115-116. 



