571 



NOTE ON THE OCCURRENCE OF CASTS OF RAD 10- 

 LARIA IN PRE-CAMBRIAN (0 ROCKS, SOUTPI 

 AUSTRALIA. 



By Pkofessor T. W. Edgeworth David, B.A., F.G.S., 

 AND Walter Howchin, F.G-.S. 



(Plates xxxix-.xL.) 



CONTENTS. 



1. Iiitioduction. 



2. Bibliography. 



3. Description of the Radiolaria. 



4. Geological Horizon of the Radiolarian Rock. 



5. Smninaiy and Deductions. 



1. Introduction. 



Through the kindness of Professor R. Tate, of Adelaide Uni- 

 versity, one of us was enabled last December year to make a cursory 

 examination of some of the Pi-e-Cambi-ian i-ocks in the neighbour- 

 hood of Hallett's Cove, about fifteen miles S.S.W. from Adelaide. 



Thin sections of some of these rocks, subsequently prepared at 

 Sydney University, showed not only well marked oolitic structure, 

 in the case of some of the calcareous rocks, but also obscure 

 traces of what are probably radiolaria. The latter were visible 

 chiefly in a dark greenish-grey siliceovis limestone, as well as in a 

 very fine grained laminated dark grey clay-shale. 



A correspondence followed between us on the subject and, as it 

 became apparent that both of us had been working for some time 

 previous on the subject of micro-organisms in the Pre-Cambrian 

 rocks of Australia, we decided to collaborate, and accordingly 

 have written this preliminary note. 



