580 CASTS OF RADIOLAHIA IN PKE-CAMBKIAX ROCKS, 



Mr. H. Y. L. Brown, Government G-eologist of South Australia, 

 holds, however, a somewhat different view from the abo^e. Mr. 

 Brown considers that the low degree of metamorphism present in 

 the rocks of the western flanks of the Mt. Lofty range indicates 

 an age not eai'lier than the Cambrian, and that the Flinders and 

 Mt. Lofty beds really form one series. In his ofhcial G-eological 

 Map of South Australia, published in 1886, Mr. Brown recognises 

 three older formations in the ranges,' as follows : — 



(1). Paleozoic (Lower Silurian). — Comprising the less 



altered shales, sandstones, and limestones of the western 



portions. 

 (2). Palaeozoic, or Azoic — The micaceous, talcose, and 



hornblendic schists, quartzites and crystalline limestones 



^ a middle series towards the eastern side of the ranges. 

 (3). Arch.ean. — Metamorphic granite, gneiss, syenite, hoi'n- 



blendic and mica schists, crystalline limestones, 



quartzites, Arc, with igneous intrusions, rising beneath 



group No. 2 on the eastern flanks. 

 It will 1)6 observed from this table that the succession is inter- 

 pi'eted by INIr. Brown in an opposite way from that in which it is 

 explained by Prof. Tate, for whilst the latter considers the highly 

 metamorphic group the highest in the series, Mr. Brown places 

 this group at the base. 



On the whole it appears to us that Professor Tate's interpre- 

 tation is probabl)' the correct one, and if so the Bi-ighton rocks 

 must be low down in the Pre-Cambrian group. 



(b). Crystal Brook. — The rocks containing the casts of radio- 

 laria, at this locality, are thin laminated limestones, sandy 

 calcareous layers alternating with thin bands richer in lime. 

 Quartzite and banded argillites overlie the laminated limestones. 

 Lenticular beds of black chert or chalcedony occur on at least 15 

 liorizons in the limestone series. T]ie3Mxppear to be of later origin 

 than the enclosing rocks, like tlie flints in the Chalk Fttrmation of 

 Europe. The portion of the limestone series measured b}- us is at 

 least 1000 feet in thickness. The series is highly folded, and 



