﻿238 EEV. W. HOWCHIN ON GLACIAL EEDS OF [May I 908, 



The second fossiliferous horizon of the series occurs, from a 

 rough estimate, at about 1000 feet above the Arcliceocyathina- 

 Beds, in a pink or grey oolitic limestone in the Wirrialpa district. 

 The fossils are mainly confined to a band a few inches thick ; 

 but, within these limits, the rock is in places almost entirely 

 •composed of the massed and broken shells of Oholella and other 

 organisms, chiefly the former. Mr. Eobert Etheridge, jun., of the 

 Australian Museum, Sydney, has made the following determina- 

 tions from this bed ^ : — 



Olenellus sp. Orthis (1) Tatei, Etb. fil. 



Oholella wh'naljjcnsis, Eth. fil. Orthis (or Orthimia) sp. 



Oholella. wm-icdpensis, var. calceoloides, Hyolithes communis, Billings. 

 Etb. fil. 



That these limestones, with their typical Cambrian fossils, are 

 superior in position to the glacial beds can be verified by numerous 

 cross-sections. Xear Adelaide an uninterrupted succession of 

 outcrops (with a consistent westward dip), may he passed over in 

 a distance of 3 miles, showing an ascending series from the glacial 

 beds of the Sturt Valley to the purple slates and limestones of the 

 -coast near Brighton. 



The purple slates increase in breadth as they pass southwards 

 from this locality, and their continuity is broken by the fault- 

 escarpment of the Willunga range of hills. These hills, on their 

 coastal side, also consist of the purple-slate series ; but the fault 

 has brought the higher beds, including the Arcliceocyathvia-lAmQ- 

 stones, into close relationship with the lower slates and limestones. 

 Similar instances, where the superior position of the purple slates 

 to the glacial beds can be seen, occur between Mount Eemarkable 

 and the coast, and also in sections across the north-eastern portions 

 of the Flinders Ranges. 



Further evidence bearing on the geological age of the glacial 

 deposits is obtained by an examination of the beds which occur 

 below the glacial horizon (see fig. 1, p. 236). In this lower section 

 of the series the lithological features are in strong contrast vvdth 

 those exhibited by the upper beds. There is an entire absence of 

 the purple slates and fossiliferous limestones, the beds consisting 

 chiefly of thick felspathic quartzites, clay-slates, and phyllites, which 

 can be followed in a descending order of succession to the basal 

 grits and conglomerates resting on a pre-Cambrian complex.^ 



The beds of glacial origin are separated from the base of the 

 Cambrian series, by a less thickness of rock than that which inter- 

 venes between them and the limestones containing the Cambrian 

 fauna near the upper limits of the Cambrian series. 



1 Trans. Eoy. Soc. S. Austral, vol. xxix (1905) p. 246. 



2 For particulars of the lower members of the Cambrian series, see ' The 

 Geology of the Mount-Lofty Eanges, Part II' Trans. Eoy. Soc. S. Austral 

 vol. XXX (1906) p. 227. 



