On the Occurrence of Lower Cambrian 

 Fossils in the Mount Lofty Ranges. 



By Walter Howchin, RG.S. 



[Read August 3, 1897.] 



For the past fifty years the stratigraphical position of the 

 Mount Lofty Eanges has been one of the most difficult, yet in- 

 teresting, problems in South Australian geology. A great ram- 

 part of rock, nearly 500 miles in its longer axis, its western 

 members composed of thick argillites, quartzites, siliceous lime- 

 stones and marbles ; and its easterly flanks passing into crystal- 

 line schists and great igneous intrusions, presents a bold 

 physiographical, as well as geological, contrast to the horizontal 

 beds which have gathered around its base. These serried heights 

 form the most conspicuous and extensive feature in our local 

 geology, and yet they have persistently held the secret of their 

 age. With two doubtful exceptions (quoted by the late Tenison 

 Woods) the most diligent search had failed to secure the faintest 

 palaeontological remains ; they were consequently regarded as 

 azoic and early observers classified them variously as older 

 Palaeozoic, or otherwise, Pre-Cambrian or Archaean. 



The discovery in 1879 of a sub-crystalline limestone containing 

 fossils of Lower Cambrian age, resting unconformably on a Pre- 

 Cambrian series on Yorke's Peninsula, was regarded as important 

 analogical evidence that the Mount Lofty formations were of 

 Pre-Cambrian age, and from the date of the discovery mentioned 

 the Mount Lofty Ranges have been generally classified as 

 Archaean. Discoveries have been recently made, however, in 

 these so-called Archaean rocks which have an important bearing 

 on this subject, and on the most convincing evidence determines 

 the basal beds of the Mount Lofty Ranges to be in part, if not 

 wholly, of Lower Cambrian age. The locality where the Cambrian 

 fossils were first observed was 



NORMANVILLE. 



It is to Professor T. W. Edgeworth David, of Sydney, that the 

 credit of a quickened interest in these old rocks is due. During 

 the past nine months he has sectioned for microscopical examina- 

 tion a great number of fragments of siliceous limestones and 

 cherty nodules belonging to this series, and in a sample of black 

 marble from Normanville he detected the remains of small 

 organisms, which he supposed to be pteropods. In March last 

 when Prof. David, Mr. C. C. Brittlebank of Victoria, and the 



