BY T. W. EDGEWORTH DAVID AND WALTER IIOWCHIX. 579 



Mr. R. Etheridge, Junr., to be of Cambrian age),* resting un- 

 conformabl}' on an older series of mica slates and talcose schists, 

 supplied new data bearing on the possible age of the Mt. Lofty 

 formation. The basal or Pre-Cambrian beds at Ardrossan, exhibit 

 a close lithological resemblance to many portions of the Mt. 

 Lofty series, and may provisionally be considered to be homotaxial 

 with the latter. Unfortunately, in no other place in South Aus- 

 tralia, that we know of, are the Cambrian and Pre Cambrian 

 rocks seen in juxtaposition, but they have been observed in the 

 Flinders Ranges in close proximity to the Pre-Cambrian rocks, 

 and it has been noticed that the two groups exhibit strongly 

 marked lithological differences as well as probable unconformity 



(PI. XL. fig. 2). 



Prof. R Tate has for many years advocated the Pre-Cambrian 

 (or Archi^an) age of the Mt. Lofty formation.! The chief con- 

 siderations for this view are based on — 



(a) The evidence afforded by the unconformity between tlie 

 Lower Cambrian and the Pre-Cambrian rocks near Ardrossan, 

 and the general resemblance of the inferior rocks of that section to 

 the Mt. Lofty beds (PL xl. fig. 1), (and so to the Brighton rocks). 



(b) In the Flinders Range two formations have l:)een noted 

 (although not seen in contact) in which the less altered beds with 

 lower angle of dip have been determined by their included fossils 

 {Archceoci/athiiice, Olene'lus, iialterella, etc.) to be Cambrian; and 

 it has been inferred that the more highly metamorphic rocks with 

 higher angle of dip are unconformable and consequently Pre- 

 Cambrian. The Mt. Lofty beds are continuous with those of the 

 Flinders Range. 



(c) The absence of fossils (macroscopic) throughout the whole 

 of the Mt. Lofty series, even in places where limestones and 

 shales occur so little metamorphosed that we have no reason to 

 think that oi'ganic remains, if originally present, have been 

 obliterated by molecular rearrangement. 



»Roy. Soc. S. Aust. 1890, p. 10, and R. Tate ibidem 1892, pp. 183-1S9. 

 tEoy. Sue. S. Aust. \o\. xiii. 1890, p. 20: Aust. Assoc. .'Ad. Sc. 0/a cit. ante. 



